Naively as an outsider, this situation seems like everything worked as intended?
On a nominally 2h45m flight, they spent an extra 2 hours in the air, presumably doing doing fuel intensive altitude changing maneuvers, and were eventually able to land safely with their reserves almost exhausted.
I’m a little confused by what there is to investigate at all.
How much fuel should they have landed with?
In safety-critical systems, we distinguish between accidents (actual loss, e.g. lives, equipment, etc.) and hazardous states. The equation is
hazardous state + environmental conditions = accident
Since we can only control the system, and not its environment, we focus on preventing hazardous states, rather than accidents. If we can keep the system out of all hazardous states, we also avoid accidents. (Trying to prevent accidents while not paying attention to hazardous states amounts to relying on the environment always being on our side, and is bound to fail eventually.)
One such hazardous state we have defined in aviation is "less than N minutes of fuel remaining when landing". If an aircraft lands with less than N minutes of fuel on board, it would only have taken bad environmental conditions to make it crash, rather than land. Thus we design commercial aviation so that planes always have N minutes of fuel remaining when landing. If they don't, that's a big deal: they've entered a hazardous state, and we never want to see that. (I don't remember if N is 30 or 45 or 60 but somewhere in that region.)
For another example, one of my children loves playing around cliffs and rocks. Initially he was very keen on promising me that he wouldn't fall down. I explained the difference between accidents and hazardous states to him in childrens' terms, and he realised slowly that he cannot control whether or not he has an accident, so it's a bad idea to promise me that he won't have an accident. What he can control is whether or not bad environmental conditions lead to an accident, and he does that by keeping out of hazardous states. In this case, the hazardous state would be standing less than a child-height within a ledge when there is nobody below ready to catch. He can promise me to avoid that, and that satisfies me a lot more than a promise to not fall.
If you haven't done so: please write a book. Aim it towards software professionals in non-regulated industries. I promise to buy 50 to give to all of my software developing colleagues.
As for 'N', for turboprops it is 45, for jets it is 30.
I want to write more about this, but it has been a really difficult subject to structure. I gave up halfway through this article, for example, and never published it – I didn't even get around to editing it, so it's mostly bad stream of consciousness stuff: https://entropicthoughts.com/root-cause-analysis-youre-doing...
I intend to come back to it some day, but I do not think that day is today.
Just started reading the linked text after reading your comment and I agree, this is high quality education, and enjoyable. It's an art, really. Thank you for sharing your work and please keep it up.
Just a thought I had while reading your introduction: this is applicable even to running a successful business model. I'm honestly having trouble even putting it into words, but you have my analytical mind going now at a very late hour... Thanks!
Ok. I am impressed with your ability to take such complex subjects and make them plain, you are delivering very high quality here. The subject is absolutely underserved in the industry as far as I'm aware of it, and I would love to have a book that I can hand out to people working on software in critical infrastructure and life sciences that gets them up to speed. The annoying thing is that software skills are values much higher than the ability to accurate model the risks because that is only seen as a function of small choices standing by themselves. A larger, overall approach is what is very often called for and it would help to have a tool in hand to both make that case and to give the counterparty the vocabulary and the required understanding of the subject in order to have a meaningful conversation.
Edit: please post your link from above as a separate submission.
Write it as a children's book. A literal ELI5.
(Knowing, of course, that it will still be read mainly by engineers. But that's the charm.)
I have a rather over-confident five year old, so would LOVE that book right now.
Your writing is good, please keep at it. I think it would help a lot if you made it clearer when you're talking between root-cause-analysis for software, aviation, other things, or generically.
Also, your train-of-thought is pretty deep; bulleting runs out of steam and gets visually confusing, especially with the article table-of-contents on RHS, you're only using <50% of screen width. Suggest you need numbered/lettered lists and section headings and use the full screen width.
Thanks, I would buy your book. But I understand the effort necessary all too well.
If he aims it toward five year olds as he had explained it, bet it would be even more applicable to our profession.
Having spent some time with my five year old nieces and nephews, sometimes I wonder if five year olds could run companies better.
(note: obviously sarcastic but kids really do have some amazing insights that we forget when trying to chase KPIs or revenue)
See also: various points in the Evil Overlord list[0]. Selected examples:
[0] https://tvtropes.org/pmwiki/pmwiki.php/Main/EvilOverlordListI'd never seen that list before but it's hilarious!
Seconded.
That being said: I have - for some years now - started to read air accident board reports (depending on your locale, they may be named slightly different). They make for a fascinating read, and they have made me approach debugging and postmortems in a more structured, more holistic way. They should be freely available on your transportation safety board websites (NTSB in America, BFU in Germany, ...)
Google’s SRE STPA starts with a similar model. I haven’t read the external document, but my team went through this process internally and we considered the hazardous states and environmental triggers.
https://sre.google/stpa/teaching
Disclaimer: currently employed by Google, this message is not sponsored.
Seconded! This was an extremely well written and well thought out explanation of this idea. Would love to read more along these lines.
(Will now be checking out your blog.)
Also check out risks digest:
https://catless.ncl.ac.uk/Risks/
[dead]
> Trying to prevent accidents while not paying attention to hazardous states amounts to relying on the environment always being on our side, and is bound to fail eventually.
The reason they had less than 30 minutes of fuel was because the environment wasn't on their side. They started out with a normal amount of reserve and then things went quite badly and the reserve was sufficient but only just.
The question then is, how much of an outlier was this? Was this a perfect storm that only happens once in a century and the thing worse than this that would actually have exhausted the reserve only happens once in ten centuries? Or are planes doing this every Tuesday which would imply that something is very wrong?
This is why staying out of hazardous conditions is a dynamic control problem, rather than a simple equation or plan you can set up ahead of time.
There are multiple controllers interacting with the system (the FADEC computer in the engines, the flight management computer in the plane, pilots, ground crew, dispatchers, air traffic controllers, the people at EASA drafting regulations, etc.), trying to keep it outside of hazardous conditions. They do so by observing the state the system and the environment is in ("feedback"), running simulations of how it will evolve in the future ("mental models"), and making adjustments to the system ("control inputs") to keep it outside of hazardous conditions.
Whenever the system enters a hazardous condition, there was something that made these controllers insufficient. Either someone had inadequate feedback, or inadequate mental models, or the control inputs were inoperational or insufficient. Or sometimes an entire controller that ought to have been there was missing!
In this case it seems like the hazard could have been avoided any number of ways: ground the plane, add more fuel, divert sooner, be more conservative about weather on alternates, etc. Which control input is appropriate and how to ensure it is enacted in the future is up to the real investigators with access to all data necessary.
-----
You are correct that we will not ever be able to set up a system where all controllers are able to always keep it out of hazardous states perfectly. If that was a thing we would never have any accident ever – we would only have intentional losses that are calculated to be worth their revenue in additional efficiency.
But by adopting the right framework for thinking about this ("how do active controllers dynamically keep the system out of hazards?") we can do a pretty good job of preventing most such problems. The good news is that predicting hazardous states is much easier than predicting accidents, so we can actually do a lot of this design up-front without first having an accident happen and then learning from it.
> This is why staying out of hazardous conditions is a dynamic control problem
I don't think this philosophy can work.
If you can't control whether the environment will push you from a hazardous state into a failure state, you also can't control whether the environment will push you from a nonhazardous state into a hazardous state.
If staying out of hazardous conditions is a dynamic control problem requiring on-the-fly adjustment from local actors, exactly the same thing is true of staying out of failure states.
The point of defining hazardous states is that they are a buffer between you and failure. Sometimes you actually need the buffer. If you didn't, the hazardous state wouldn't be hazardous.
But the only possible outcome of treating entering a hazardous state as equivalent to entering a failure state is that you start panicking whenever an airplane touches down with less than a hundred thousand gallons of fuel.
