Re: 1 vs 3 - a story from the techncial diving world ....
I wondered that too. The GPS and Inertial nav systems can both provide a ground speed readout and with the airspeed data from before the pitot tube* fails can also provide a wind speed and direction.
To my mind what should happen if the pitot fails is the autopilot uses the GPS/inertial data to continue flying while alerting the pilot that he ought to get ready to take over. If the ground speed changes too much from what's expected with the last known wind and engine settings hand over to the meat sack.
This has the advantage of minimising the startle effect of the aircraft suddenly throwing you control and telling you what's wrong at the same time while your brain struggles to get up to speed.
*There are multiple on airliners but I'm not sure what the fallback logic is.
Biting the hand that feeds IT
