Downunderontop From Hong Kong, joined Jan 2008, 3 posts, RR: 0 Posted (7 years 4 months 3 weeks 3 days 13 hours ago) and read 2462 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.
MDorBust From , joined Dec 1969, posts, RR:
Reply 3, posted (7 years 4 months 3 weeks 3 days 2 hours ago) and read 2367 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.
Acabgd From Serbia, joined Jul 2005, 671 posts, RR: 0
Reply 4, posted (7 years 4 months 3 weeks 2 days 18 hours ago) and read 2273 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".
WILCO737 From Greenland, joined Jun 2004, 9250 posts, RR: 76
Reply 5, posted (7 years 4 months 3 weeks 2 days 17 hours ago) and read 2268 times:
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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 But best would be: no emergency at all!
CosmicCruiser From United States of America, joined Feb 2005, 2263 posts, RR: 15
Reply 6, posted (7 years 4 months 3 weeks 1 day 4 hours ago) and read 2121 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.
Avioniker From United States of America, joined Dec 2001, 1109 posts, RR: 11
Reply 8, posted (7 years 4 months 2 weeks 6 days 6 hours ago) and read 1973 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.
One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533