My understanding is that the SOP for low fuel is that you need to declare a fuel emergency (i.e., "Mayday Mayday Mayday Fuel") one you reach the point where you will land with only reserve fuel left. The point OP was making is that the entire system of fuel planning is designed so that you should never reach the Mayday stage as a result of something you can expect to happen eventually (such as really bad weather). If you land with reserve fuel, it is normally investigated like any other emergency.
Flight plans require you to look at the weather reports of your destination before you take off and pick at least one or two alternates that will let you divert if the weather is marginal. The fuel you load includes several redundancies to deal with different unexpected conditions[1] as well as the need to divert if you cannot land.
There have been a few historical cases of planes running out of fuel (and quite a few cases of planes landing with only reserve fuel), and usually the root cause was a pilot not making the decision to go to an alternate airport soon enough or not declaring an emergency immediately -- even with very dynamic weather conditions you should have enough fuel for a go-around, holding, and going to an alternate.
[1]: https://www.casa.gov.au/guidelines-aircraft-fuel-requirement...
Landing at an alternate location is significantly more expensive, so I assume Ryanair put pressure on its pilots to avoid that…?
We'll find out in the investigation, but "get-there-itis" is a very common condition amongst pilots and can lead to them delaying making decisions (such as going to alternates) so it's possible that this happened without explicit (or implicit) pressure from management.
That being said, the fact that (AFAICS) they first tried to divert to a closer airport where the weather was similar rather than an alternate with clear weather was probably one of the causes of this event.
That's very enlightening. I'm casually interested in traffic safety and road/junction designs from the perspective of a UK cyclist and there's a lot to be learnt from the safety culture/practices of the aviation industry. I typically think in terms of "safety margins" whilst cycling (e.g. if a driver pulls out of a side road in front of me, how quickly can I avoid them via swerving or brake to avoid a collision). I can imagine that hazardous states can be applied to a lot of the traffic behaviour at junctions.
Well said, will think about asking this attitude towards my child, seems very helpful
As others have said, final fuel reserves are typically at least half an hour, and you shouldn't really be cutting into them. What if their first approach into MAN had led to another go around?
With a major storm heading north-easterly across the UK, the planning should have reasonably foreseen that an airport 56 miles east may also be unavailable, and should've further diverted prior to that point.
They likely used the majority of their final fuel reserve on the secondary diversion from EDI to MAN, presumably having planned to land at their alternate (EDI) around the time they reached the final fuel reserve.
Any CAA report into this, if there is one produced, is going to be interesting, because there's multiple people having made multiple decisions that led to this.
Suspect they were IFR. All your points stand. First time flying things with a jet engine, I was shocked how much more fuel gets burned at low altitude. It almost always works out better to max climb to altitude and descend than to fly low and level. On a small jet, things can get spicy fast when ATC route you around at 5000' for 15 minutes or so. Three aborted landings would gobble gas like crazy.
§ 91.167 Fuel requirements for flight in IFR conditions.
(a) No person may operate a civil aircraft in IFR conditions unless it carries enough fuel (considering weather reports and forecasts and weather conditions) to—
(1) Complete the flight to the first airport of intended landing;
(2) Except as provided in paragraph (b) of this section, fly from that airport to the alternate airport; and
(3) Fly after that for 45 minutes at normal cruising speed
They were most definitely IFR. Not because of the weather but because IFR is required above certain altitude 18,000 ft in the U.S. and typically lower in Europe (depends on a country). Jets including small private jets are almost always on IFR. Airliners with passengers - always.
Why does it burn fuel so fast?
My guess is higher air density means more wind resistance, which acts as negative forward acceleration.
Not just that. Jet engines are efficient at higher speeds because the exhaust of the jet engine is fast.
If the plane is going fast as well, that exhaust is more or less stationary relative to the ground. The engine works to exchange the position of the plane with the position of the air in front of it.
If the plane is going slow, it's accelerating the air backwards. That's where the work is going, making the engine less efficient.
Think about it this way: if the jet airplane is tied to the ground, its engines are running at 0% efficiency, working hard to blow the air backwards. You wouldn't want to stand behind a jet engine when the plane is about to take off, when that's effectively the case.
The same applies to propeller-driven planes, of course. But those can vary the prop speed as well as propeller pitch, having more control on how fast the air is being pushed backwards. This allows the engine to be efficient at a wider ranger of speeds, particularly, at the slower range.
But the propeller has a limit of how fast it can push the air back. When the prop blades start reaching the speed of sound, weird shit starts happening [1]. So propeller-driven aircraft have a limit on speeds at which they can go efficiently.
Jet engines (turbofans when it comes to airliners) trade off low efficiency at low speed / low altitude (where the airplane is spending a small percentage of flight time) for higher efficiency at high speed / high altitude.
Variable pitch turbine fans[2] aim to address this tradeoff, but the tech has yet to catch on.
[1] https://en.wikipedia.org/wiki/Republic_XF-84H_Thunderscreech
[2] https://en.wikipedia.org/wiki/Variable_pitch_fan
That sounds like Oberth effect in rocketry, where the faster you go the more efficient your rocket be: https://en.wikipedia.org/wiki/Oberth_effect
they have nothing to do with each other.
I think about it like this:
Jet needs to suck air from front. If air is stopped, sucking is hard. If air is already being thrown at you, you don't even need to suck, just let it come in.
You are right that accelerating the air backwards more reduces efficiency but I think it should be mentioned that the jet engine has to accelerate the air backwards to do any work pushing the plane forward. Picking it up and setting it back down affects the air with a net force of zero and therefore the force pushing the plane forward is also zero.
So perhaps the differential air speed between the intake and exhaust is a big factor in the efficiency equation? The bigger the difference the more work is needed..
Variable pitch turbine fans sound very interesting! Perhaps in the future as tech improves and fuel efficiency incentives continue to increase.
So, newton's first law?
Just reaching altitude again to make it to the first and later second alternate are mostly likely the biggest factors in the extra fuel consumption. That's very expensive.
The 30 min reserve is on top of the fuel needed to reach the alternate and do a landing there, so only the flight to the second alternate, plus the 2nd and 3rd landings at the initial destination would have cut into the reserve.
With 100mph winds I could easily see the 30 min reserve being eaten up by the flight from Edinburgh to Manchester. It's 178 miles! It takes a good 15-20 minutes to cross that distance when flying normally, add ascent & descent time and the landing pattern and you're easily at 24 minutes.
Edit: in other comments here, it seems like Edinburgh to Manchester is a 45 minute flight. So yeah, they could easily have been outside of reserves when they did the go-around at Edinburgh and still had only 6 minutes left at Manchester.
Yeah, although it depends what the alternate was in the flight plan. It may have been Manchester. Although I think its more likely it was Edinburgh, which in the circumstances was too optimistic. Too much concern about the minimal costs of fuel tankering to add a bit more gas? Or saving time by not refuelling?
Ive never flown on Ryanair and dont intend to.
As far as I’ve heard, Ryanair will cut into literally everything (including comfort and decency) for the sake of efficiency – other than safety. Even if they wanted to, they're subject to the same commercial aviation regulations as everybody else.
Do you have anything other than this single incident to back up your insinuation that they’re less safe than a full service airline?
I don't know how true this is but I have heard Ryanair will use the absolute legal minimum amount of fuel whenever possible whereas other airlines might fly with a bit more.
In theory though that shouldn't matter because as you say, the legal minimum should really be enough.
That seems like a cost/convenience tradeoff: The implication of only carrying minimum fuel is that the pilots can't hold for long to see if conditions improve and instead have to immediately go for the alternate destination airport.
The consequence of that is everybody ending up in the wrong place, but not in an unsafe way.
The flight plans I've seen accounted for two alternates, not one, a significant time in a holding pattern and up to three go-arounds. This was for cargo 747s and a while ago so chances are the regulations have changed by now, also, it may have been due to the kind of cargo.
From what I can tell, that only seems to apply to EASA since 2022. As it took off from an EU airport and landed in the UK, I don't know if that rule would apply.
You get that energy back on descent, no?
4 replies and 3 are dismissing even the idea..
