Originally Posted by
fernytickles
Thats assuming the automatic deployment system worked. Back up the back up systems ad infinitum.....
Consider this...
You've got 3 pitots giving constant readings that the computers check against each other for a disagree, like so:
A=400,400,400,400,400,453,750,896,345
B=400,400,400,400,400,400,603,342,533
C=400,400,400,400,400,400,400,400,400
X=-,-,-,-,-,-,400,400,400
where X is the standby pitot. As you can see, after the 5th iteration pitot A gives a differing reading, and after the 6th iteration both A & B pitots are giving differing readings. The computer is constantly monitoring the differences between pitots A,B,&C, and throws a 'disagree' at either iteration 5 or 6. This is where X is deployed and the computer can then take it's reading and compare it against each of the other pitots one by one to see if you find an 'agree' since the probability of 2 or more pitots agreeing is infinitely smaller than the probability of pitots disagreeing.
Further still, if all 3 pitots (A,B,C) aren't producing what they were (400kts) at X deployment, you can state that X is 'probably' correct and the other 3 pitots are iced, by looking at the trace back prior to the disagree and comparing it with X values.
If it then disagreed, you could retract it, clean it, redeploy it, and check again.
It can't be worse than blighting a cockpit with 3 disagreeing forms of information with no way to recover from it, can it?