i don;t understand: i am at FL 396. the AGL is at least 39500ft Why is the terrain display like this?radio update question: at present there is only one DME used for navigation? how can one DME know where the plane is? thanks

:( The airplane can not autotune second station, because radio is in manual mode. It uses VOR/DME update now.

what about this? is the radio is being tuned? if not, how can the radio coordinates be shown on the page in the right CDU?

Edited February 2, 201214 yr by sunxuyang

Is this the situation with inactive VNAV? Because you are in CWS mode and in ALT HOLD mode, while you should be in CMD and VNAV SPD.I am not sure what the radio position shows when you have no radio in range, maybe last known radio position + FMC position movement?

FMC uses its autotuned DME stations, it will do by using the internal database, comparing its actual position, and tuning 2 different stations selecting the best ones. The process is fully automatic and with no pilot input required (the station maybe or not tuned in the panels)

Is this the situation with inactive VNAV? Because you are in CWS mode and in ALT HOLD mode, while you should be in CMD and VNAV SPD.I am not sure what the radio position shows when you have no radio in range, maybe last known radio position + FMC position movement?

no i don't think it has anything to do with the CWS. because it is about position updating.if there is no radio in the range, according to the FCOM the FMC is using GPS and IRS postions!

FMC uses its autotuned DME stations, it will do by using the internal database, comparing its actual position, and tuning 2 different stations selecting the best ones. The process is fully automatic and with no pilot input required (the station maybe or not tuned in the panels)

But the problem is as you can see in the pic, no radio updating is being done, how can the radio position (on the right fmc) continues to provide corrdinates?

The FMC position is currently based on DME (XDX), the manually tuned VOR (BTO) and the two IRS.Out of interest, why have you switched off the GPS?Terrain is in Peaks mode - when you are high above terrain (need to check the FCOM for actual conditions) the EGPWS still return absolute values rather than relative values. This is to give situational awareness in case of emergency descent. Normally, I would just turn it off for the cruise to declutter.

Edited February 3, 201214 yr by davidz

If you look at FCOMv2 it's possible to have two FMS. In that case the left one is primary and will therefore auto tune the DME's, make the calculations and then pass the info to the second FMS. If you look at the screenshot above you can see that the left system has tuned two stations and therefore if PMDG have simulated dual FMS then the green "FMS L" makes sense ( see p 11.30.2 FCOMv2).

no i don't think it has anything to do with the CWS. because it is about position updating.if there is no radio in the range, according to the FCOM the FMC is using GPS and IRS postions!But the problem is as you can see in the pic, no radio updating is being done, how can the radio position (on the right fmc) continues to provide corrdinates?

The left CDU shows four DME frequencies that the system can tune and get range information and hence a radio position. The fact that the two manually tuned VHF NAV receivers aren't tuned to an in range signal is not relevant.

The priority order for the FMC for position update count in the second position the DME DMe autotuned by the FMC itself, the first one is the ADIRU/GPSThe FMC will not use 2 DME station within 30 or over 150° from the other as the position will be not precise. Vor manually tuned frequencies tunes the relative DME for pilot display reasons (VOR DME can be used by FMC if no other DMEs are avaiable, this reverting from DME DME to VOR DME)

why have you switched off the GPS?

in china GPS is not accurate!

in china GPS is not accurate!

GPS is accurate. It's the surveying that is suspect. WGS-84 is not adhered to in many places. When you line up on the ILS28 at Dalian, for example, the ND shows the runway a mile or two offset. Not reassuring.

FMC uses its autotuned DME stations, it will do by using the internal database, comparing its actual position, and tuning 2 different stations selecting the best ones. The process is fully automatic and with no pilot input required (the station maybe or not tuned in the panels)

Huh, I was wondering why they left the AUTO/MAN switchbutton, now I know :) It actually just occured to me as I looked at the nav status page as I am flying now.

While flying in zones with high density of airports you will see that the tuned stations will vary very often.