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Adam106

Fail Operational oddities

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I'm not sure how many have delved into the fail operational autoland logic in the NGX (or how many want to!) but I've been experimenting tonight with a few things, and some odd things have come up.

 

It seems to be that the airplane is happy to engage and continue with LAND 3 even with 1 ILS receiver failed. When I fail one ILS I get a 'No Autoland' message on the engine display - as expected. I'm then expecting the autoland status indicator on the PFD to say 'NO AUTOLAND' when passing 1500' RA. It doesn't - it engages in LAND 3 and does the autoland. Should this happen?

 

In another failure situation I fail the standby ISFD. I get a 'NO LAND 3' on the engine display - all good. I also get the 'LAND 2' on the PFD when passing 1500'. This is as expected, and all fine. However if I fail the standby ISFD after 'LAND 3' engagement at 1500' I don't get a reversion to 'LAND 2' (the autoland message on the engine display does read NO LAND 3, but no PFD change) Surely we should get this downgrading of status, or have I read the systems wrong?

 

The only failure that generates the 'NO AUTOLAND' on the PFD is if I fail one of the radio altimeters below 1500' - are there any other failures that should cause this reversion? I expect there might be.

 

Complex and rivet counting to a certain extent, but it just shows the level of detail the NGX incorporates...

 

Adam Turley

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The system is rigged so that while you can not normally engage it (or maybe you can, I am not 100% sure. Either way you should not), it will be able to carry on on one system.

 

The reason for this ability is really the same reason why you engage both radios and autopilots etc. - so one can take over if the other fails.

 

The reason why single RA failure kicks the whole thing out... I dont know. Might be that RA can not self check other than crosscheck, and RA is the critical source of data for the very last phase - when you have no other choice but to land. Doesnt help if you find at 30ft AAL that the airplane is not flaring...


--Peter Fabian 
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