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2 Answers

Baro setting on altimeter

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General Aviation

My plane is set on autopilot and I receive an updated altimeter setting.  I reset the aircraft altimeter, but fail to reset the baro setting on the autopilot.  What would happen?

Would the autopilot be following the wrong pressure level causing my aircraft to be higher or lower that what’s being displayed on the altimeter?  

 

 

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2 Answers



  1. John D. Collins on Feb 11, 2011

    It is a good question, but the answer is dependant on which autopilot.  Many autopilots do not have a Baro input and hold the altitude based on the pressure at the time it was engaged.  Autopilots such as the Garmin GFC700 and the Bendix King KFC225 will automatically follow the changes made in the baro setting for the altimeter. If your autopilot doesn’t adjust the altitude when the barometer changes on the altimeter, then you have to make the change manually and reestablish the altitude that the autopilot is holding.

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  2. Kent Shook on Feb 12, 2011

    Student Pilot,
     
    If you’re flying an airplane with an autopilot such as the KAP 140 that has a Baro setting that’s separate from the altimeter setting, and you don’t change the Baro setting on the autopilot, the autopilot will be flying at the wrong altitude. However, as long as you did update the setting on the altimeter itself, it will still read correctly and you’ll be able to easily tell that you’re not quite at the right altitude.
     
    Usually, this is not an issue if you simply forget to do the reset in flight because you won’t be changing it much, and .01 on the altimeter roughly corresponds to a 10-foot change in altitude. However, if you forget to set the Baro setting on the autopilot prior to flight, it may be significantly different from the actual altimeter setting, and level you off somewhere other than where you’re expecting – So get in the habit right away of changing ALL of the altimeter settings, even if you’re not using the autopilot. Some airplanes (for example, a Cessna or Diamond Star that has a G1000 system but a King autopilot) have THREE places to change the setting: One on the G1000, one on the autopilot, and one on the backup altimeter. Make sure you know where your airplane needs that setting, and change every one of them every time.
     

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