Mon Feb 13, 2017 4:45 pm #1519052
kanga wrote:.. and it relies on external signals and internal power, either of which could fail at any time. If barometric altimeter is working at start of flight, set to whatever subscale value pilot chooses to use, there is a pretty good chance it will keep working adequately throughout any sort of flight which I would undertake.
External signals are beyond improbably to fail. GPS is now too necessary that the US will never turn it off. Maybe.
Is the likelihood of people getting their altimeter settings mixed up, or their maths wrong higher or lower than power failing these days? Given that many people (most?) fly with a battery powered navigation device as well as an aircraft power source, I very much doubt that the loss of both will occur with any regularity.
Modern civil airliners have to have an emergency electrical system available for 10^-9 of the flying time. 1 failure every thousand million hours (I think!).