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Old 20th Mar 2019, 20:15
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wiedehopf
 
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Originally Posted by yanrair
Another scenario is that one airspeed is faulty, but the other two work - there are three airspeed indicators. That one is easy since you go for the two that agree. Backed up with GPS.
And in all these cases GPS will still work.
So the changes of losing AoA information AND Airspeed information at the same time are pretty remote.
This is just for information since there seems to be a misunderstanding about the functions of the various systems here.
Airspeed has little to do with GPS (ground speed). It is something you can look at if you approximately know the winds of course but calling it a backup?
(And at 7000 ft you also have to take air density into account, which makes ground speed even harder to use)

As has been stated before, the airspeed and altitude are corrected for AoA.

That is because the static ports and pitot probes are affected by the airflow around the airframe.
At different angles of attack that flow is different, thus there is a relatively small correction made.

Just have a look at the differing airspeed/altitude introduced by the AoA misreading in the Lion Air report FDR graphs:
https://www.flightradar24.com/blog/w...ary-Report.pdf

Last edited by wiedehopf; 20th Mar 2019 at 20:35.
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