Incorrect airspeed

While flying i’ve noticed that the autopilot it responding to lower airspeeds than it should. The speed was set to mach .87 and remained at .85. After decreasing the speed it also decreased, again it decreased to .83. Is there any solution to why this could be happening? Even at lower altitudes there is a 10kt trend in airspeed.


I’ve been having the same issue on some flights, but not all. To get to M .86, I have to set my autopilot to M .89

Which aircraft were you in?

It was doing it earlier in the 717-200. Currently in the A380 tracking from Abu Dahbi to Los Angeles

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What was your VS at the time? And is it for the whole flight?

Right now its at 0 and still doing the same thing, but I was climbing at about +2500fpm.

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Okay and is it happening for the entire flight. Also are you heavy?

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Yes, need quite a lot of fuel for the long flight i’m currently doing.

What’s your cruise alt that you immediately climbed to?

31,000FT, and then will step climb later on for efficiency.

I was thinking the issue is because you didn’t step climb… if you are climbing up to around flight level 300 then there should be no issues as long as you wait an hour or so before reaching your final cruise alt. Not sure what the issue is then, my apologies.

I would suggest a VS of 2000 though when you are heavy just to ease the aircraft and to stop the aircraft losing too much speed.

This is a known issue on some of the aircraft.


Managed the climb at only about 89%, but thanks for the advice everyone!