max cruising speed 0.86 but I am travelling at 0.92!!!

RC Next Gen AM Guest


I am in my boeing 747-400 at 36,500ft. I was concerned at how slow I was taking to get to destinations. I recently done flights from London Heathrow (EGLL) to KJFK and KEWR and they took nearly 8hrs. In real life they take only 6 1/2 ish. So at my cruising altitude I cranked the auto throttle up to 320 with the speed button illuminated. When I toggled this to the Mach button it said 0.92 and I thought the max cruising speed of this aircraft is mach 0.86?? Is this ok. or if it were real life would my aircraft be in a million pieces in the atlantic?? If it is ok, what would you expect the maximum speed setting to be, i.e. 350, 400? Also, the overspeed warning did not come on so I assumed it was ok?

Also, I don't know if its unrelated, but on my garmin gps, my eta and ete get slower as the flight goes along. I actually timed it, every 30mins my eta gets pushed back by 8mins and I can't understand why given the aircraft starts to get a bit quicker as we burn off fuel??? Does anyone have any ideas why this is? Have a got a setting on the game wrong??

thanks in advance for your help!!


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First off I'm not an expert at this and hopefully someone else will give a more detailed explanation. I think that there is nothing wrong with the mach box displaying 0.92. When you're flying at 36500ft the air is a lot thinner and colder and therefore the plane will be travelling a lot faster than indicated. This doesn't mean that your plane is going to blow up into millions of pieces. What I normally do is programme my speed into the autothrottle with the speed button. When I reach 20000ft I change the auto throttle to my desired mach speed.
As I said, I'm not absolutely sure about this. If anyone knows better go ahead.
355 is the absolute max number that should be entered into the speed box.
Sorry but I'm not sure why your eta and ete are slowing.
Good Luck

Pro Member First Officer
leadfoot First Officer

I don't know about the eta problem, that is strange, but .92 mach is not unreasonable for the 747. I have cruised at .92 or better in the 747. The highly swept wing is the reason for the high cruise speed. I believe the wing is swept 37 degrees, about the same as the Cessna Citation 10.


Most aircraft are designed with a "safety zone" so to speak; i.e. max cruising speed is usually lower than the 'maximum' design speed. e.g. the A380 can withstand up to M 0.96.

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