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pdungan

747 airspeed

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I was flying a 747 and doing 250 knots below 10,000ft- then 340 knots up to approx 25,000/30,000ft- then approx mach 0.84 at approx 30,000ft and above but my airspeed only indicates around 280/290 knots how is this? I taught my indicated airspeed would be higher than this.

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That indicated airspeed is correct.  In cruise focus on the mach number, TAS & Ground speed.

 

To put it in very basic terms, the higher you climb the less dense the air becomes.  So less dense air impacting the static port.

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As flex stated, focus on mach. mach change over happens around 28 to 29 thousand. I fly around at FL400/FL410 and the indicated airspeed is about 258 kts. Most modern planes will automatically switch to mach when climbing through mach change over altitude.

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