STBYRUD
13th Jan 2015, 15:17
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?