Quote:
Originally Posted by
overthewing 
This is doubtless a dumb set of questions; if so, I apologise.
If you're flying the plane, and all the computers suddenly throw in the towel, is there any way of knowing what altitude you're at?
If you suspect that the problem is iced-up pitots, would descending to a lower altitude in order to unblock the tubes be sensible, or not?
Is there any way to know that you're a lot closer to the ocean than you'd like to be?
I sense that you are suggesting they possibly descended to find warm air to melt the frozen pitot tubes and then possibly impacted the ocean because they didn't know their altitude.
1) Descending to warm air would mean a huge fuel penalty. They only have enough fuel to reach their destination at cruising altitudes. Descending even for a short time would mean they would not have enough fuel to complete the flight.
2) The standby altimeter relies on barometric pressure only and will continue to give accurate readings even with total electric or computer failure.
Lost,
I'm very sorry but I have to disagree:
ETOPS flight planing has legal requirements for fuel reserves in case of In-flight Engine Shut Down, plus, de-pressurization (one or two engines running) to reach ETOPS suitable alternate aerodromes. In warm air (equatorial area) one reaches positive TAT readouts between 20 to 15000, and I'm sure a very positive TAT at about 10000'. In the event a pilot decides to descent for safety reasons, there is no pressure to continue to destination. Commercial interests, always come
after safety. He may latter decide to climb again, but the decision process to resolve a failure is far more important than to comply with time-tables.
Flyinheavy:
As far as I have seen the ISIS has the Altimeter included, so not so sure about Stby Altm.
I tend to agree with you. And in my very humble opinion, without IR's and a faulty ISIS, they would not have the slightest chance to keep control of the aircraft.