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For example, has an Airbus gone from cruise flight into an automated unrecoverable nose dive until it hit the ground because an AOA sensor failed in flight?

Moreso, are there any cases of an AOA sensor failing on an Airbus, and the plane not crashing?

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  • $\begingroup$ Air France 447 (though outcome was much due to pilot error)? $\endgroup$ – BillDOe Dec 21 '18 at 22:34
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    $\begingroup$ 447 was because the pilots became focused on wild and crazy airspeed indications and failed to go back to their basic IFR skills of flying pitch attitude and altitude when the speed indications don't make sense, and eventually becoming mentally saturated, confused, and settling into a mental "tunnel vision" state. The right seater was in total panic mode and had the side stick at the aft limit almost all the way down, and the left seater didn't think to override him. $\endgroup$ – John K Dec 21 '18 at 22:54
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    $\begingroup$ IIRC the basic cause was thought to be airspeed fluctuations caused by ice crystal accumulation in the pitot probes. The crystals build up at the first bend in the pipe, away from the heated portion which is only near the tip. Bizarre how that particular phenomenon only started to show up in incidents over the last 10 or 15 years or so. Everybody provides pitch and power tables for crews to fly with unreliable airspeed indications nowadays. $\endgroup$ – John K Dec 21 '18 at 23:04
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    $\begingroup$ Related: en.wikipedia.org/wiki/XL_Airways_Germany_Flight_888T $\endgroup$ – Thomas Dec 22 '18 at 6:37
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    $\begingroup$ You are making an assumption about the cause of the accident of JT610. There is not a final report, yet. While your assumption is a probable cause, it’s not yet confirmed as being the sole cause, or a contributing cause. $\endgroup$ – Penguin Dec 22 '18 at 10:10
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if a single angle of attack sensor fails

No.

An A320 has three AoA sensors. If one reports a different value to the other two, the avionics will ignore values from that AoA sensor and use the values from the other two.


If two of the three fail and report consistent values - the avionics will believe the third is the odd-one out and unreliable.

If those two both both report a consistent and overly high AoA then the flight protections will apply a nose-down input in an attempt to restore the AoA to normal values and prevent a stall. this input is averaged with the pilot's inputs.

As I understand it all the following conditions must be met for the AoA protections to be erroneously invoked and cause a nose-down input:

  • Two AoA sensors fail and
  • Both report the same value and
  • The value is one that would cause a stall if true.

According to Airbus' Safety-First magazine:

In normal law, on a protected aircraft, exceeding the AOA value of the α PROT threshold would immediately trigger the high AOA protection, thus resulting in a nose down pitch rate ordered by the flight control laws. Further increasing the AOA by maintaining full back stick would eventually result in reaching the α MAX threshold.


are there any cases of an AOA sensor failing on an Airbus, and the plane not crashing?

I expect there are many.

There are even cases of two AoA sensors simultaneously failing and the aircraft continuing, after some control problems.

For example this incident reported by Aviation Week

German investigators studying the cause of an uncommanded pitch-down of a Lufthansa Airbus A321-200 near Pamplona, Spain, in November 2014, hope to discover the probability of similar events linked to frozen angle-of-attack (AOA) sensors as the investigation continues. In the interim, both the European Aviation Safety Agency (EASA) and Airbus have published directives alerting pilots of the issue and the workarounds.

...

The captain continued to hold “more than 50%” rearward stick in stable flight for a period, but with help from technicians on the ground, the crew was able to reconfigure the automation into the aircraft’s alternate control law, rather than its normal “direct” law. The action removed the alpha-protection checks and canceled the nose-down input. The aircraft then continued to its destination.

...

Airbus in early December issued a Flight Operations Transmission and Operations Engineering Bulletin to all A320-family aircraft operators noting that “if two or three AOA probes are blocked at the same angle, an increase of the Mach number may activate high-angle-of-attack protection,” which results in “continuous nose-down pitch rate that may not be stopped with backward sidestick inputs, even in the full backward position.” The recommended fix is to turn off two of the three ADRs, which puts the aircraft in alternative control law, deactivating the high AOA protection.

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  • $\begingroup$ Great answer. Thank you! $\endgroup$ – Willy A Dec 22 '18 at 1:11

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