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A non-answer on this question claimed that:

the idea that maneuvering with the stall warning activated will somehow damage us, causing us to ignore its warning when the chips are down and AOA is up, is just silly

which sounds wrong to me, as I vaguely remember reading about crews becoming accustomed to frequent warnings, spurious or real, and disregarding them when they became critical.

Which, if any, aviation accidents or incidents have had among their direct or contributing causes a crew that ignored a warning due to being used to it being spurious or unimportant?

I am looking for substantiated answers only, remember that this site is not a venue to speculate on aviation accidents.

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  • $\begingroup$ I recall an episode of aircrash investigations where the crew pulled the fuse on a nuisance warning during taxi, which then had consequences during flight. Though I don't quite recall which flight that was and my google-fu is failing me on it. $\endgroup$
    – ratchet freak
    Commented Aug 7, 2019 at 9:32
  • $\begingroup$ @ratchetfreak I think I've read that report, but can't recall the details; I'll give it a try. $\endgroup$
    – AEhere supports Monica
    Commented Aug 7, 2019 at 10:58
  • $\begingroup$ The pilots on LAPA 3142 ignored the configuration warning, but I don't remember why. $\endgroup$
    – TomMcW
    Commented Aug 7, 2019 at 16:18
  • $\begingroup$ @TomMcW afaik, due to an ongoing personal discussion. The report is quite dry and does not provide details, but there doesn't seem to be any indication of them being used to it. $\endgroup$
    – AEhere supports Monica
    Commented Aug 9, 2019 at 12:23
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    $\begingroup$ Gradual accustomisation to abnormal situations which causes an incident is called 'normalisation of the deviance'. There is a very nice write-up by Tim Davies, a former RAF instructor, where he explains it very well. It is not about warnings in this case, but nevertheless a good read. $\endgroup$
    – DeltaLima ♦
    Commented Aug 13, 2019 at 11:47

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Just last year the crash of an Air Niugini flight was directly related to pilots ignoring warnings

The captain and first officer ignored a total of 17 audible warnings that they were flying too low.

“The crew seemed to have disregarded and talked over all the caution annunciations. The crew had experienced those type of cautions on previous flights and perceived them as nuisance alerts with no resultant consequence.”

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    $\begingroup$ I decided to give this answer the tick because it is, in my opinion, the most clear-cut example of accustomization from among the answers provided. $\endgroup$
    – AEhere supports Monica
    Commented Oct 3, 2019 at 11:25
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A notable accident was the Helios Airways Flight 522 crash, where the pressurization system was turned off and the pilots ignored the warning horn because they thought it was the takeoff config warning. From the Wikipedia page:

As the aircraft climbed, the pressure inside the cabin gradually decreased. As it passed through an altitude of 12,040 feet (3,670 m), the cabin altitude warning horn sounded. The warning should have prompted the crew to stop climbing, but it was misidentified by the crew as a take-off configuration warning, which signals that the aircraft is not ready for take-off, and can only sound on the ground.

The official accident report explains the source of the confusion in more detail (emphasis mine):

The Board examined the flight crew’s actions to disengage the autopilot and auto-throttle, and to retard the throttles upon onset of the warning horn. Given that the expected reaction to a cabin altitude warning horn would have been to stop the climb (there was no evidence to this effect), the Board considered such actions to signify that the flight crew reacted to the warning horn as if it had been a Takeoff Configuration Warning (the two failures use the same warning horn sound). [...]

The warning horn was designed to signal two distinctly different situations. The Board considered the role of experience in interpreting and reacting to the warning horn. In the course of his career, a pilot is generally likely to only hear the warning horn when it is associated with a takeoff and a takeoff configuration problem. [...]

Most pilots are not very likely to experience a cabin pressurization problem and the associated warning horn at any time during their line flying.

Conclusion: Never use the same warning for multiple situations, if the pilots will only get used to one of them, otherwiese they will ignore the warning for the other situtations!

