Welcome Guest. Sign in or Signup

3 Answers

Pitot blockage but drain hole NOT blocked

Asked by: 13756 views , , ,
Aircraft Systems

If the pitot tube inlet becomes blocked but the drain holes remain open (if this is possible) won't this essentially cause the AS indicator to read close to zero if the pressure in the chamber is equalized through the drains? Are there one way valves involved? It seems that the answer I see everywhere is that when the pitot inlet is blocked the system will act like an altimeter. Is that always the case? Thanks and need to know before my instrument practical this weekend.

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. Brian on Oct 26, 2011

    You have it right. The sources you’ve read are referring to a complete blockage. Three possibilities:
     
    Just pitot blocked — ASI reads zero because air inside the tube drains out.
     
    Just drain hole blocked — ASI reads erroneously high. By how much I am not certain.
     
    Both holes blocked — ASI reads like an altimeter because air is now traped in the tube and acts just like air inside a water bottle. Ever close up an empty bottle on a commercial flight home only to pick it up on the way out and it’s smashed like a big fat guy sat on it? The trapped air compresses and puts less pressure on the system, ASI reads lower. And vice versa with altitude increase. 

    +5 Votes Thumb up 5 Votes Thumb down 0 Votes



  2. Wes Beard on Oct 26, 2011

    A good website that graphically shows what is happening is here:  It should help cement what you already know.
     
    http://www.luizmonteiro.com/Learning_Pitot_Sim.aspx

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes



  3. songül on Jan 05, 2014

    Hi, I have some question about pitot static tube. I know ıt has drain hole for water but ı dont know ıts structure. In other words how does drain hole work. ıt drain water how. Static chamber and total chamber have got same drain hole? Plese you help me 🙂

    0 Votes Thumb up 0 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.