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Thread: B737 @ Aberdeen
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Old 13th Dec 2021, 11:13
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Originally Posted by fdr View Post
That is quite correct. It has a curious 2 APLT 3 IRS reference architecture that provides for the fail-operational capability. With 2 APLT and without the option, it is fail passive with 2 APLTs. There is a note in the FCTM for the plane that says, for single-channel ops, refer to limitations section of the AFM, and in most cases that requires a single channel to be disconnected no lower than 50ft AGL, for FAA and 158ft AGL for EASA....
Yup, pretty much the same as the A320, which uses a two autopilot and three full IRS (737 uses two full IRS and one ARS) system. The three autopilot thing had to be used in the past, technology has evolved and two are enough now. The 737 fail operational system is actually more modern than the A320 one, by around 15 years. Still, the operation is in many ways hampered by the insistence on single channel approaches which is neither necessary nor clever. Although, to be honest it wouldn't have made a difference in the original case of this thread.
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