Another quirk of the 747

[Robert3512 21]

I've realised that the more I fly this majestic beast of an aircraft, the more quirks I discover.

For example, when I tune the VHF3 radio out of BATA and into 121.500, I've noticed that both VHF1 and VHF2 radios will automatically monitor VHF3's GUARD frequency, and the "VHF DATA OFF" EICAS message displays. Is this a unique property of the 747-400? Or did I just not notice this on the other PMDG aircrafts?

[berts 97]

8 hours ago, Robert3512 said:

I've realised that the more I fly this majestic beast of an aircraft, the more quirks I discover.

For example, when I tune the VHF3 radio out of BATA and into 121.500, I've noticed that both VHF1 and VHF2 radios will automatically monitor VHF3's GUARD frequency, and the "VHF DATA OFF" EICAS message displays. Is this a unique property of the 747-400? Or did I just not notice this on the other PMDG aircrafts?

Have another look at your radio and ACARS settings.  The EICAS Memo message "VHF DATA OFF" means the VHF C radio is in voice mode and not available for ACARS data communication.

Bertie Goddard

[Qavion2 39]

14 hours ago, Robert3512 said:

I've noticed that both VHF1 and VHF2 radios will automatically monitor VHF3's GUARD frequency,

This doesn't sound right to me. What do you mean by monitor? Are you saying that with only the L and R VHF receiver buttons selected on your Audio Selector (Control) Panel, that you get 121.5 audio through your headsets or speakers?

You haven't pushed the rectangular transmit button for the Centre VHF on any of your audio control panels have you?

[Robert3512 21]

I mean that the little knobs below the gray rectangular button are lighted green for VHF3 on the VHF1 and 2 radios automatically and I can't switch them off.

[Captain_Al 66]

Yes, this is normal. If you select 121.5 on any radio tuning panel in the active frequency window, you will automatically trigger the guard function on the audio control panel receivers for that radio. They will illuminate green and you cannot deselect them. All audio control panels will now monitor the 121.5 frequency for that radio.

As far as I know, all Boeings do that. I know the 747 and 787 do that, those are the jets I am rated on, I assume it does it on the 777 as well.

Nice exploring Robert to discover that!

[MarkJHarris 128]

737 doesn't. But then it's a steam driven relic....

[Robert3512 21]

14 hours ago, Captain_Al said:

Yes, this is normal. If you select 121.5 on any radio tuning panel in the active frequency window, you will automatically trigger the guard function on the audio control panel receivers for that radio. They will illuminate green and you cannot deselect them. All audio control panels will now monitor the 121.5 frequency for that radio.

As far as I know, all Boeings do that. I know the 747 and 787 do that, those are the jets I am rated on, I assume it does it on the 777 as well.

Nice exploring Robert to discover that!

Thanks, I presume this is a safety feature? Also, on the VHF3 note, what does BATA stand for?

[Qavion2 39]

15 hours ago, Captain_Al said:

Yes, this is normal. If you select 121.5 on any radio tuning panel in the active frequency window, you will automatically trigger the guard function on the audio control panel receivers for that radio. They will illuminate green and you cannot deselect them. All audio control panels will now monitor the 121.5 frequency for that radio.

Normal on 744 airlines fitted with this (real world) option  I discovered this feature on Malaysian Airlines (I recall) and it took me a while to figure out what was going on when I couldn't extinguish the green light on the #3 receiver

[Captain_Al 66]

1 hour ago, Robert3512 said:

Thanks, I presume this is a safety feature? Also, on the VHF3 note, what does BATA stand for?

I think you mean "DATA", the center VHF radio is normally used for ACARS and Data Link, when you took it out of DATA and tuned to 121.5 MHZ, now you took the Radio Tuning Panel out of Data Link and tuned it to a frequency, in this case the emergency guard frequency. That triggered all the Audio Panels to receive and be locked to receive on the C VHF. 

Yes, it is a good practice and a safety technique to monitor guard in case you would pick up an ELT or some other type of signal and report it. Also, if you missed a frequency change, eventually ATC might try the guard frequency to reach you.

[Captain_Al 66]

4 minutes ago, Qavion2 said:

Normal on 744 airlines fitted with this (real world) option  

Yes, I think you are right John, it was on every airplane I have been on, but some FCOM's do not mention it, so I believe it is an option. On the 787 I am not sure, I think it is standard on that airplane.

[MarkJHarris 128]

Normal practice though is to use VHF 1 for all ATC comms, VHF 2 on 121.5 and VHF 3 on DATA. Of course if you work the company I do, DATA  is pointless as they won't pay for ACARS service. Thus we can't get weather on it and use VHF 3 for 121.5 and VHF 2 for VOLMET and ATIS and any company transmissions we do.