Yes, you get "some" back, and its not negligible amount. Typical modern airliner can descend on 15-20:1, giving you over 150-200km (90-120mi) range from typical cruising altitude of 33 000 feet even with engines off. Most everyday descents are actually done by maintaining altitude as long as possible, and then iddling the engines fully for as long as clearance allows. (Ofc you then use engines as you geat nearer, because its safer to be a little low when stabilizing on approach, than a little high)
Thanks to turbofans(edited from turboprops) better efficiency + less drag at higher altitude its actually more fuel economical to command full thrust and gain altitude quickly, than slower climb, or maintaining altitude (which goes against our intuition from cars, where if you wanna get far, you never give full throttle).
But theres still some drag, so you dont get everything back, so you generally want to avoid murking in low altitudes as long as possible. Full thrust repeatedly at lowest altitudes (from failed go arounds) is the least economical part of flight, so you want to avoid those if possible. But its true that the altitude you gain is equivalent to "banking" the energy, just not all of it.
(1) this was a jet, not a turboprop
Edit: changed turbofan into turbprop, which is what I meant.
(2) fuel burned stays burned, you don't 'get it back'
(3) the altitude gained may have been adjusted to account for the low fuel situation
(4) the winds are a major factor here, far larger than the fact that 'what goes up must come down', something that is already taken into account when computing the fuel reserve in the first place.
So it seems. But because you want to land you then want to shed all that velocity. So you 'get it back' only to have to waste the bigger fraction of it. A go around is much like a mini take-off, you just miss the runway portion of it.
Nah. You want to land, but you are really not shedding most of your velocity until after touchdown. What you gain by burning fuel is energy, and you can either bank it into altitude, or velocity. You must shed both to land, but not so for go-around. There you shed almost all of your altitude, but you keep most of your velocity -> you still have a lot of energy left. That's why on go-around you spool your engines and start climbing basically right away, unlike typical takeoff, where after spooling up the engines you are still earth-bound until you build enough velocity.
So you only ever really lost your "altitude" component of energy, not "velocity" one. You run your engines at TOGA (Take Off / Go Around = maximum thrust), thrust to gain mainly altitude, only increasing speed a little bit. Then on another approach attempt you use both the altitude and excess velocity bank again.
In flight, ~all your energy losses go to drag. Doesn't matter if you bank it into speed or altitude, both is exchanged to be at minimums (0 altitude above ground, lowest safe landing speed) at touchdown. If you produce extra energy in your engines, it has to go to either speed or altitude, which you then pull out again, usually by maintaining speed while lowering altitude while having engines at idle.
(1) The turbofan category of jet engine seems to inspire a lot of very pretty animated technical diagrams—here’s one set from a German manufacturer [0]. Now if only we could convince Bartozs Ciechanowski to take on such a subject… [1]
(2) I know glider pilots who fly without any fuel at all, once aloft… sounds not unlike the 150-200km glide range that @MaxikCZ mentions at idle from cruising altitude.
[0] https://aeroreport.de/en/good-to-know/how-does-a-turbofan-en...
[1] e.g. https://ciechanow.ski/airfoil/
Aircraft that are designed as gliders are much lighter and thus have much longer glide range than aircraft that aren't. They're so lightweight that they can climb on thermals. A 737 is not going to be able to do that, but a regular glider can't fly at 400 knots.
> thus have much longer glide range
Im gonna be a little pedantic, but the weight has surprisingly small effect on glide range, actually none of the weight affect the range directly, its all from secondary effects.
The glide is given mainly by drag and lift (so body and wing geometry), correlated to certain speed. The weight isnt in the equation at all. What weight does, is increases the speed in which the aircraft achieves this maximum glide ratio, and in higher speed you have higher drag, which finally reduces the range.
Thats why many modern gliders have water tanks in wings, to increase the weight of the glider, moving planes speed of best glide ratio higher, allowing for more efficiency at higher speeds. Its worth it if the atmospheric condition provide strong lifts. Pilot can then dump the water in flight to reduce the wing load, allowing them to land with less speed, or just keep in the air longer as thermals get weaker in the afternoon/evening
(source, I used to be a glider pilot)
It should also be noted that gliders have crazy aspect ratios. Airliner wings are designed for completely different flight envelopes than gliders, it’s all a game of what you optimize for and what trade offs you are willing and/or required to make.
But of course that doesn’t mean that airliners can’t glide well, the Gimly Glider and Air Transat flight come to mind. But gliders can definitely beat an airliner in terms of performance.
You are, of course, correct, and thanks for clarifying.
Re: (2): There's a difference between sailplanes and gliders. Sailplanes are gliders that can “soar”, i.e. gain altitude just from the air that is moving up for some reason. Your friends have licence that says „Sailplane Pilot Licence”, not „Glider”.
The distinction is less pronounced nowadays, because there is no mondern aircraft designed as gliders-but-not-sailplanes, but historically there were planes that fit this niche, mostly military transport of WW1 and WW2 vintage.
Passenger jets (with engines turned off) are relatively decent gliders, but incapable of soaring. So no, you can't get more that about 20:1 glide ratio no matter how good is the weather (for sailplanes).
Regarding the turbofan and [0], above...if you're communicating to a non-engineer (me), how does the design get to the point of such complexity? I would love to learn the design story behind such an incredibly complex piece of machinery.
I am being serious, if you cannot tell.
For the same thrust it's more efficient to accelerate a large mass of air a small amount than t accelerate a small mass of air a large amount. The fan is what gives you that.
I rough guessed the cost of fuel over a 737's life as $150 million. Where the engines cost something around $30 million. That pushes the engineering economics towards maximizing the engines efficiency.
I'm suspicious that bypass ratio's for turbofans are close to maxed out. The diameter of the fan gets unwieldy. That was the design issue that the 737 Max was trying to get around. With bad results. Possible the future is hybrid designs with two engines and 4 or more electrically driven fans.
Yes, sorry, meant to write turboprop.
1 - a turbofan is a subset of jet engine, and there are no 738s running anything other than a turbofan.
Actually, nothing in civil aviation that has a "jet engine" has used anything but a turbofan (or turboprop) since the early 70s with the exception of Concorde and some older business jets.
(Turboprops are jet engines, too, to be precise, with the jet of exhaust gases powering the propeller.)
> Turboprops are jet engines
They are certainly turbine engines, but I thought "jet" was reserved for those engines that propel the vehicle solely by their exhaust stream and bypass air. I am willing to be told I'm wrong, though.
Turbofans are by your own definition jet engines. It's just that the bypass air is much larger.
I think you meant turboprop there, but the distinction I notice is that one has all propulsive airflow inside the nacelle, and one does not.
Agh. No, I meant turbofan, but I misread your post and actually completely agree with you - turboprobs are not jet engines.
Ha! It happens. Enjoy your weekend.
No, you don’t magically get the fuel back. But you do get a lot of the _kinetic energy_ back, and that energy keeps you flying without having to burn yet more fuel. You burn a lot of fuel while climbing, but then hardly any at all while descending. And that descent might cover 100 miles across the ground.
The 737-800 uses CFM56-7 turbofan engines.
[1] https://en.wikipedia.org/wiki/CFM_International_CFM56#CFM56-...
1) Yea, sorry, turbofan, not turboprop nor a jet.
2) It stays burned, but the energy is banked in potential energy of the aircraft, namely in a form of altitude. If you run out of fuel 5 feet above ground, you dont get to fly far. When you run out of fuel 35000 feet above ground, you can still choose where to land from multiple options.
3) huh? I dont get what you trying to say, but: Its always more economical to climb, and the faster the better. Ofc you cant climb too high when you intend to attempt to land in 5-10 mins, but nontheless, every feet gained is "banked", and the aircraft is more economical to run the higher you are.
4) I am not saying the winds arent a factor, and in no way I was arguing about how fuel reserves are calculated. My only claim is that: yes, by spending more fuel to gain altitude, you can then "glide" down almost for free later. Its not 1:1, because of constant losses like drag, but its being compensated by higher engine efficiency and less drag at altitude, that its always worth it to climb if you can.
