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14. Propulsion

In a FADEC system, active control switchover occurs

  • on shutdown.
  • when channels A and B are healthy.
  • on engine startup only.

Explanation from PART66Online

In a dual-channel FADEC the two channels alternate as the active controller, with the changeover normally made at engine start so that one channel runs the engine for the cycle while the other stands by. Switchover is not performed continuously while both channels are healthy in flight, nor on shutdown.

C

Crystal asked · 7 May 2016

I think the correct answer is ON SHUTDOWN.
I found the below explanation from a different site.
On the CF6 FADEC, each startup uses an alternative channel.But the switch-over occurs on shutdown of the previous run.The reason for this is that the switch-over at start up might interrupt the start-up sequence.

Community Comments (1)

A
ademceven 19 Feb 2020
yep you are correct, in documents this subject poorly mentioned, usually documents says that "Active/Standby transfer will occur after the engine has been run above 76% N2 and subsequentl yshutdown (N2 less than 35%)" this is confusing people. an engine has to pass 76 percent n2 speed, in order to register that attempt as an "engine cycle" means engine started normally. upon shutdown of engine the fadec changes channels will change from a to b for next cycle (assuming both channels have equal health regarding control)

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