IRS NAV Only

[Guest]

Can anyone help?As shown in the Picture, AUTO is selected, there are VORs all over the place yet the FMC shows IRS NAV ONLY because the radios are not auto tuning. ANy ideas as to why this is happening?Thank you.Lagaz

[Guest Ian_Riddell]

Lagaz...Did the message appear as you were flying through the good reception area... or before? (If before, I believe the message in the scratchpad has to be manually cleared even though updating is now taking place).Unlikely, but all of those stations on your EHSI might be VOR-only stations (no co-located DME's). VOR alone will not give you a radio fix.Other things that might prevent Autotuning, but unlikely in your case:*Bad geometry. If both stations are abeam of your position (on either side of the aircraft), they will not be used for DME updating. Looking at your RDMI, it looks like the autotuned VOR-DME stations are in this position, but the FMC would probably switch to a VOR-DME fix if this was the case... or use one of the other stations.Stations which are too close to the aircraft are not used by the FMC.*There exists the possibility of manually inhibiting stations via the FMC. I can't recall if this is modelled in PIC however.I don't know if the PIC DME's are 5-channel "scanning" DME's. If they aren't, then you may have manually tuned both VOR/DME's (via the CDU) to out-of-range stations, preventing the FMC from tuning the local VOR-DME stations. With 5-channel Scanning DME's, you can still manually tune VOR's via the CDU and the FMC will autotune the other channels for radio updating if the manually tuned channels are out of range.There are probably other clues in your pic, but I may be missing them.Anyway, hope this helps.Cheers.Ian.

[Guest]

Hi,Thanks for the reply.When I got the message, there were VORs around. I manually tuned to one after and it worked .....then I tuned VOR2 to another and that worked. They remained tuned until out of range.......then stopped again, then a while after, IRS NAV only came up again. About an hour later, the radios started autotuning again. And everything worked fine. Go Figure.......Thanks anyway.Lagaz.