There was a flight that was low on fuel diverting to alternate between 2 islands. The pilot panicked and chose slower climb to intuitively save fuel. They had to ditch the plane in water because of it - if they initiated full climb, they would have made the jump.
Wow this has a lot of replies!
Yes, you get a lot of the energy back, BUT there is a huge problem!
Large airliners incur a LOT of additional drag to slow down while landing. Some of that is entirely intentional, some is less intentional.
It is highly preferred to deploy the landing gear before touching down. Failure to do so may lead to a hard landing and additional paperwork, so airlines do not allow the captain to exercise their own discretion.
Extending the flaps maintains lift at lower speed, and higher flap settings allow even lower speed. The highest flap setting generally also deploys leading edge slats.
If the wheels of the airliner touch down and detect the weight of the plane then spoilers kill the lift of the wings, air brakes fully deploy, as well as thrust reversers.
All of these things add drag, which uses up all that energy you've been converting.
The upshot is that each landing attempt uses a LOT of energy, and you have to use fuel to replenish that energy after every attempt.
In other words, yes you get it back, but only for one landing attempt.
As someone who has ridden a bike up a big hill, and then down it, I don't think you get it back.
That is perplexing. Of course you get the potential energy back. It turns into kinetic energy as you descend. That is why you need not pedal downhill, and often even need to brake to prevent the bike from speeding up too dangerously.
> often even need to brake to prevent the bike from speeding up too dangerously.
Indeed, which is what the airplane would have done on its way down to land. So it's more like riding the brakes on your way down the hill, and now at the bottom when you realize you need to abort the landing, you are at low speed and it's quite an exercise to get back uphill to try again
100%. You are correct on that. You can’t use your kinetic energy to go around after a landing attempt.
But not because “you don’t get the energy back”. (As recursive suggested about a downhill bike ride which is the part i am disagreeing with.) You do get it back, but because you want to land you bleed it away to drag. And once it is bled away you don’t have it anymore.
So we don’t disagree about the practical implications for flying. I’m disagreeing with recursive’s particular statement about downhill cycling and what it implies about the physics of the problem.
The glider guys would always suggest a forward slip. It's a lot of fun to do. It's not taught often enough during primary training for powered airplanes.
Aren't low-speed slips something that makes planes flip upside-down when not used very carefully? (Inadvertent rudder changes corrected with opposite aileron resulting in a snap roll.)
A cross controlled stall can result in a spin (which is probably what you mean by flip upside down). The rudder changes aren't inadvertent, they're intentionally opposite the aileron input - the goal is essentially to fly somewhat sideways, so the fuselage induces drag.
In general forward slips are safe, but yes you have to make sure you keep the nose down/speed up. There's little in aviation that isn't dangerous if you aren't careful.
Yes, being that one is cross-controlled they must be used very carefully. It's really obvious that one is cross-controlling. It's the only time outside of really powerful crosswinds that you see what's below and ahead of you out of the side window. That view is what makes it fun.
You're probably thinking of a skid, which is when you put too much rudder in the same direction as the ailerons. Then the lower (and slower because it's on the inside) wing stalls first (and goes lower still) and away you go. Often when turning to land, so there's not enough altitude to recover.
Yes, but that also doesn't get any energy back on descent, quite the opposite, that is "riding the brakes on your way down"
Well it's not all lost otherwise it'd be a stall spin accident caused by performing the maneuver with too little airspeed. And that's hard to do. It's a noisy maneuver, the air slamming against the fuselage makes itself heard. Once performed it's not easily forgotten.
More dangerous than inadvertently spinning with too little airspeed is the possibility of shock cooling when relying on a forward slip for too much altitude loss. It really does need to be well-controlled.
I thought this topic was about energy gained and lost during a go-around. If velocity was V and altitude was H before the go-around, and velocity and altitude are again the same V and H after the go-around, then it follows that all the potential energy that was accumulated during the go-around (from converting fuel into altitude) has been dissipated (lost). Otherwise V would be higher the second time.
The subtopic changed from energy gained during descents to descents in general
Imagine a hill with 500 feet of elevation descent, followed immediately by 500 feet of ascent. No curves.
If you coast all the way down the first part, you'll get about 20 feet up the other hill before you need to start pedaling. This is a direct analogy to "getting your energy back" by losing elevation.
That is exactly what a rollercoaster does and it doesn’t start “pedaling” after 20 feet. Of course real systems have losses and you can’t practically use all the energy.
But you don’t have to believe me. Look at the video of this glider doing an unlicensed airshow: https://youtu.be/QwK9wu8Cxeo?si=L-0Mfmu8wk1ZlQU7
It is a glider so it can’t “pedal”. You can see it steeply descending from 5:13 to 5:30 while it is speeding up and then the pilot picks up the nose and trades some of his speed for elevation again. And then he does it again around the 7 minutes mark.
You have two buckets of “water”. One bucket is kinetic energy and the other is potential energy. You can trade one for the other. You can also “lose” from the total volume of “water” due to drag (or friction in the case of the bike or roller coaster). Or you can add more “water” to your system by pedaling or thrusting with your engines. This is just simple physics 101. Also simple lived experience if you ever have the opportunity to fly an airplane.
The more water you put in your system the leakier your buckets get. Drag is not linear with speed. That was my point.
This is because bikes cost you about 50% more energy going uphill than walking[1]. You get back everything you don't lose from having to pedal too slowly, hunch over the front wheel, and maintain constant torque on the pedals.
1: https://pedalchile.com/blog/uphill
Just as with bikes, it will depend on how slow it is descending. On "right" trajectory engines could technically be basically idle, and you save fuel flying high so it might not be all that huge loss.
No, and you don't want it. You want to be on the ground and stopped. In the lowest energy state.
It's not currently feasible to harvest it into fuel. It's (very very nearly) all lost to drag, on purpose.
How? On descent you can trade some of your altitude (potential energy) for kinetic energy, but then you can’t land the plane. For descent on an approach you’re going from low energy to even lower energy. In emergencies and with enough runway you can futz around with this some, but wiggle room on an airliner is not great, negligible to what will be expended on a go around.
Some of it. The air density is an important part of efficiency at higher altitudes, so every moment spent under like FL320 is wasted fuel.
So the entire climb "up", you are also wasting energy fighting the thick air. On the way back "down", that air again fights you, even though you are basically at idle thrust.
Your fuel reserves are calculated for cruise flight, so time spent doing low altitude flying is already at a disadvantage. "Two hours of reserves" is significantly less than that spent holding at a few thousand feet. Fuel efficiency while climbing is yet again dramatically worse
The problem isn’t getting the energy back, it’s doing so more slowly than gravity. Planes are somewhat limited in their ability to glide.
Some of it, but much is lost to drag. They do have to limit speed at all times.
Not really. While you have a large potential energy buildup at a higher altitude, you cannot "bank it" / "save it" on descent. There is no way to store it in batteries or convert it back into fuel.
One of the challenges of aeronautics is the efficient disposition of the potential energy without converting it all into kinetic energy (ie speed) so that the landing happens at an optimally low speed - thus giving you a chance to brake and slow down at the end.
> "While you have a large potential energy buildup at a higher altitude, you cannot "bank it" / "save it" on descent. There is no way to store it in batteries or convert it back into fuel."
An electric fan aircraft absolutely can recharge it's batteries on descent. The fans simply act as turbines, creating drag to slow the aircraft and electricity to charge the batteries. Large commercial airliners already have a small turbine that works this way, the Ram Air Turbine (RAT) which is used to generate electrical power in emergencies.
You can use a turbine to generate electricity, so yes, you are converting potential energy into electrical potential. However, no real mass produced passenger plane today can use that electricity for flight (thrust).
RAT is only used when sh*t hits the fan. Even then, it can help you power some hydraulics / electrical, not “store” energy for further flight.
