Welcome Guest. Sign in or Signup

3 Answers

Altimeter (non-pilot question)

Asked by: 6262 views General Aviation

Isn't it true that altimeters measure height above sea level?  Is this because there is no accuarate way, without some type of radar, to measure height above ground?

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.

3 Answers



  1. Koehn on Dec 29, 2010

    It’s true that pilots don’t have a good way of determining altitude Above Ground Level (AGL) in most aircraft; but knowing your AGL isn’t always helpful.
    Imagine you’re flying along contentedly (thanks to your radar altimeter) knowing that you’re 3000′ AGL. Ahead of you are some mountains: are you high enough to clear them? Well, the chart won’t tell you their altitude relative to your altitude; the only meaningful way to chart their altitude is by measuring it relative to Mean Sea Level (MSL). So you as a pilot need to know your own altitude relative to Mean Sea Level. Hence the pressure altimeter.
    Another scenario: you’re landing at an airport, but you can’t see it because of low clouds. You know that you’re currently 500′ AGL, but at what altitude is the runway? Again, you need a common reference for measuring altitude, and that reference is MSL.

    +2 Votes Thumb up 2 Votes Thumb down 0 Votes



  2. Keith on Dec 30, 2010

    Koehn is right, it’s essential to have a common reference. It can also be good though to know your height above the ground. Flying the <a href=http://www.howitflies.com/Douglas-A-4-Skyhawk”>A-4 Skyhawk</a> during Navy training we learned to make good use of a Radar Altimeter (radalt). Besides being good for low level navigation you can use it in instrument work by setting an alarm for decision heights, etc.

    0 Votes Thumb up 0 Votes Thumb down 0 Votes



  3. Earl Kessler on Jan 17, 2011

    We also use MSL with current altimeter setting so that we can maintain accurate separation from other traffic.  If ATC assigns an altitude to IFR pilots, and you are flying VFR, you may only be separated by 500 ft from closing IFR traffic.  It is essential that you be on your assigned altitude to ensure safe separation.  Keeping your altimeter set to local AWOS, ATIS, ASOS or ATC-given altitudes keeps this safety factor.  Don’t be shy to ask ATC for a current altimeter setting if it’s been a few minutes since your last adjustment.

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes


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.