When the crew receives "airspeed disagree" message on the primary flight displays, they may face some hazardous situation. Is there any procedure, using a table containing pitch, power, altitude and weight, to avoid stall, for example?

  • 4
    $\begingroup$ This has the exact same answer as your other question about altimeters, so you may just want to ask one about "unreliable flight instruments" instead of one for each of the different instruments... $\endgroup$
    – Lnafziger
    Commented Jan 28, 2016 at 16:50
  • 1
    $\begingroup$ TURN ON THE PITOT HEAT! $\endgroup$
    – rbp
    Commented Jan 29, 2016 at 16:07

1 Answer 1


As you probably know this is the situation that occurred for AF-447 (Rio-Paris) on June 2009. From the BEA report:

The accident resulted from the following succession of events:

  • Temporary inconsistency between the measured airspeeds, likely following the obstruction of the Pitot probes by ice crystals that led in particular to autopilot disconnection and a reconfiguration to alternate law, [...]
  • The crew not making the connection between the loss of indicated airspeeds and the appropriate procedure,

This mistake happened previously. From the same report:

Four crews did not identify the unreliable airspeed situation: in two cases, the crews concluded that there was an inconsistency between the angles of attack; in the two other cases, the crew considered that the speeds were erroneous rather than unreliable.

Then the procedure that should be used in case of unreliable airspeed:

The philosophy for processing the anomaly is described in the “UNRELIABLE AIRSPEED INDICATION / ADR CHECK PROCEDURE” that is in Flight Manual (AFM) and transcribed in the Airbus FCOM and the Air France Operations Manual.

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This procedure which is to be known without the support of the documentation gives time to retrieve data from the documentation (this is what you wanted to know):

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See also:

  • 1
    $\begingroup$ What does "THRUST RED ALT" mean? $\endgroup$
    – Ben
    Commented Jan 28, 2016 at 20:56
  • 2
    $\begingroup$ @Ben: Thrust reduction altitude. The altitude at which the pilot reduces thrust after take-off. $\endgroup$
    – mins
    Commented Jan 28, 2016 at 21:08
  • 1
    $\begingroup$ Makes perfect sense to me now, thanks $\endgroup$
    – Ben
    Commented Jan 28, 2016 at 21:28

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