The OP asked - in a low fuel situation, can the energy spent on a climb get effectively recovered - and the answer is not really. We convert as much as we can into unpowered (low-powered) descent. But once you are at a spot where you make a final decision to land or not, you are by design low and slow - and all that energy you had 15m ago is gone.
If you need to keep flying, those engines need to spool back up. And that takes fuel.
> "no real mass produced passenger plane today can use that electricity for flight (thrust)"
Such aircraft do exist. For example, the Pipistrel Velis Electro trainer. And more recently, the Rhyxeon RX4E became the first electric aircraft to be type-certified for commercial passenger operations.
It's likely that we'll see many more electric fan aircraft in the coming years/decades, whether powered by batteries and/or hydrogen fuel cells, or hybrids with both conventional turbofan and electric propulsion in order to improve efficiency and environmental performance.
> RAT is only used when sh*t hits the fan.
Isn't it when air hits the fan, technically?
(Sorry.)
> As others have said, final fuel reserves are typically at least half an hour, and you shouldn't really be cutting into them.
This is one of the multiple layers of defense that airlines employ. In theory, no one single failure should cause a major incident because of redundancies and planning. Airlines rely on the "Swiss-cheese" model of safety. Each layer has its own risks and "holes" but by layering enough layers together there should be no clear path between all of the layers. In theory this prevents major incidents and given the commercial airline's safety records I'd say it works pretty fucking well. Landing with minutes of fuel left should be exceptional. But it also shouldn't be fatal or a major risk due to the other layers of the system. ATC will move heaven and earth to land a plane low on fuel or with engine trouble safely. And everyone else in the system having 30+ minutes of extra fuel gives the space for this sort of emergency sorting.
I think this also reflects on the "efficiency" that MBA types bring to companies that they ruin. If an MBA sees a dozen landings with an extra hour of fuel, their mind starts churning at saving money. Surely an hour of extra fuel is too much and just wasted. Wasted because every extra gallon of fuel you take off with is extra weight you have to carry throughout the flight. Surely things would be more efficient if we could make sure planes only carry enough fuel to make their trip with very minimal overhead. And when everything goes perfectly according to plan, these decisions work out fine. Money is saved. Bonuses are paid. But the inevitable always happens. That's why it's called inevitable. Lives are lost. Wrists are slapped. Some people at the bottom lose their jobs. The world moves on.
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I thought a lot of airlines had rules to limit the number of attempts you could make at a single airfield in an attempt to prevent this exact kind of situation.
It sounds to me like they tried harder at their intended destination than maybe they should have, followed by going to an alternate airport that probably wasn’t a good choice in the first place, and then having to divert to the final airport where luckily they could land in time.
Interesting. To me it does not really make sense to think in terms of fuel left because, no matter the reserves, there can always be a situation so unlikely, so outside the ordinary, that it will drain all fuel reserves before you make it to the planned destination.
I have no clue how else to think about it though.
So maybe the thing we can improve is an understanding of likelihood?
I.e. prevent the journey from occurring if weather conditions are likely to be adverse above a certain threshold?
I'm not an aviation expert, but generally in safety engineering, safety buffers are not simply calculated as [normal situation] * [safety factor], but [worst case scenario] * [safety factor]
If you ever cut into your safety allowance, you've already fucked up. Your expected design criteria should account for all use cases, nominal or worst-case. The safety factor is there for safety, it is never intended to be used.
This is really helpful and I think I understand now.
The approach is basically “accounting for everything that might go wrong to the best of our experience, including problems arising from the complex interactions between the airplane and supporting ground systems and processes, this is how much fuel you need in the worst case scenario. And now lets add more to give us a cushion, and we will treat consumption of this last reserve as tantamount to a crash.”
Precisely.
This is exactly how it is in this case. Any consumption of the fuel reserve would result in an investigation, this is a very extreme case and it may even result in a change in the rules depending on the root cause.
Yeah idk people debating about this, if this justifiable then its all gucci and world can learn from such experience
Yes, exactly. The day it's normal to eat into the allowance is the day we start seeing planes falling out of sky for lack of fuel again. The only way to prevent that is to treat 30 min of fuel as seriously as you would 0 minutes.
Yes. Similarly, safety needs to be there even after the aging of materials over product lifetime. So basically when aging is the only variable to be considered end of life date is the worst case scenario.
"I’m a little confused by what there is to investigate at all."
You're confused why they should investigate how everyone on that flight came within minutes of dying?
Something about the fuel reserves, procedures, or execution was clearly flawed.
I think the argument is that this is precisely the tail end of exceptional conditions overfueling is designed for. If it's typical to fill fuel for 4 hours on a 2 hour flight, and the flight took 4 hours. It seems like this is exactly why they overfuel to 4 hours. If this happens once every 100k flights, then it doesn't even beg the question of "why aren't we overfuelling to 4.5 hours".
This is just clarifying the question from the perspective of an outsider.
That said, an investigation would be pretty reasonable, even if only to confirm that the abornamlity were forces majeures
> If this happens once every 100k flights, then it doesn't even beg the question of "why aren't we overfuelling to 4.5 hours".
- This does not happen once every 100k flights. That's once per day
- If this were happening once every 100k flights we would be adding another half hour to the reserve tomorrow.
Although credit is due to fuel reserve policies considering they landed after two diversions and three go arounds.
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Why not? It's a factual report stating that the AAIB has opened an investigation into a potentially dangerous incident. There's not any editorial bias evident. See other extensive comments as to why this is not just a case of "it landed, so what's the problem?".
Sensational headline completely missing the point.
Or did it work as intended? The plane had multiple failed landing attempts, was re-routed, and had enough fuel to land safely. While no one wants to cut it this close, this was not a normal flight.
I’m not an expert in this field, but it would seem that the weight of extra fuel would increase operating costs, so it’s is effectively insurance. How much extra fuel should be carried to account for unplanned events like this, while not carrying so much that it becomes cost prohibitive.
Fuel depletion is risky, but not that risky; see the Gimli Glider for a case much more dangerous than this, which still worked out amazingly well.
Edit: Here is the Wiki on incidents... https://en.wikipedia.org/wiki/Fuel_starvation_and_fuel_exhau...
That example is so well known due to how exceptional it was, especially how the pilots handled it. Robert Pearson, the captain, was a very experienced glider pilot. That's something that not many commercial pilots have.
There were also two factors in the landing, that allowed for this to happen. You're going to be coming in really fast for a landing, when gliding in a commercial jet, and you don't have access to your thrust reversers to slow it down. There was a repurposed runway, that they used to land, that just happened to have been used as a drag racing track and had a guard rail. They were able to slow down by scraping across that. It also just so happened the nose gear didn't deploy fully so scraping the nose of the plane against the ground also helped slow it down.
Needless to say it was a bunch of very fortunate events that allowed it to not end in disaster. In any case I would consider it very risky.
And even with all that scraping damage they were able to fly the plane out, repair it, and put it back in service. Amazing.
The "scraping helped slow it down" theory makes no sense to me. What do you think has a higher coefficient of friction - tire rubber on asphalt, metal on asphalt, or metal on metal?
I would hesitate to chalk it up to just theory, given it was in the NTSB report and they don't really mess around with throwing baseless stuff around. I'd be interested to take another look at it. They likely go into the material science and physics behind this very thing. They're usually filled with gems.
You also have to keep in mind, it wasn't just rubber against asphalt, it was rubber on a wheel that spins. I'm not sure if the front nose gear on a 767 has any brakes but even if it did, I can't imagine it would be sufficient at the speeds they were going.
They could have died. The nosewheel assembly being pushed up through the floor of the cockpit has killed more than one pilot.
I mistyped, as this was Canada it wouldn't be the NTSB but the Canadian equivalent at the time: Canadian Aviation Safety Board. The report is a good read.
Don't forget the surface area of contact...
Rubber likely grips much better than metal, however three wheels have massively lower surface area than the body of the plane, or even a small section of it like the head.
