Other parts of the automatic transmission system fail, sure, but those parts are the same parts that are in a manual transmission. (Because, after all, in modern cars, a manual transmission's control system still ends up as signals sent to an electronic gearbox.)
So, like I said—in modern cars, where you've just got an electronic gearbox anyway, there's no sense in having both the ASIC issuing control-commands to the electronic gearbox, and a backup manual stick for issuing the same commands. If there's any fault in the system, it's far, far more likely to come from the stick's mechanism breaking down and issuing spurious commands, than from the ASIC breaking down and issuing spurious commands. And more likely than either is the gearbox getting messed up because it's sitting in a hot, dirty engine compartment.
In 2018, it is possible to have a car with an ECU that is 30 years old, and I happen to have one. Solder joints can go bad over time, and repairing the control unit is a thing that people do on cars like mine. If I was looking forwards regarding some other bit of electronics, I would probably worry about capacitors too.
Autopilot systems, however, are only as good as the people who program them. A helicopter, as mentioned elsewhere, is dynamically unstable and requires so many tiny inputs to maintain steady flight, let alone hovering. Just like in Teslas that 'nope' out of their Autopilot systems back to the driver milliseconds before a crash, a pilot has precious little time to retake control should the electronics fail.
Car ECU keeping your car moving in one dimension (forwards) - fairly safe to let a computer take over, minimal danger if it fails.
Autonomous technology keeping your car moving in two dimensions (forwards AND steering) - very complex, very little time to retake control in a failure scenario, very dangerous.
Autopilot keeping your helicopter moving in three dimensions - I think you get the idea by now :)
Either way, failure is not unique and can happen in either domain. There are plenty of examples of electronics failing and again it is strange to say that they don't. Silicon chips might not move but they are physical products that can overheat or short-circuit or just break.
Aircraft are much more critical than cars and the reason they have multiple completely redundant systems is precisely because things do fail all the time.
To be sure, it's not because they fail all the time, but to probabilistically address the risk that if Murphy does come knocking, consequences won't be immediately catastrophic.
I only meant to clarify that aircraft redundant systems exist because failure mode consequences would be catastrophic with unacceptably high probability otherwise; not simply because things in general fail all the time, as was asserted.
It's a subtle yet significant difference that other readers in passing may not recognize.
No, they don’t (so long as you are talking about stick-shift and not paddle shift).
That has more to do with aggregate risk management predominantly driven by predicted MTBF, failure mode analysis, and safety criticality levels.
Automatic transmissions fail all the time, and then the car stops moving. Ok for cars but serious problem for flight so these aircraft have multiple automatic and manual redundancies.
Helicopter autopilots are indeed full guidance systems like fixed wing aircraft, but they can hold the craft in hover position because it's just another flying position possible for helicopters, but it is still actively flying.