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Guest fyrestrtr

Strange Engine Behavior

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Recently on a flight I got into some really strong tail winds (102 Kts), however on the jet that I was flying (a PMDG 747) the throttle was still going at about 94% N1.Is this normal? Shouldn't the throttle be idled back a bit due to the strong tail winds? I had the economy settings at 50 -- which is about average and the plane wasn't really pushing the limits of its engines, so I thought a tail wind would help with fuel and the total time.Just curious as to the behavior. Still managed to land with plenty of reserves.

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The aircraft (autopilot and autothrottle) doesn't know anything about the tailwind. It's flying within a mass of air, and is simply trying to maintain the correct AIR speed relative to that air mass. Therefore, the throttle will not change. If the air mass just happens to be moving at 102 knots in the right direction, your ground speed will be increased. This will get you to your destination sooner and more economically.Regards,JerryH

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as jeff says, aircraft don't care about groundspeed. the relative airspeed as all the matters -- IAS (indicated airspeed).the direction and strength of the jetstream really changes flight times. most US flights west to east have a shorter 'gate to gate' times as the planes fly faster going with the jetstream (west to east), not that the pilots set a higher IAS.all of this leads to a discussion of relative motion ... why FS is such a great video game as it can teach all about physics and math (to name a few of the important sciences).--

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Oh I see what you mean. The aircraft's systems only care about the speed in the air mass, not the ground. So if I'm caught in some strong headwind, then the aircraft will have a slower ground speed, but the same airspeed, since the autopilot only has to maintain the IAS.You know, I always knew it was Indicated air speed, only now it really hits what it actually means in terms of real flight.

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You may also experience the auto-throttle advancing or retarding power if you encounter windshear. All it's trying to do is maintain the IAS/Mach that you set it for.John M

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