Welcome Guest. Sign in or Signup

1 Answers

Altimeter setting exceeding 31.00 in Hg and raising approach minimums

Asked by: 5240 views ,
FAA Regulations, Flight Instructor, General Aviation

. In the rare event that the local altimeter setting is over 31.00 in Hg, why is the decision made (by the FAA) to raise the minimums on instrument approaches if aircraft are operating in a region with this high of a setting? Assuming the typical kollsman window maxes out at 31.00 and the local altimeter is 31.05, you will still be flying at an altitude higher than whats indicated on your altimeter(assuming you have 31.00 set in your window). Therefore, regardless of what your approach mins are, you would still be above them, in this case approximately 50 feet. My logic may be wrong here, but I’ve just been having a tough time grasping the concept when the altimeter setting is above this 31.00 range. My only other thought would be that if the altimeter setting was greater than 31.00 in Hg, there is a chance that it could also be extremely cold and therefore the FAA is assuming worst case scenario and adding this buffer due to errors in the altimeter because of non standard temperature.

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 Mar 06, 2014

    You are correct that the altimeter will read higher than MSL altitude under these circumstances. However, since you can’t adjust your altimeter to the higher pressure, you have to still use the same minimum altitudes as indicated on your altimeter. Since you will be higher at the DH/MDH, you will need a higher ceiling and in some cases a higher visibility to see the runway. For example, if the altimeter setting is 31.20, on a category 1 ILS, you will reach your DH 200 feet higher than you would if you were able to adjust your altimeter. At the regular 200 feet DH, you will be about 2800 (1/2 SM) feet from the threshold. At the point where you indicate 200 feet under these conditions, you will be 6600 (1.25 SM) feet from the threshold. So if you expect to land under these conditions, you will need greater visibility. Also if the reported ceiling is 200 feet, you will still be in the clouds at 400 feet, so to expect to complete the landing the actual ceiling will have to be higher to match your additional height since you can’t adjust your altimeter.

    +2 Votes Thumb up 2 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.