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EGPWS(Enhanced Ground Proximity Warning Systems) or TAWS (Terrain Avoidance and Warning System) systems create terrain and obstacle alerts both visual and aural. But in some configurations they can be manually inhibited to prevent nuisance alerts. My question is are these alerts created by TAWS are being stored in the flight recorder even when they are manually inhibited?

Anyone got any tips about where should I ask this question other than here?

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    $\begingroup$ I think it really depends on the specific implementation of the aircraft/EGPWS computer. $\endgroup$
    – ocirocir
    Oct 16, 2023 at 14:57

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It’s a question of timing. If the pilot inhibits a TAWS mode before an alert condition exists, the TAWS will not issue an alert. If no alert is issued, the FDR can’t record it as it was never issued. The FDR can only record events that show up on the data bus. The fact that the pilot did inhibit the alert mode is recorded by the FDR.

Despite the lack of a TAWS alert when inhibited, the specific data that is used by the TAWS to determine if an alert should be issued would still be sent from the other systems and that data would be recorded by the FDR.

If the pilot inhibits an alert after it is active, the FDR will record the alert and the subsequent inhibit/cancellation of alert.

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This depends heavily on what aircraft it is and how the specific systems have been programmed. I'm not a pilot but I think that it would still be able to detect the alerts because all the other data that is being fed into the alert system is still being monitored, so it's easy to know whether the alert would have been triggered.

I've seen air crash investigations where they are able to see that a pilot had inhibited an alert and then they use the data that is collected alongside to determine whether any alert would have been there.

In most aircraft, the inhibit switch is a physical switch that is not emulated, this would mean that the power to the system would be cut. In that case, one could only predict whether the system would have been triggered.

The best document about this that I've found till now is this https://www.bahamas.gov.bs/wps/wcm/connect/0cf4b5c7-d099-4320-b839-ef5e33c8e58a/AC+07-002+Flight+Recorders+%5BA%7D2011.pdf?MOD=AJPERES

I didn't read the entire document but I hope it's of help.

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  • $\begingroup$ If that document answers this question, it would be great to summarize the relevant parts in the answer itself. Links can serve as complimentary info, but shouldn't be the main meat of the answer. $\endgroup$
    – Jamiec
    Nov 21, 2023 at 13:44
  • $\begingroup$ @Jamiec the link does not entirely answer the question. It provides a bit more insight to where I got my conclusion (above link) from. $\endgroup$ Nov 21, 2023 at 13:50
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    $\begingroup$ Thats fine, quote the relevant section that gave you that conclusion $\endgroup$
    – Jamiec
    Nov 21, 2023 at 16:18

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