Of course we don't land tireless for other reasons (metal transfers heat exceptionally well unlike rubber, paint doesn't survive high speed impact, and it tends to deform upon impact with anything, making any future flights unsafe), but the fastest way to slow down if you don't care about safety or comfort would probably be to land tireless, if you could introduce some rotational spin, that might be faster (more force directed in multiple directions).
Also, on the note of "coefficient of friction", remember that this number is not just some innate property of a molecule - as the metal scratches the pavement and deforms, its coefficient of friction goes up as micro-deformities accrue.
You seem to be assuming those are "or" rather than "and"
Fuel depletion is stupendously risky, it is one of the most risky things that can happen to a jet. The only things more dangerous are fire and control systems failure.
The Gimli Glider was a case of many items of luck lining up.
You could've read at least the Wikipedia page on how miraculous Gimli Glider was.
From "all engine failure is never expected and not covered in training" to "Pearson was an experienced glider pilot familiar with techniques rarely needed in commercial flights" to the amount of maneuvers they had to execute on a barely responding aircraft
Exactly, the takeaway from that saga is that extreme luck does happen, not that flying without fuel is perfectly safe.
They also happened to know about an old airport which was no longer active, but did not know about the concrete barrier in the middle.
I know you're trolling, but for anyone that hasn't heard of Gimli Glider, look it up or watch a documentary on youtube. The stars definitely aligned to make that happen.
Depends largely on the altitude when fuel runs out. If it runs out when they're at 4,000 ft and it's windy, it's probably game over.
Fuel depletion is _not that risky_ is an interesting take. But hey, it won Chapecoense its first and only Copa Sudamericana, so maybe it isn't that bad after all?
https://en.wikipedia.org/wiki/LaMia_Flight_2933
And what happens if you're not at 40k feet when the fuel runs out?
Good thing that airliners spend so much time at altitude!
Especially while making landing attempts?
Depends if our goal is to have zero aircraft crashes. If the goal is zero, then for any given parameter, you have to define a margin of safety well before crash territory and treat breaching that margin as seriously as if there had been a crash.
Similarly planes are kept 5 nautical miles apart horizontally, and if they get closer than that, you guessed it - investigation. Ofc planes could come within inches and everyone could live, but if we normalize flying within inches, the we are also normalizing zero safety margin, turning small minor inevitable human failings into catastrophe death & destruction. As an example, planes communicate with ATC over the radio and are given explicit instructions - turn left 20 degrees, fly heading 140 etc. From time to time these instructions are misunderstood and have to be corrected. At 5nm separation everyone involved has plenty of time to notice that something was missed/garbled/misinterpreted etc and correct. At 1 inch separation, there's no such time. Any mistake is fatal, even though in theory you are safe when separated by 1 inch.
TBC an investigation doesn't mean investigating the pilots in order to assign blame, it means investigating the entire aviation system that led up to the breach. The pilot's actions / inaction will certainly be part of that, but the goal is to ask, "How could this have been avoided, and ask how every part of the system that we have some control or influence over might have contributed to the outcome"
We shouldn't aim for 0 crashes due to low fuel though. How many deaths does carrying around 3x fuel than what you reasonably need contribute to via extra pollution?
We should aim for 1 every 10-100 years or something reasonable like that.
We should account for deaths from pollution, but if we are going to do that, we should be willing to do that for 99% of aviation fuel that has nothing to do with reserves & safety margins, in addition to fuel used to drive cars.
Any regulation short of "carry infinite fuel" will be a trade-off, and entail some risk and anyone involved in setting these knows that. Zero may not be our actual target or even possible, but it is a useful aspiration to ensure that everyone is pulling in the right direction.
We dont aim for 0. Zero means dont fly. one in every 100 years globally for all flights would be very safe.
On the contrary - commercial aviation does aim for perfection.
At 3x the number of deaths would be 0 because there would be no more flights.
Well imagine they had to do a go-around on that landing. Go-arounds are extremely normal and might be done for a million reasons; your speed is wrong, your descent rate is wrong, your positioning is wrong, there's bad wind, there's an issue on the ground, etc etc etc. Six minutes of fuel is really not enough to be sure that you can do a go-around. So now, if ANY of those very normal everyday issues occurs, the pilot has to choose between two very bad options: doing a go-around with almost no fuel, or attempting a landing despite the issue. That's just way too close for comfort.
Aviation operates on a Swiss cheese model; the idea is that you want many many layers of safety (slices of cheese). Inevitably, every layer will have some holes, but with enough layers, you should still be safe; there won't be a hole that goes all the way through. In this case, they basically got down to their very last slice of cheese; it was just luck that the last layer held.
I think he would attempting a landing despite the issue in most cases because running out of fuel during go-around would be worse.
>I’m a little confused by what there is to investigate at all.
One of the most important aspects of taking safety seriously is that you do not just investigate things which had an impact, but that you proactively investigate near misses (as was the case here) and even potential incidents.
A plane with 6 minutes of fuel left is always a risk to every person on board and potentially others if an emergency landing becomes the only option.
Indeed that is the definition of a "aviation incident" where there was a risk of injury or damage. If there is actual injury or damage it becomes an "accident".
The investigations into incidents aren't usually particularly long or noteworthy and often the corrective action will be to brief X on dangers of Y, or some manner of bulletin distributed to operators.
If you cut into the final reserve, it’s a full-blown emergency requiring a mayday call.
This should not happen. So what’s there to investigate? How it was allowed to happen, and how to prevent it from happening again.
EDIT: it’s a mayday even earlier than that. It’s a mayday once the pilots know that they WILL land with less than the final reserve.
If they have to touch and go, how long would it take until they get the plane around for another approach? In fact, you might not get as far as that touch and go and have to go around. You need some margin for all of these eventualities. The likelihood is low that these happen, but they have to be accounted for.
Sure, but the flight was a lot longer than planed. How much extra do we need. They declared an emergency, and thus put themselves at the front of the line. They had 6 more minutes to do that touch and go around if that happened, and since they were already in a low fuel emergency they get priority and so there is enough time to do that if they needed. (edit - as others have noted, 6 minutes with high error bars, so they could have only had 30 seconds left which is not enough)
They landed safely, that is what is important. There is great cost to have extra fuel on board, you need enough, but it doesn't look to me like more was needed. Unless an investigation determines that this emergency would happen often on that route - even then it seems like they should have been told to land in France or someplace long before they got to their intended destination to discover landing was impossible.
> They had 6 more minutes to do that touch and go around if that happened
6 minutes is way out of the comfort zone. They might not have made it in that case.
Correct, article says they landed with 220kg which is around 6 minutes of average fuel burn over an entire flight - bit less at cruise, a hell of a lot more at takeoff/climb.
So I don't think 220kg is enough to do a go-around in a 737 (well, a go-around would've been initiated with a bit more than 220kg in the tank - they burned some taxing to the gate - but you get my point.) I've read around 2,300kg for takeoff and climb on a normal flight in a 737-8. A go-around is going to use close to that, it's a full power takeoff but a much shorter climb phase up to whatever procedure is set for the airport and then what ATC tells you.
I just flew 172s but even with those little things we were told, your reserve is never to be used.
These people came very, very close to a disaster. Fortunately they had as much luck left as they did fuel.
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That’s about as useful as opening a fortune cookie and reading it off as an answer.
Straight from the horse’s mouth: https://web.archive.org/web/20230630013840/http://www.boeing...
In the first table they list 2307-2374 kg of fuel for takeoff and climb.
You’re talking to the wrong horse though.
Isn’t a 737-8 the max 8 variant? It uses newer dual CFM LEAP-1B engines. How does it compare? I can’t really find the data. The spec you’re referring to is for the older 737-800.
Another fortune cookie:
https://www.aircraft-commerce.com/wp-content/uploads/aircraf...
It suggests an overall savings of ~14% over the 737-800 but doesn’t look at specific takeoff/climb comparison.
I wasn’t posting the LLM output as a source of truth. I was just using it to question the uncited value. And I still really don’t know the answer. If you’ve got another data source I’d love to get it.
