Welcome Guest. Sign in or Signup

1 Answers


Asked by: 6847 views , ,
FAA Regulations, Instrument Rating

Normal 0 false false false MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;}

The following is stated in the air traffic control procedures; what does it mean to the pilots?


When the prescribed minimum altitude for IFR operations is at or above 18,000 feet MSL and the atmospheric pressure is less than 29.92”, add the appropriate adjustment factor from table 4−5−3 to the flight level equivalent of the minimum altitude in feet to determine the adjusted minimum flight level.

Altimeter Setting        Adjustment Factor

29.92” or higher          0000 feet

29.91” to 29.42”         0500 feet

29.41” to 28.92”         1,000 feet

28.91” to 28.42”         1,500 feet

28.41” to 27.92”         2,000 feet

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. Wes Beard on Jun 30, 2013

    The altimeter setting you place in the Kollsman window is based on the sea level pressure for the area you are flying in. Hence, if you were to be at sea level the altimeter will read zero.

    The sensitive altimeter is calibrated to sense decreasing pressure and through fears and linkages show a different altitude than zero. For every 1″mb drop in pressure, the altimeter will read one thousand feet higher.

    At 18,000 ft MSL the outside pressure will be around 12″mb. Since the altimeter is set to read sea level pressure we set inside the Kollsman window the sea level pressure and the alyimeter will read 18,000 feet.

    If the sea level pressure is lower than 29.92, the flight levels (based on 29.92) will start higher. See 91.121 showing the minimum flight level based on sea level pressure.

    Lastly, aircraft flying in the flight levels aren’t worried about hitting terrain but other aircraft. To solve that problem, all aircraft set the same altimeter setting so they can compare their altitude with other airplanes.

    +1 Votes Thumb up 1 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.