B737 NG EGPWS test

[Synthetic]

Evening Ladies and Gents

Just wandering if anyone can shed a little problem. If you select test from the EGPWS control panel with the IRSs both off, no terrain video is shown on the displays. If the IRSs are turned on during a test, after about ten seconds the video appears. If they are on before the test is selected, the video is there from the start. It is as if the EGPWS requires some validity flag from the IRSs. Any avionics aces out their know if this is the case?

Would appreciate your help as I don't have enough documentation here to prove one way or the other.

[QAVION]

Sounds like the weirdness that goes on with TCAS traffic displays on the 747-400...

TCAS displays will not appear on the ND unless the IRS's have been aligned. However, the TCAS traffic displays don't always disappear when you switch the IRS's off (on some aircraft). It's as if the displays need to see a valid IRS signal one time only.

The results vary with which ND mode you are in (VOR/ILS/MAP), TCAS Computer types, what reference is being used (Track or Heading), etc. The traffic will disappear completely however if you switch the TCAS off and back on again without IRS's.

Just out of interest, Synthetic, what reference does your Map use... HDG UP or TRK UP?

Regards.
Q.

[Synthetic]

Thanks for the reply. Ours is actually a simulator, so trk up/hdg up is one of a baffling array of things which vary from one customer. The kinder ones actually tell us what they want in advance:)

[Sperm Bank]

I think you will find that as the terrain comes from the data base, until the a/c knows where it is, it cannot test correctly. The same applies for the TCAS test. The IRS's control the PFD/ND's etc so until they are erect, not much can be tested.