RVSM altimeter crosscheck B777
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RVSM altimeter crosscheck B777
Hello everyone, call me pedantic, but the other day in cruise I had nothing better to think about than the following: the regulation concerning RVSM operating procedures (such as SPA.RVSM.105 from the EASA) requires the flight crew to record the primary and standby altimeter readings before entering RVSM airspace. Back on the 737 we used to crosscheck the main and standby altimeters on the ground, as well as in the air, with the well known maximum difference of 200ft between primary altimeters in cruise.
On the 777 now my operator has us do the same, but this strikes me as absolutely pointless since the left and right PFDs will ALWAYS show the same altitude and speed thanks to the ADIRU first correcting the three static and pitot pressures from the respective ADMs and then voting on the most plausible pressure to convert into a single altitude and speed output to be used by various user systems. I guess since the ADIRU will reject one unreliable source and only throw a SGL SOURCE AIR DATA caution message when its down to one useable source this satisfies the RVSM altimeter crosscheck requirements without the need for any crew checks?
On the 777 now my operator has us do the same, but this strikes me as absolutely pointless since the left and right PFDs will ALWAYS show the same altitude and speed thanks to the ADIRU first correcting the three static and pitot pressures from the respective ADMs and then voting on the most plausible pressure to convert into a single altitude and speed output to be used by various user systems. I guess since the ADIRU will reject one unreliable source and only throw a SGL SOURCE AIR DATA caution message when its down to one useable source this satisfies the RVSM altimeter crosscheck requirements without the need for any crew checks?
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Even on the B737, if the Capt and FO primary altimeters disagree more than 200ft an ALT Disagree will appear on the PF.
Kinda pointless really. I can understand on older aircraft why we do it though.
Kinda pointless really. I can understand on older aircraft why we do it though.
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My point is that at least there are values to compare on a 737, 757, 747, or any other airplane of that generation... An altitude comparator is one thing, but only presenting one (albeit smartly chosen) value to the pilots is another. I am curious, do current Airbuses also do something similar?
Last edited by STBYRUD; 16th Jan 2015 at 18:25.
