Welcome Guest. Sign in or Signup

3 Answers

40:1

Asked by: 6464 views Commercial Pilot, FAA Regulations, Flight Instructor, General Aviation, Instrument Rating

Can anyone plz explain what is 40:1 rule for IFR flight?

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. John D Collins on Sep 30, 2016

    I am not aware of a 40 to 1 rule for IFR. There is a 40 to 1 slope used to evaluate obstacle clearance on departures and climb. Standard IFR climb rates of 200 feet per NM are assumed, so 40 to 1 is 151.9 feet/NM, providing 48.1 feet of clearance for each NM if an aircraft climbs at the standard performance rate/NM.

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes



  2. david4790 on Sep 30, 2016

    Yes i mean the 40 to 1 slope. So for every 1 feet we will have obstacle clearance of 48 feet if we maintain standard climb 200NM?

    -1 Votes Thumb up 0 Votes Thumb down 1 Votes

  3. Best Answer


    John D Collins on Sep 30, 2016

    Well sort of. I assume you meant for every one NM there is a 48 foot buffer, That 48 feet per NM is cumulative, so at 2 NM, it is 96 feet, and at about 21 NM it adds up to 1000 feet, which is the standard obstacle clearance used when enroute (except in the mountains).

    +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.