View Full Version : B777 Alternate Nav

23rd Jan 2010, 13:22
Hey everyone,
hopefully someone knows the answer; I've searched the manuals and can't find it. When you lose both FMC's you still have alternate nav through the CDU's. Providing the adiru is still serviceable its still mnps compliant. But what is the rnav capability, is it still ok for b rnav airspace above FL95…ie rnp 5? What is it certified for?

23rd Jan 2010, 14:54
backup Nav are using the memorized flight plan in the CDU (or MCDU for Bus)
Backup has no connection the the Navdatabase, so any reference made to a Waypoint will not work, however you will see the ccordinates of these waypoints, it is just like an IRS system so use it as such.
BTW seabiscuit was a famous horse ;)

23rd Jan 2010, 16:23
Hey K,
thanks for your reply,
I appreciate all you said, but if you enter the waypoints as lat/long (a la old ins system) do you know what the certified ANP is?

23rd Jan 2010, 19:35
ANP, is actually elaborated by the FMS on the AIRBUS and most probably by AIMS on B777 (I have to check this out) so if both FMC are inop you cannot have an ANP.
But you can enter lat and long.
You could use your GPS position versus your Backup position to see how far apart they are from that deduce if your are within the RNP "tube" here I am thinking RNP 4.

But unfortunatly these things cannot be tested unless the FMC are inop:ouch:...
I will try in the sim. :E