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Altimeter reporting to ATC

Asked by: 2217 views ,
Aircraft Systems, General Aviation

On recent CC trip I filed for 7,000 and flew 7,000. ATC had no complaints but after the flight I looked at the flight profile on FlightAware. It reported 6,700. I was changing the altimeter for local pressure. So why was I reporting 300 foot lower than indicated?

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1 Answers



  1. John D Collins on Mar 24, 2019

    Your transponder replies with pressure altitude which is equivalent to what your altimeter would read if it were set to 29.92. Your altimeter indication is corrected by the altimeter setting, so is pressure altitude +/- baro setting to indicate MSL. Although your transponder replies with the pressure altitude, the ATC computer corrects it based on the current altimeter setting in your area, so the controller sees what you see indicated on your ship’s altimeter. My guess is that either FlightAware used your pressure altitude or did not have the current pressure setting for your area.

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