Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

B737 Airspeed Unreliable?

Tech Log The very best in practical technical discussion on the web

B737 Airspeed Unreliable?

Old 20th Jan 2021, 18:31
  #41 (permalink)  
Join Date: Apr 2001
Location: various places .....
Posts: 6,683
so could be starting a long way away from your desired speed. Setting normal pitch/power for, say, F5/180kts when you are in reality 40kts+ slower could make things worse, not better.

Wherein lies the value of knowing the numbers. The pilot with that knowledge, first, will identify the present situation, then where the aircraft should be, and set a suitable thrust/attitude combination to effect that change. My observation has been that your concern appears not to be a problem IF the pilot starts out with a reasonable knowledge of thrust/attitude combinations. This all presumes some learning and a reasonable amount of exposure practice to acquire a skill level.

SOPs are important and need to be applied, but there is an advantage in knowing a bit more than the assumed minimum competence level.

rather than seeing someone else set a performance attitude that is not quite what you expected

Which presumes the unhappy situation that both pilots have been asleep ?
john_tullamarine is offline  
Old 20th Jan 2021, 19:46
  #42 (permalink)  
Join Date: Dec 2003
Location: Tring, UK
Posts: 1,535
SOPs are important and need to be applied, but there is an advantage in knowing a bit more than the assumed minimum competence level.
Absolutely with you there.

I think there is a big difference between a UAS exercise in the sim when itís expected and something that creeps up on you in real life. Pitot/static blockages or leaks are a good example, as initially everything works and there can be a slow degradation which is difficult to pick up considering the tolerances. When you add in temperature, weight, wind component changes, temperature inversions, turbulence, etc. it can be hard to diagnose. Consider the effect of flying in/out of a jet stream: you get performance attitudes that are well outside what happens in a steady state but accept that because, well jet stream. Symptoms not unlike kinds of UAS but we accept them as normal.

One of the clues that all may not be well is that on FMC aircraft the calculated wind starts changing but this happens when everything is working as designed but the w/v is actually changing.

What Iím trying to say in a very long-winded way is that yes, a working knowledge of performance attitudes is useful and good airmanship, plus will probably help you diagnose a fault condition earlier than someone who just follows the flight director to wherever it goes, but itís not a panacea. By the time youíve twigged that things really arenít what they should be, especially in a time of high workload, you may not be quite where you think you are, like when the GPWS goes off. The checklist assumes that youíve lost some SA and need a bit of time to rebuild it, which is what it gives you.

Also, given that pretty much all manufacturers publish a UAS checklist, you would be putting yourself well out on a limb if you decided not to follow the first vital actions and roll your own. Assuming you survived, that is...
FullWings is online now  
Old 20th Jan 2021, 23:02
  #43 (permalink)  
Join Date: Jun 2006
Location: Brisbane
Posts: 166

Knowledge of pitch and thrust for phases of flight, along with constant awareness of pitch and thrust will help to identify the problem.

Upon identifying the problem, follow the checklist. It works.

Many airliners have crashed recently because nobody on the flight deck actually identified the problem.
Derfred is offline  
Old 26th Jan 2021, 16:44
  #44 (permalink)  
Join Date: Oct 2006
Location: Ankh Morpork, DW
Posts: 612
Airspeed Unreliable NNC

6. Nuisance Stick Shaker Canon Plug . . . . . . Disconnect

ImbracableCrunk is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.