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787 altimeter inaccuracy

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787 altimeter inaccuracy

Old 19th Nov 2019, 13:32
  #1 (permalink)  
Thread Starter
Join Date: Sep 2011
Location: FL390
Posts: 313
787 altimeter inaccuracy

Just been made aware of (yet another) BAB for the 787 where the altimeter measurement differs between Capt and FOs PFDs because of an FCM fault.

Apparently this can cause altitude excursions of up to 1000ft (great in RVSM airspace...) and we have a new unannunciated checklist to play with.

The thing is, all the training material for the 787 says that air data displayed on the PFDs is voted single-source, so how can one side provide different data to the other?

Is this another "the pilots don't need to know how this actually works" situation?
Fursty Ferret is offline  
Old 19th Nov 2019, 13:52
  #2 (permalink)  
Join Date: Jun 2014
Location: Mordor
Posts: 294
I’ve been told on numerous occasions by Boeing and airline instructors that “altimeters will always show the same, no need to compare them”.

Yet, I’ve seen myself a difference of ~100ft between Capt. and F/O altimeters in cruise, which resolved itself after a few minutes...

My guess is that the system uses voted data from 3(?) independent sources. However, if one of these sources fail, then I suspect each side uses one of the two remaining independent sources.

As you already mentioned, Boeing didn’t bother to provide an explanation to us, pilots.
Sidestick_n_Rudder is offline  
Old 21st Nov 2019, 08:11
  #3 (permalink)  
Join Date: Jun 2001
Location: EUSSR
Posts: 380
Red face

Don´t want to open a new thread, I find the erratic speed indication during take off rather irritating. As if the aircraft doesn´t accelerate smoothly. Which is certainly not the case. I have never seen this on any of my previous aircraft.
wondering is offline  
Old 21st Nov 2019, 15:31
  #4 (permalink)  
Join Date: Jul 2000
Location: Nirvana..HAHA..just kidding but,if you can tell me where it is!
Posts: 340
Yep,me too.
Have more than once pushed the levers forward assuming Windshear..
Yaw String is offline  

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