MLS & Audio Control Panels.

[forget]

Question for avionics - with Audio Controls as below, with ILS/MLS, how is Marker Audio selected? Thanks ahead.

[Fargoo]

Use the L or R VOR listen switches?

[forget]

No one out there? Shortage of avionic guys? Where's Spanners@CX? He'll know.

[Fargoo]

I can only assume that you can't deselect the Marker audio with that type of ACP. The marker is always received and monitored by the left VOR on the 757 regardless of what ACP type is fitted.
The other two types i've seen on our 757's have a seperate audio selector for the MKR.

[forget]

Thanks again Fargoo,

The Marker is always received and monitored by the left VOR on the 757 regardless of what ACP type is fitted.

I didn’t know that. But why then do ‘usual’ 757 panels have a separate Marker select?

I think the panel above is from the BA series of 75s which were modified for MLS trials. With Airbus and MLS ‘provisions’ the ACPs have MLS and Marker. A-320 Below. Still curious, and I'd appreciate it if you'd check the wiring manuals to confirm Marker on Left VOR. Not that I doubt you - just never heard it mentioned before.

[Fargoo]

I can do better than that, how about a quote direct from Mr Boeing!

A. Marker Beacon Receiver Module
(1) The active marker beacon module is located in the left VOR receiver
(AMM 34-51-00). The VOR receiver is located in the aft equipment
center on rack E6-1 or in the main electronic equipment center on
rack E3-2. The module in the right VOR receiver is inhibited.

I'll take a look again next time i'm at work and see if it sheds any light on the ACP's without the seperate marker selection.

[forget]

Good one. I follow that - but the VOR/ILS Ident Audio and the MKR Audio come out of the receiver on separate wires. So what happens to the MKR Audio between the receiver and the ACPs

[forget]

PS.

The marker is always received and monitored by the left VOR on the 757 regardless of what ACP type is fitted.

Fargoo, I have to doubt this. That would mean, on approach when you needed MKR audio, you'd have to listen to the ILS Ident all the way down the Glideslope. No? Am I missing something? Like why does the mystery panel (top) show VOR and ILS, rather than just NAV like everything else?

[Fargoo]

Ok, I had a look today.
The L VOR receiver does utilise it's built in Marker module and sends the audio signal through to all the audio control panels. The work is done inside the ACP.
On the ones with no seperate marker control the audio is fed to the L/C/R ILS/MLS positions and that is how you control the marker audio.

The manual revision for aircraft with these panels fitted states

"The AVTECH Audio Select Panels on ** 757 do not have a Marker control switch. Marker Audio is obtained by selection ILS control switch. "

Incidentally the 767 aircraft I looked at today had the same control panels - ie no seperate marker control.

Hope this clears things up

[forget]

Well done Fargoo, Owe you one.

(PS. I suspect you may have cleared things up for a lot of people!)