Welcome Guest. Sign in or Signup

1 Answers

True Altitude vs Indicated Altitude

Asked by: 598 views ,

During my commercial training I am learning much more about how our Indicated Altitude can have errors due to non-standard atmospheric conditions.  We set our altimeter to nearest available setting which takes care of much of the variance between true altitude and indicated altitude.  But when we are flying along on our XC on a nonstandard day how do we make sure we are not going to bump into things up there? During my PPL training we talked very little about variances between true altitude and Indicated.   On my charts we would ensure that we were at least 500' above any obstacle along the way.  But is that really enough?   If we are 25C off of a standard day couldn't that 500' be reduced to 10'?  Also what about staying below/above airspaces?  Isnt ATC  going off of True Altitude?  Could I bust bravo or the SFRA(in the DC Area) due to these errors? 

Ace Any FAA Written Test!
Actual FAA Questions / Free Lifetime Updates
The best explanations in the business
Fast, efficient study.
Pass Your Checkride With Confidence!
FAA Practical Test prep that reflects actual checkrides.
Any checkride: Airplane, Helicopter, Glider, etc.
Written and maintained by actual pilot examiners and master CFIs.
The World's Most Trusted eLogbook
Be Organized, Current, Professional, and Safe.
Highly customizable - for student pilots through pros.
Free Transition Service for users of other eLogs.
Our sincere thanks to pilots such as yourself who support AskACFI while helping themselves by using the awesome PC, Mac, iPhone/iPad, and Android aviation apps of our sponsors.

1 Answers

  1. John D Collins on Jul 13, 2017

    Yes there can be a significant difference between true altitude and MSL. MSL is the pressure altitude (29.92) corrected for the local barometric setting. Your transponder and any ADS-B system sends your uncorrected pressure altitude to ATC where the computer corrects it to show the controller your MSL altitude. So ATC will see the same value you have on your altimeter if it has the pressure set to the local value. True altitude is important if you don’t want to collide with the terrain or an obstacle, but if you don’t want to collide with another airplane or get in trouble with ATC, you will use the MSL altitude indicated on your altimeter. If you have a GPS altitude, it will indicate closer to true altitude as it is not affected by temperature.

    0 Votes Thumb up 0 Votes Thumb down 0 Votes

The following terms have been auto-detected the question above and any answers or discussion provided. Click on a term to see its definition from the Dauntless Aviation JargonBuster Glossary.

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.