In a case such as United 326 - where an aircraft got cleared for takeoff while other planes at the same time get cleared to cross that runway - how would an outside party that picks up on the mistake inform the others that a disaster is about to happen and that people need to take immediate action?

Would they call mayday, or just shout out in "freeform", something along the lines of "Imminent collision, runway 19C!".

  • $\begingroup$ "Hey tower, did you mean to clear United 236 while clearing the crossing for Oceanic 123?" $\endgroup$ – Ron Beyer Sep 27 '18 at 18:39
  • $\begingroup$ @RonBeyer I meant in a case where things are seconds away from going disastrous, where people need to act immediately or there will much sadness. $\endgroup$ – MichaelK Sep 27 '18 at 18:56
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    $\begingroup$ If we're talking literally seconds, then keep in mind that the pilots involved will need to (1) realize that you're talking about them, or to them; (2) determine the action required by them to resolve the situation; (3) execute that action; and (4) have the action take effect. That's a mouthful, especially since even your brief transmission would take at least some 2-3 seconds to rattle off (at the standard rate of about 100 words per minute, and assuming you say "19C" as "nineteen center"; not that "nineteen see" or "one nine see" would save you much time...). $\endgroup$ – user Sep 27 '18 at 19:03
  • $\begingroup$ @MichaelK Usually seconds doesn't mean enough time to get a large airliner out of the way. A loaded 737 can weigh more than 70 metric tons and engines don't react as quickly as they do in the movies. Even if you started screaming "STOP STOP STOP" into the radio (which will get everybodies attention), a few seconds will just mean more time for the pilots to realize how bad this is going to be. An airliner goes from "cleared for take-off" to the end of the runway in less than 30-45 seconds. $\endgroup$ – Ron Beyer Sep 27 '18 at 20:48
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    $\begingroup$ @Zeus If it's really as important as OP indicates, I wouldn't bother waiting to cut in; just transmit. A continuous "STOP STOP STOP STOP STOP STOP" similar to what Ron Beyer suggests doesn't need much time in between other transmissions to get through intelligibly. The harder part is for the person at the receiving end to identify who needs to stop -- does this apply to them? Braking hard is going to give the passengers a bit of a jolt; I dare say no pilot wants to give their passengers a rough ride. $\endgroup$ – user Sep 28 '18 at 7:54

To quote an answer by kevin on another question from last year:

What's the procedure? The procedure is, be creative to save as many lives as possible!

Really. The procedure is to determine a course of action which will likely result in the best outcome for everyone, utilizing all resources and given all constraints. Period. It is as simple as that.

There are infinitely many scenarios, and one cannot be trained for everything.

If you need to communicate something as quickly as possible in order to avoid a disaster, and calling "mayday, mayday, mayday" will be a significant waste of valuable time, then the answer is clear: don't call mayday. Just say what you need to say.

If you know what the other aircraft need to do in order to avoid a collision, perhaps it would be a good idea to announce "Go around, go around, go around!", "Cancel takeoff, cancel takeoff, cancel takeoff!", or "Hold short, hold short, hold short!", as appropriate.

In the case of Air Canada 759, where an arriving airliner mistakenly lined up to land on an occupied taxiway instead of the runway, a pilot on the taxiway announced: "Where's this guy going? He's on the taxiway." This probably wasn't the best possible thing to say, but the airliner went around and avoided a collision.

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    $\begingroup$ I feel honored to be quoted (-: $\endgroup$ – kevin Sep 28 '18 at 1:43
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    $\begingroup$ So in brief you are saying: cut in, get the message across, procedures matter less than saving lives. $\endgroup$ – MichaelK Sep 28 '18 at 7:32

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