Welcome Guest. Sign in or Signup

1 Answers

What is the orgin for the blocked static port rule-of-thumb

Asked by: 4936 views , ,
Instrument Rating

Static instruments - when the normal static source is blocked and you use the alternate inside the cabin I have been told to use the 7/7 rule. The Airspeed indicator will read 7kts faster and the altimeter will read 70ft higher. Do you know how these numbers came about or any more information on it?

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. Matthew Waugh on Jul 30, 2010

    I’m going to go with you as the origin – although apparently you can trace it back at least one more generation.

    I have never heard that. I have always been told that when on alternate static the instruments will not be accurate. I seem to recall from my ground school training on one plane that the manual had specific values published, but since I wasn’t required to memorise them for any test I never knew them, as opposed to a lot of information that I have retained for 24 hours and then forgotten.

    I think your information is a lot more useful than “not accurate”, but if your information is not accurate then perhaps it is no more useful. If I had a blocked static port and my only option was to shoot an ILS to minimums where 70 ft. was going to make the difference then my goal would have shifted to having my accident on the airport, as close to the fire station as possible and consider any improvement on that a bonus.

    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.