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  • $\begingroup$ This isn't the same thing as the OP is asking. It wasn't a case of becoming accustomed to an alarm, it was misidentification of the alarm. $\endgroup$
    – TomMcW
    Commented Aug 6, 2019 at 19:00
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    $\begingroup$ @TomMcW Yes, but they misidentified it because they became accustomed to it. $\endgroup$
    – Bianfable
    Commented Aug 6, 2019 at 19:30
  • $\begingroup$ @TomMcW I thought the same when I read the first draft, but with the extra information about the two alarms using the same horn, I think it does count. $\endgroup$
    – AEhere supports Monica
    Commented Aug 7, 2019 at 6:46
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A Valan Air Cargo An-26 crashed in Cote de Ivoire on the 14th of October, 2017, while performing a charter flight. The aircraft descended below minimums on approach and impacted terrain, in this case a water body, short of the runway.

Among the contributing factors, the BEA listed "De-activation of EGPWS audible warnings due to nuisance alerts".

The following is taken from the translation of the report provided by AVHerald, so I cannot confirm its accuracy; the original report can be found here if any French speakers want to double check. Emphasis mine:

The BEA reported the EGPWS was found fully and properly working, however, even on the previous flights the EGPWS had been sounding premature terrain warnings obviously related to an incorrect altitude reported by the Air Data Computer. A difference of about 700 feet between altitudes reported by ADC and radio altimeter was recorded. While the GPS data appeared correct and agree with the radio altimeter, the ADC data transmitted via ARINC 204 bus appeared incorrect.

The BEA annotated: "The regular presence of untimely (premature) Alerts from the EGPWS may have encouraged the crew to ignore these alerts, probably going so far as to disable them."

Also:

The EGPWS nuisance alerts were confirmed to have been present for a number of flights, however, had never been reported to the company. Therefore no action to identify and correct the malfunction were undertaken. A reliable Terrain Warning would certainly have made the crew aware of the vertical profile and correct their flight path to climb.

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  • $\begingroup$ I don't think that "deactivation due to nuisance alerts" should count. There were plenty of such cases, but this is something almost opposite: disable the warning so that you don't get accustomed to it. (A particularly nasty example when the crew disabled the gear together with the warning). $\endgroup$
    – Zeus
    Commented Aug 14, 2019 at 2:01
  • $\begingroup$ PA-44 has a gear warning whenever you pull throttles back; as a result, you may be descending for qute some time hearing these beeps. There is a mute button, but the instructor never used it when I flew the airplane, exactly so that we don't forget. But instead, I did feel that I just started to ignore it... $\endgroup$
    – Zeus
    Commented Aug 14, 2019 at 2:04
  • $\begingroup$ @Zeus I partially agree, except for two points: first, that the alerts were an ongoing issue during previous flights and went unreported, normalizing the entire situation, and second, that it is unclear to me from the AVHerald translation whether it was conclusively established that the alert was muted: "The regular presence of untimely (premature) Alerts from the EGPWS may have encouraged the crew to ignore these alerts, probably going so far as to disable them". I'll ask in the Hangar whether a French speaker could go through the report. $\endgroup$
    – AEhere supports Monica
    Commented Aug 14, 2019 at 14:27
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On May 9th, 2012, a Sukhoi Sukhoi Superjet 100-95 on a demonstration flight in Indonesia crashed into a mountain while in clouds. The Terrain Awareness and Warning System (TAWS) gave warnings, and the crew could have still avoided the terrain up to 24 seconds after the first warning, but they ignored and then inhibited the warnings, commenting that it must be a database issue. The crew had believed in their brief that there was no high terrain nearby and then became disoriented.

On April 10th, 2010, a Polish Air Force Tu-154 crashed during landing. As they were landing at a military field, it was not in the TAWS database. This meant that the system did not recognize that they were trying to land and started giving alerts. Rather than using proper procedure and engaging the "terrain inhibit" function, the crew changed the captain's altimeter setting, telling the system it was higher than it actually was. They later ignored multiple TAWS warnings and did not follow proper go-around procedures until it was too late.

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