Why do people keep insisting on pasting LLM output to HN when every time it happens, it gets downvoted to oblivion? The community clearly doesn't want it. If we wanted to know a computer program's opinion about something, we could ask it ourselves.
I was using it to question that exact stated fuel consumption number without a citation. For hard data (like fuel consumption) getting a value from an LLM isn’t absurd.
If not absurd, it's very poor form. You should never use LLM as input for a discussion, nobody wants to hear that. Use it to search for authoritative sources.
It’s fine if you post an actual citation that you might have found through the LLM. Just posting AI slop is worse than useless, though, and also unpleasantly dystopian.
ok, how do we verify that?
Maybe he should ask Claude next.
That’s the point? I wasn’t suggesting it was correct. Just that the value is wildly different from their own non-cited number. The next stage was to get a citation from an actual datasheet. Their reasoning was nothing beyond “I’ve read”
I agree, well out of comfort zones. However to my reading multiple different things went wrong to get to this point.
That could be. We just don't know right now, but your intuition may well be correct, even if there is a single root cause there could very well be multiple contributory causes.
They failed to land at two airports before the third. I can't say if they made the right decisions but that already is two failures.
Go arounds are not failures.
They are expected situations, but still a failure of the original plan.
They are not a failure of the original plan, they are a mandatory component of the original plan that if everything is nominal never gets executed. Every pilot on approach is ready for one or even more go-arounds and they happen quite frequently for a variety of reasons.
They happen a few hundred times per day at ~100 k flights.
How much extra do you need? Enough that a pilot/crew doing their job properly will never run out of fuel and crash.
So yes they will do an "investigation". It's not a criminal investigation. It's to understand the circumstances, the choices, the procedures, and the execution that ended with a plane dangerously close to running out of fuel.
This will determine if there were mistakes made, or the reserve formula needs to be adjusted, or both.
Don't tell me about cost, just stop. Let MAGA-Air accept some plane deaths to have cheap fares.
With 6 minutes left everyone could have died if anything went wrong with the final landing, even a gust of wind could have ended everybody's life.
Could have, but pilots practice no fuel landings all the time (in simulators). If they can get to ground that is "level enough" nobody dies. It is not something you ever want to see in the real world (and in the real world people often do die when it happens), but it isn't automating people die.
I don't think that's all that true for airliners. Pilots definitely practice for engine-out scenarios during all levels of training up to the airlines, but the ability of a plane the size of a 737 to safely land on anything but a runway is...limited. And if you're low, slow, and trying to go around, that's not a lot of time to glide to ground that is "level enough".
i didn't mean to imply no runway landings. Landing on grass is questionable. They would practice water landings though
Those landings are practiced from a reasonable altitude.
Surely the issue is more that they decided to make so many attempts to land local. There should be a max level of attempts.
There is a lot of pressure on pilots to land local. But 3 go-arounds happens, not often, but it does.
Perhaps that decision needs to be removed from the airline and there needs to be an independent decision maker there.
Pilots are ultimately responsible for the aircraft, that's pretty much set in stone but if ATC would tell them to divert they would unless there already was an emergency.
There is a max level, and it is three.
This reminds of discussions following the Fukushima disaster where one commenter claimed that it wasn't a design flaw, because it was an extraordinary circumstance. I found this appalling, because I do not at all think that was the risk profile that was sold to the public; I think people believed that it was supposed to be designed to safely survive 1000-year earthquakes and the tsunamis that they create.
Likewise, I think that the flying public is lead to believe fuel exhaustion is so rare that when airlines are compliant with regulations, no such disasters across all flights across all carriers will occur during your lifetime.
It's also a communication problem, because labels like "100-year/1000-year event" are easily misunderstood.
* they're derived from an estimated probability of the event (independently) happening each year. It doesn't mean that it won't happen for n years. The probability is the same every year.
* the probabilities are estimates, trying to predict extreme outliers. Usually from less than 100s of years of data, using sparse records that may have never recorded a single outlier.
* years = 1/annual_probability ends up giving large time spans for small probabilities. It means that uncertainty between 0.00001% and 0.00002% looks "off by 500 years".
https://practical.engineering/blog/2025/9/16/an-engineers-pe...
I find a useful exercise is to have a cheat sheet of historic flood heights in some area, tell someone the first record high, ask them how high they would make the levee and how long they think it would last. Peoples' sense for extremal events is bad.
That's a great exercise. Where I live a lot of people died because in the past we were not able to make that guess correctly. A lot was learned, at great expense.
I'm sure we can all remember at least one person in any situation who will say something we find memorably awful.
6 min, is empty, 6 min is purely theoretical, 6 min would not clear for ground handling or a test start, or a fuel system check,6 min would not do a go around. will interesting to see if they release info about what the real amount of fuel left is, and an authorative discussion on how much useable flight time was there. did they actualy make the taxi to the terminal?, or run out on the apron?
I think the article says that someone saw 220kg written on a log - that's about 6 minutes worth at cruise. So yeah, it's zero basically.
Yes. There is another comment above making light of the 6 minutes as if another go-around was still an option, that is a ridiculous take. They were going to bring that plane in and land it no matter what on this last run, otherwise they'd crash for sure. 6 minutes may not even be within the margin of readout.
By your logic you need an infinite amount of fuel.
If you define X the amount of fuel you need after you land.
And you say that X needs to be enough to make an emergency landing.
And we define that the amount of fuel required for an emergency landing should cover the amount required for the landing operation while still having X in the tank when landed.
X > X + landing_cost
The plane already had made 3 failed attempt before and was redirected to two different airports.
Naively as an outsider, this situation seems like everything worked as intended?
I don't remember all of the rules off the top of my head, but if you are ever landing with less than 30 minutes of fuel, something has gone seriously wrong. You are required to take off with sufficient fuel to fly to your destination, hold for a period of time, attempt a landing, fly to your alternate, and land all with 30 minutes remaining. If you are ever in a situation where you may not meet these conditions, you are required to divert immediately. In choosing your alternate, you consider weather conditions along with many other factors. This was, without question, a serious emergency.
From the very brief description in the article, I would say they should have diverted to Manchester at least 25 minutes sooner than they did. I will include the GP's caution, however:
I'd be very wary to get ahead of the investigation and make speculative statements on how this could have happened, the one thing that I know for sure is that it shouldn't have happened, no matter what.
If you are ever in a situation where you estimate you will land with less than 30 minutes of fuel, you are legally obliged to declare a MAYDAY. One of the few situations where a mayday is legally required.
My understanding is that they shouldn't have spent that much time in the air (not intended as a guess for the cause). The margin is there for situations where you can't land earlier, not the margin for scheduling the landing. There is margin for expected potential delays, they were in the other margin that should never be used except in true emergencies.
Oh I think I see; so is the question not “why did they land with so little fuel”, but more like “why did it take so long to decide to redirect to a known-safe airport”?
Possibly. Or 'why did your fuel readings deviate from what was actually in the tanks' or 'why did we leave with less fuel than we thought we did' and so on. There are so many variables here speculation is completely pointless. All we know is that something went wrong, that it almost led to a crash and that it involves an airline with a very good record when it comes to things like this.
Low fuel happens, but this is (very) exceptional.
I don't know. As the parent said, I'd be careful with guessing the root cause right now. They should not have been this low even if diverted due to weather.
By asking such a question you understand the need for an investigation
>One pilot who reviewed the log said: “Just imagine that whenever you land with less than 2T (2,000kg) of fuel left you start paying close attention to the situation. Less than 1.5T you are sweating. But this is as close to a fatal accident as possible.”
Thirty minutes.
If at any point you expect to touch down at the nearest safe airport with less than 30 minutes of fuel remaining, you are required by regulation to make a mayday call.
Mayday is a term enshrined in law. It is only to be used when people will die if you do not receive help. In the US, calling it inappropriately can be punished with up to 10 years in jail and a $250k fine. It's protected in this way because as soon as you call mayday, in many situations there are actions that must be taken by law or regulation. Other appropriate uses include things like "our plane is on fire" or "our wing just fell off and we can't steer the plane".
