Ugh, there have been Cessna deaths caused the same way. It's my least favorite failure mode to think about, since there's no obvious way to correct. In a Cessna, best you can do is release the yoke and tiptoe on to the rudders, but professional instructors have still died when this happens to them, since low altitude errors are often not correctable by the time you've lost too much altitude.
Usually there ought to be more than one locking mechanism involved, though..?
Suppose your car seat hasn’t locked. You drive, then you suddenly go up a hill, and the seat slides back. Well, fine, you hold on to the steering wheel (or not), stop, take a breath, adjust the seat, and carry on.
Suppose your plane seat hasn’t locked. You taxi around to the runway (slow and always level), then you begin the takeoff run. Already, you have some acceleration pulling back. Then you gently pull back the yoke to rotate. Now, suddenly your seat slides back. You hold onto the yoke, stall, and die. Or you let go off the yoke, and now the plane is unpiloted in the crucial take-off phase. And, note, stopping is not an option at this point.
That’s why vigorously thrashing around in your seat is part of the before-takeoff checklist (“Seat - LOCKED”).
My wife knows of two fatal car accidents caused by this. Don't adjust your seat whilst driving peeps, and make sure it clicked into position before you drive if you adjust it.
Could be because people don't generally drive 40 year old cars! The aircraft in the first fatal link above was manufactured in 1979 and the seat failed in 2016; the second was manufactured in 1969 and crashed in 2014.
And because it would be less likely fatal in the car, so you'd be less likely to hear of it happening.
(Less likely fatal because car collisions are less fatal due to e.g. airbags, and less likely to impact terrain since it only takes a second to undo your car seatbelt, and because there's no pitch control to have messed up.)
My front driver's seat adjustment is all motorized - but not the passenger seat. Originally it annoyed me (the motors are so slow to move!) but now I'm wondering if it might be an intentional safety feature - it's never "unlocked", so you won't suddenly slide away from the pedals and wheel because a part failed to latch right.
If your car seat slides back unexpectedly, the most likely problem will be a decreased ability to press down in the accelerator. The seat would generally slide back only under forwards acceleration. Under braking the seat would slide forward giving positive pressure onto the brake pedal.
You would keep steering the car, while also attempting to unlock the seatbelt. Depending on the car, you could also activate the parking brake. (In my car, it's a button on the center console, and it can be activated at high speed and will provide emergency braking.)
"Serious" is still not the same as "fatal", even if your car hits something. If your plane stalls and falls hundreds of feet, my understanding is that the fatality rate is going to approximate 100%.