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MD11 Avionics  
User currently offlineDownunderontop From Hong Kong, joined Jan 2008, 3 posts, RR: 0
Posted (6 years 6 months 3 weeks 6 days 8 hours ago) and read 2199 times:

Has anyone heard about the MD11F air speed indicators beeing finicky e.g. the air speed indicators (dual) indicating different speeds some 100 knots but only for a few seconds. Not sure how this could happen. This was told to me by UPS pilots flying into HKG.

downunderontop

9 replies: All unread, jump to last
 
User currently offlineAcabgd From Serbia, joined Jul 2005, 659 posts, RR: 0
Reply 1, posted (6 years 6 months 3 weeks 6 days 3 hours ago) and read 2172 times:

Happens on other aircraft as well sometimes. MD-11 PFD displays a warning messsage when this happens.


CSud,D9,MD8x,D10,Trid,BAC1,A30,31,319,320,321,33,346,B71,72,73,74,75,76,77,L10,S20,A42,A72,T13,T15,F50,F70,F100,B146
User currently offlineWILCO737 From Greenland, joined Jun 2004, 8968 posts, RR: 76
Reply 2, posted (6 years 6 months 3 weeks 6 days 2 hours ago) and read 2165 times:
AIRLINERS.NET CREW
HEAD MODERATOR

I have never seen that or heard about that...

WILCO737 (MD11F)
 airplane 



It it's not Boeing, I am not going.
User currently offlineMDorBust From , joined Dec 1969, posts, RR:
Reply 3, posted (6 years 6 months 3 weeks 5 days 21 hours ago) and read 2104 times:

Theoretically any aircraft could have instruments go wanky. That's why pilots are trained to cross check instruments against each other to make sure they aren't fibbing. Could a UPS MD-11 have suffered a condition that would cause one airspeed indicator to run wild? Suppose so. It's not a problem that I've heard of common to the type though.

User currently offlineAcabgd From Serbia, joined Jul 2005, 659 posts, RR: 0
Reply 4, posted (6 years 6 months 3 weeks 5 days 13 hours ago) and read 2010 times:



Quoting MDorBust (Reply 3):
That's why pilots are trained to cross check instruments against each other to make sure they aren't fibbing.

That's also why, as I mentioned, a warning appears on the display if such an event occurs. However, I also have not heard of this being anything MD-11 specific and/or the airspeed indicators being "finicky".



CSud,D9,MD8x,D10,Trid,BAC1,A30,31,319,320,321,33,346,B71,72,73,74,75,76,77,L10,S20,A42,A72,T13,T15,F50,F70,F100,B146
User currently offlineWILCO737 From Greenland, joined Jun 2004, 8968 posts, RR: 76
Reply 5, posted (6 years 6 months 3 weeks 5 days 12 hours ago) and read 2005 times:
AIRLINERS.NET CREW
HEAD MODERATOR

Thats why we have more than just one airspeed indicator... one on the CP side, one on my (FO) side and the standby airspeed indicator! That makes 3! And you can somehow judge your speed with the TAS or GS calculated by the IRS or the ADC... but thats just a guess... It can help as well, if you fly pitch and power! put the power to a specific value and set the pitch, at which you know the aircraft flies properly. Then you can judge which ASI seems to be wrong...
Its a pretty complicated procedure we call "Unreliable Airspeed"... And its something I dont want to encounter in real life! Then I'd prefer the engine failure  Wink But best would be: no emergency at all!

WILCO737 (MD11F)
 airplane 



It it's not Boeing, I am not going.
User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2255 posts, RR: 15
Reply 6, posted (6 years 6 months 3 weeks 3 days 23 hours ago) and read 1858 times:

Never seen it but would suspect possible CADC problems and look for other unrelated warnings. As Wilco737 said check your other a/s ind. If it was just for a second I would contribute it to a "stray electron" and forget it.

User currently offlineN685FE From United States of America, joined Dec 2003, 451 posts, RR: 11
Reply 7, posted (6 years 6 months 3 weeks 2 days 15 hours ago) and read 1765 times:



Quoting CosmicCruiser (Reply 6):
If it was just for a second I would contribute it to a "stray electron" and forget it.

Had this been writen up, it probably would have turned into loading the parts cannon and firing for the sake of t/s. Thanks for not writing it up, save write ups for hard faults (and give details).



psp. lead by example
User currently offlineAvioniker From United States of America, joined Dec 2001, 1109 posts, RR: 11
Reply 8, posted (6 years 6 months 3 weeks 2 days 1 hour ago) and read 1710 times:

Seen it on longer flights a couple of times and once after a wash about three hours out. The write-ups were cleared by "draining the pitot/static drains".
Also had one plane do it back in 96 about every two weeks or so (turned out to be a bad ADC).
The MD-11 is a digital plane so in order for you to have a significant difference in the indications it has to be an input problem and not the indicators (unless, of course, the problem was with the standby indicator which is a stand-alone unit).
The indicators only display the results of a stream of 1's and 0's and any error in input would cause the indication to blank or flag. They work or they don't. The problem would have to be with the sensor or the processor and they're both in the ADC. The only other thing that comes to mind is an obstruction in a pitot or static line that cleared itself. That could easily be icing or an errant bug or whatever.
As to the "Money/Parts cannon", it's drying up. We're going to have to start being careful which way we LEAN in our troubleshooting.
:-(  Smile



One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
User currently offlineAvioniker From United States of America, joined Dec 2001, 1109 posts, RR: 11
Reply 9, posted (6 years 6 months 3 weeks 2 days ago) and read 1708 times:

For the more curious . . .


 

[Edited 2008-01-11 05:58:57]

[Edited 2008-01-11 05:59:38]


One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
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