Flying below 550GS on 787-9 and still getting the "overspeed" alarm thing

as the title says :)

But, what is your air speed? Ground speed has nothing to do with overspeeding…it’s all about your air speed.


I agree, the mechanics between GS/AS and other factors like windspeed and altitude can severely seperate the two.

The higher you climb the more the airspeed indicator comes down so if you are cruising at 349 knots airspeed do expect to overspeed horn to sound. Same deal when climbing into the Mach speed which starts at FL280 if you cruise to close to it then as it slowly comes down and your airspeed hasn’t changed then same as before the overspeed horn will sound.

If you’re cruising at 550GS, you’re going wayyyy too fast and probably were around 335-349 KIAS.

787-9 goes at around 310-320 for KIAS to normal cruise

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I’m going M 0.86 (253KIAS) at FL380, I see the red line appear at 270KIAS on my HUD which is when I start to overspeed.

Yep, don’t go any faster than that. 787 usually cruises at M0.85 anyway.

550 GS is actually not unusual at all, especially when you’re at cruise, at Mach 0.85, with a tailwind. Definitely not way over speed at all.

You can fly the 789 up to Mach 0.9 without issues. Just don’t pass the red bars on the air speed indicator. Simple as that.


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