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2 Answers

Airspeed indicator – MPH

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Aircraft Systems

Hello guys i have a doubt since a while ago, in some aircrafts the airspeed indicator shows knots and mph at the same time with a little difference, for example: Knots 60 and mph 67, what kind of miles does the mph refers? It is nautical miles per hour or statute miles per hour?

Thanks for your help.

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2 Answers



  1. John Scarry on Feb 18, 2021

    The airspeed indicator shows statute miles per hour—usually on the outer ring if there are both. The conversion factor for nautical miles to statute miles is 1.15 so 60*1.15 = 69 mph which is close.

    This image https://www.touringmachine.com/images/AirspeedBlackBG200.jpg shows both and if you look at 140 kts on the inside ring it matches pretty well with 161 mph on the outside ring. Same with 60 and 69 though it’s a little harder to see.

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  2. KDS on Feb 18, 2021

    The miles in the MPH are statute miles, the same as what a common American car speedometer measures. 5,280 feet.

    To do the mental gymnastics from one to the other, multiply MPH by 0.87 to get Knots or multiply Knots by 1.15 to get MPH.

    The FAA mandated the aircraft be certified in Knots starting somewhere in the 70’s as my foggy memory recalls.

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