Just wondering what this means...My amber FMC light is lit, and the FMC is displaying the message "Scanning DME Fail". I looked up "FMC/CDU Alerting Message" in the Quick Reference Guide (Chap. 11.6), and it just says to "Take action as needed by the message". I checked the "Failures" Menu and it says there are no current active failures, so it must be something I did or something.

 

I'm sure I can just clear it out, but if I did something to cause this, I'd like to know what I did, so I don't repeat the mistake in the future. Anybody know what this means and/or what causes it?

Sorry I can't help with why you don't see the active failures in NGX. But the meaning of it is that both scanning DME radios (two scanning DMEs on NG) have failed and so there won't be any more automatic radio position updates - GPS updates only. The only course of action is to verify (and regularly monitor) your position and this is best done by manually tuning a VOR/DME, selecting indicated the radial on the MCP and checking that the ND map page corresponds (the course intersects the aircraft symbols nose at the right distance. The technique confirms the FMC position matches the actual navaid position.

I've seen this message when I was out of the nearest DME.

This happened at PKWA....smack dab in the middle of the Pacific, so that was most likely the cause. Thanks for the quick replies, guys!

Odd. I never see that message when I'm in Class II Nav over the Pacific. You just notice at some point that the RNP goes to 10.

I allways get that message at TNCM (VOR-DME) and EKVG. (ILS-DME). I seems to be linked to specific beacons and not to an aircraft failure.