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Most modern airplanes have some sort of crew alerting system. These alerts are generally conveyed through display messages, lights, and aural alerts. Aural alerts can either be tones or voices. For example, on many Boeing airplanes, most caution alerts are indicated by a beeper and most warning alerts are indicated by a siren. However, on most McDonnell Douglas airplanes, most alerts are indicated by a voice, such as in, "engine one fire," "landing gear," and "stabilizer motion." Most airplanes will have a mix of both, but generally "stick" to one form of aural alerts over the other. For example, most Airbus airplanes have tone aural alerts, but some specific conditions, such as a stall, will trigger a voice aural alert. Overall, which is better? Can voice alerts be more distracting, or are tones not specific enough to orient the crew to an abnormal condition?

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  • $\begingroup$ In episode 94, Jamie Hyneman thought the simulator was saying, Warning. Don't Think. ... It was saying, Don't Sink. - He grew up in Michigan and has a degree in Russian linguistics, and not even he could understand the thing. $\endgroup$
    – Mazura
    Oct 2, 2022 at 23:26

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Older aircraft designed before the B787 typically had the variability in design that you refer to. When the B787 started development, the FAA issued special conditions that required Boeing to address issues the FAA had with the alerting.

The FAA was concerned about proper prioritization of alerts and reducing ambiguity. Eventually, the Special Conditions resulted in a revision to the regulations, § 25.1322. That was followed with a new Advisory Circular AC 25.1322-1 - Flightcrew Alerting.

Generally, voice alerts are where a specific response is required immediately, think TAWS or TCAS. The issue with voice alerts is that they can not overlap. Distinct audio alerts can exist simultaneously - e.g., overspeed with a "pull-up" ground proximity alert.

I suggest a read through of the AC to get a better understanding of the current design guidelines.

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  • $\begingroup$ "The issue with voice alerts is that they can not overlap." But you can easily time interleave them. “BANK ANGLE, BANK ANGLE; PRESSURE, PRESSURE; BANK ANGLE, BANK ANGLE; PRESSURE, PRESSURE”. Learning what the different sounds mean is already difficult enough, if you have to learn all combinations of them it’s almost impossible. $\endgroup$
    – Michael
    Oct 2, 2022 at 15:48
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    $\begingroup$ @Michael As someone who spent 25 years developing avionics, I can say it is definitely not 'easy to interleave' the messages. Every alert is assigned a priority in the system. TAWS, Windshear, and TCAS have different responses and thus the voice alerts to identify the action to be taken. Once an alert starts it must finish (though not necessarily repeat). A higher priority alert can follow, but the lower alert won't resume until the higher priority is no longer present. The FAA is very concerned with misleading alerts caused by alerts run together. So allowable combinations are very limited. $\endgroup$
    – Gerry
    Oct 2, 2022 at 19:43
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This is only my personal experience from my initial-course CRJ simulator training, but I found that voice alerts tended to be more effective at distracting you or pulling you out of mental fog.

For example, with the Rockwell Collins Pro-line avionics suite, the tones and voice calls are distinctive to that system. The landing gear warning horn is a dual frequency continuous tone that (to me at least) sounds exactly like the old TV test pattern sound from the days of broadcast TV, when they shut down at 2AM each night.

I found that if pushed to the edge of mental saturation by abnormal and emergency tasks, (usually while nearing burnout late in a 4 hour session - instructors can be evil), if that tone came on during an extreme workload situation it would be very easy for it to just become part of the background noise if it wasn't noticed right away, whereas the "TOO LOW, GEAR, TOO LOW, GEAR" voice alert from the Ground Proximity Warning System, that would come on when you got lower, had a much better effect at bringing you out of the fog.

So if I had to choose one or the other, from an effectiveness perspective I'd go with voice alert, but there are limitations there as well.

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