She isn't "returning" the plane, she's landing it somewhere and he's finding out it's there later. And she isn't "fixing" it, she's replacing bits (the battery and headphones) he removed to make it harder to steal.

> she isn't "fixing" it

The idea of a rando doing unknown maintenance on my plane is downright horrifying.

suck it up, pal, I just repacked your wheel bearings

Well if it’s you I’m alright with it.

Apparently she sometimes returned the plane?

> As Hong would come to find out, the colorful aircraft had been flown across Southern California by an unknown pilot, unnoticed, in a series of joyrides — or joy flights — at least twice before and then simply returned to the airport.

That was my first thought. There's only so many places you can take it. Though I guess they could also ... hide it in a hangar somewhere?

But don’t all pilots have to lodge their flight plans? Surely hiding a plane in a hangar is not that easy since you would know which airport it is located in.

> But don’t all pilots have to lodge their flight plans?

No, they don't. And many municipal airports aren't even manned and, outside of certain areas, aren't under direct air traffic control. I flew in a Cessna with a private pilot who landed at a municipal airport in Los Angeles Country without ever talking to anyone. He just announced his intention to land on the published radio frequency, received no objection (because no one else was around), visually confirmed the runway was clear with a flyby, then lined up on the approach path and landed. I got the sense this is the norm in civil aviation outside of major airports.

Yeah I’ve had the same experience several times with a private pilot I knew. There’s a procedure for it in the pilot’s handbook.

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Yea, this is the norm.

No. Many flight types do not require flight plans.

https://www.ecfr.gov/search?search%5Bdate%5D=current&search%...

Or browse by Title 14, Chapter 1, Subchapters F & G (Aka Title 14, Parts 89 - 139)

I'm not vouching for this link in particular, but you can also search for things like Part 91 operator, Part 135 operator, etc

https://l33jets.com/resources/blog/the-difference-between-pa...

Although filing a VFR flight plan is an excellent idea so that someone is looking for you in case you don’t show up at your destination, it is optional. ATC receives IFR flight plans only; VFR flight plans go to Search and Rescue.

It's fairly easy to change a 12V battery, and is covered under elementary maintenance (the owner can do it themselves).