As soon as you think you can't land with the fuel reserves you are _required_ to call mayday, other pilots are _required_ to clear the radio for you, and ATC is _required_ to provide any and all supported possible until you're on the ground.
The investigation is not to figure out who to send to jail or something. The investigation is because a flight just came this >< close to having hundreds of people die. That fuel is there as a safety margin, yes. That's how everyone ended up walking off this plane instead of dying as the plane was ripped apart by some trees somewhere. That is good.
But air travel did not become as safe as it with an attitude of "this hasn't killed anyone yet, all good". The fact there was an incursion into the safety margin should not be looked at as "eh, working as intended" but "holy hell we just came this close to disaster, what went wrong that almost killed all these people? how do we stop that happening again?". That is what an investigation will be looking to figure out.
To put it in vaguely IT terms, this is something like... your application has started corrupting its database, but you have _a_ backup copy. On one hand, you can think "eh, we have a backup, that's what it's there for, who cares". On the other you can go "holy shit, any time we need to restore from the backup we narrowly averted disaster... how do we make sure we're not in that situation again?". The former is probably going to lead to irrecoverable data loss eventually. The second will have you addressing problems _before_ they ruin you.
What is fascinating about this whole discussion is that the general world of software development is so far away from actual engineering that all of these basics require painstaking explanation.
5 9's uptime in aviation means one airliner crash a day.
> If at any point you expect to touch down at the nearest safe airport with less than 30 minutes of fuel remaining, you are required by regulation to make a mayday call.
From the article, they did issue a mayday call, when the closest airport was presumably Edinburgh. Then they flew to Manchester and landed.
There must have been a very good reason to do that.
Only issue I see is that should there have been stricter rules to diverting way earlier. If winds were such as to make landing harder. Would just directly going somewhere else been the correct choice to force.
It also sounds like they went to an alternate airport they probably shouldn’t have bothered with.
Well, if you know you're pretty low on fuel, you are likely to pick an airport where the weather is good, rather than risking three more missed approaches at a closer one where the weather is probably also bad.
Of course, Manchester is also a Ryanair base. There are two Ryanair bases closer to Prestwick (Edinburgh and Newcastle), but maybe the weather was bad there too? If the fuel situation was so dire, questions might be asked during the investigation why they didn't pick a closer airport with good weather that wasn't a Ryanair base (if one existed), but ultimately it's the pilots' decision to fly a bit further to an airport they are familiar with, and second guessing them with the benefit of hindsight is probably not a good idea...
They made two attempts to land at Prestwick, then diverted to Edinburgh (which also had bad weather). After one attempt at Edinburgh, they then diverted to Manchester.
This is likely one of the questions the investigation will focus on.
If you get shot, but had a bullet proof vest on, and hence didn’t die, technically everything worked as intended.
Personally, I’d still want to figure out why I got shot and work on making sure that didn’t happen again.
Especially if you basically got shot multiple times (for an analogy in this case).
> I’m a little confused by what there is to investigate at all.
So because the safety margin still worked while down to near vapors we should conclude there's nothing to learn for the future to reduce the risk of similar incidents?
That's certainly... a take.
Flight from Edinburgh to Manchester is just a bit more than 1 hour, so after trying 2 landings, diverting to Edinburgh (15-20 minutes flight), 1 more landing attempt, well, you get very close to 2 hours.
I felt like that seems a little long from EDI to MAN (after all, EDI to LHR is typically a flight time of under an hour!), so:
https://globe.adsbexchange.com/?icao=4d2256&lat=54.720&lon=-... is the track of this flight.
Went around at EDI at about 19:10Z, landed at about 19:51Z, so about a 41 minute flight.
Right, I probably got the information for flight time as seen by a passenger on a ticket, not for a plane already flying. Thanks!
Similarly naive outsider, but I've read things here and there. My understanding is that they should have declared mayday (emergency) and landed (potentially at another airport, potentially in the middle of nowhere) _way_ before so that when they have landed they still had 30 minutes or more of fuel in the tanks.
Whether it can be prevented in the future. Should planes fly with even more reserve fuel? It's possible. Or maybe different ways of selecting alternate landing sites?
It may even be the answer is "no, everything went as well as it possibly could have, and adding more reserve fuel to every flight would be unacceptably wasteful, so oh well", but at a minimum they'll probably recommend even more fuel on certain flights into risky weather.
Imagine you're standing on a balcony and discover that the supports are cracked almost all the way through.
Do you shrug and say, that's why they have a safety factor, everything worked as intended? Or do you say, holy crap, I nearly died, how did this happen?
The purpose of the safety factor is to save you if things go badly wrong. The fact that it did its job doesn't mean things didn't go badly wrong. If you don't address what happened then you no longer have a safety factor.
I think a more insightful answer is how often is it acceptable for the reserves to actually be cut into. If this was happening often, then there’s a likelihood of a future disaster. As it is there is 1 isolated case that still ended with a positive outcome. I think it almost adds support for the current reserve levels to be pretty dialed-in.
Officially: never. Unofficially, a minute or two would be cause for concern and the regulators would most likely be showing an interest. The airline may have a higher margin than the official one. This is exceptional, they were within the margin of error on readout and the pilots must have known that. It's one thing to know you have half an hour of fuel give-or-take in the tank it is another to know that give-or-take you are running on fumes.
The answer is 'never' as the reserves are only added for worse-than-worst case scenario, i.e. in this case something went literally unimaginably (as of then) wrong.
> How much fuel should they have landed with?
I think about 30 minutes worth of fuel.
Not knowing their flight plan, it could have been that Edinburgh was the first alternate and Manchester the second alternate.
Might not be about fuel but about why they even tried instead of diverting earlier.
Might even be 100% done by the book but book needs changing (tho I doubt that, it's not exactly first case of "a lot of bad weather")
Our definition of 'bad weather' is definitely changing as we gather more data.
Besides regular weather (which airliners aim to avoid except during take off and landing) there are many other factors at play here. There are several almanacs that are used for fuel calculations & navigation, they are updated annually.
The fastest jet stream (the aviation equivalent of the trade winds) recorded is north of 400 Kph, having that with you, against you or perpendicular to your flight path will have a substantial influence on fuel consumption and flight duration.
I agree with you that it may well end up with a regulatory change but that's one of many possible outcomes here. I will definitely keep an eye out for the report on this flight's investigation. It is going to make for very educational reading.
I dont know but maybe they should have diverted sooner. Maybe an hour into the flight?
30min+
Yes, I believe this is correct for this model aircraft.
ideally, enough to divert to another airport, in the off chance something happens, like a pending emergency at point post.
At what point should they investigate?
0 minutes?
-1 minutes?
Anything less than 60 minutes would be looked at by the airline, anything less than the legally required amount (30 minutes for a jet of this type iirc) will result in a very serious investigation. Note that for slower aircraft (for instance a turbo-prop) the time requirement goes up not down because they may have to spend more time in the air to reach an alternate (or secondary alternate, if things are really bad, like what happened here).
They should investigate after the first failed landing, regardless of the amount of fuel in the tank.
Go arounds are perfectly normal and are not a 'failed landing', a failed landing is a crash.
One of those YouTube channels where a professional pilot evaluates flying incidents had a similar incident when the pilot started yelling at the tower when they tried to make him go around again. He essentially said he would declare an emergency if he didn’t hear different instructions. I think he had 10-15 minutes when he touched down.
One of the things the reserve is for is if the plane immediately in front of you fucks up the runway, you now have to divert to the next airport. You need at least enough fuel to get there and for the tower to shove everyone else out of the way so you can make an emergency landing.
There are other reasons someone could abort a landing and have to go around again, besides debris in the runway. And sometimes two of them can happen consecutively.
In the case I’m referencing, it was pointed out that p the pilot made things worse by going faster than he was told to fly, using up fuel and also making him too close to a previous plane which forced him to go around the previous time, so it wasn’t all the tower.
Really? Equally as an outsider - it feels like one "go-around" and you're fucked.
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