TWR/GMC VHF-UHF Cross-coupling

[Mooncrest]

Quick enquiry. At MAN, the respective TWR and GMC VHF and UHF frequencies are fully cross-coupled so all stations, whether a/c, vehicles or ATC can all monitor one another. At LBA the same voice switch (Schmid) is used but without a full cross-coupling facility. This means that TWR can hear a/c and vehicles, vehicles can hear TWR and a/c but a/c can only hear TWR, with the result that vehicles' TX frequently gets stepped on by aircraft.
Seems a daft way of doing things. Can anyone shed any light on why this is ? Beats me. :confused: Thankyou.

MC

[Comms Boy]

but a/c can only hear TWR

Sounds right to me. The TWR is the only RT the Pilot needs to concentrate on.

[hangten]

No, I agree that this isn't the ideal situation since it reduces a pilots situational awareness of vehicles, which I would suggest is extremely favourable in a runway safety environment. Also, as you say, it increases the likelihood of crossed transmissions when one party can't hear another, another potential safety issue at worst and irritating at best.

I expect that it's an engineering equipment limitation and that there is almost certainly a cost implication. However, all you can do is request the change and see what response you get. It may simply be that no-one has raised the issue, or at least connected it to safety enough to get a satisfactory response.

It's probable too that this situation is not solvable in it's entirety since any reasonable sized aerodrome is likely to have areas which are blind to each other, even when all areas are within range of the tower.

[Spitoon]

Usual argument is that it prevents vehicles (sometimes with less disciplined RTF usage) blocking aircraft transmissions. Depends a bit on how busy the airport is and the frequency configuration but in my view ideally there should be complete cross-coupling on GMC for vehicles on the manoeuvring area and transfer to AIR frequency for vehicles crossing or operating on runways. When I last had any involvement with this the CAA expected the airport operator/ATS to define what they wanted and to argue why this was most appropriate so each airport comes up with a slightly different arrangement.

[2 sheds]

The TWR is the only RT the Pilot needs to concentrate on.

In an ideal world, perhaps, but that is rather lacking in either imagination or experience.

2 s

[Mooncrest]

I agree in so far as in the air, a pilot only needs to receive RT from ATC and also from other aircraft, for receipt of instructions, advice and for the aforementioned situational awareness. However, it is a fact that on the ground, vehicles are likely to be on the manouvering area and should be regarded as "traffic" (sorry, can't think of a more suitable categorisation here). I guess many pilots would like to see AND hear what these vehicles are doing rather than solely relying on ATC for this information.

IIRC, when the current voice switch was installed at LBA in 2005, there was a complete cross-coupling facility for the first time at the airport. I think it's only in recent months that the facility has been reduced to its current "two thirds" status. It may be down to an equipment failure but I doubt it after all this time and I can't see the facility being withdrawn for cost reasons. Perhaps it was a pilot-driven decision.

By the way, I say all this from the point of view of a tug driver with a local RT licence. My transmissions have been stepped on more than once ! As for RT discipline, it is on the whole of a good standard at LBA. There is at least one semi-retired ATCO involved in the training and the ASU make you work for your annual validation, as would be expected.

[HEATHROW DIRECTOR]

It's absurd and, IMHO, potentially dangerous if all users of a frequency cannot hear all others, including those on a coupled frequency. If pilots cannot hear tugs and other vehicles on ATC frequencies it surely gives rise to QRM when two stations transmit at once but cannot hear each other?

Where I once worked, vehicle drivers received proper training from the ATC Training Unit and their discipline on "our" frequencies was impeccable.

[rich_g85]

Ah, I wonder if a similar system exists at Bournemouth? Many times I hear the Tower call a Safety/Ops/Shell/Esso callsign and I never hear the reply. I always just assumed this to be because the radios used by the vehicles had a lower transmit power.

[Mooncrest]

Matters are further complicated at LBA by the fact that there is no GMC. To digress a little, the amount of traffic during daylight certainly warrants GMC but the present shortage of taxiways makes it impractical. Therefore TWR handles all aerodrome traffic (except when the Delivery position is open) with the result that a significant amount of RT is handled by a single controller. The likelihood of ground vehicles and a/c transmitting simultaneously means that messages may require repeating, partly or in full. Not an ideal situation for a busy ATC position.

On the other hand, certain Aerodrome Authority vehicles (e.g. Checker, Tels, Fire) are granted "free-ranging" status on certain parts of the manouvering area, which I guess is similar to "own look-out" at MAN. This must help a little.

As for Bournemouth, I wouldn't be surprised if the TX/RX switch was similarly configured to that of LBA hence the same situation described at that airport. I don't think transmitter power would be significant: most handhelds give at least 4W and vehicle mobiles more. In any case, there would be a UHF to VHF repeater somewhere on the airfield to provide complete coverage.

I maintain that it doesn't make sense to have only a "semi-operative" cross-coupling facility which seems to be the consensus on this thread so far.

MC

[Neptune262]

It is a measure used at some airports. It is supposed to increase the situational awareness to pilots, as they then know that vehicles are cleared onto certain areas of an airfield, as they hear the ATCOs transmissions, whist avoiding that potentially non-RTF licenced ground staff do not block, or transmit on, a licenced VHF frequency. Also may be relative to the types of frequencies and equipment available at the airfield for the ground staff.

It is not ideal, as all staff adequately trained, operating on the same frequency would be the safest operational situation.

[On the beach]

Sounds like they need to employ more staff.

[Mooncrest]

Certainly the obvious thing to do would be to ensure that all staff who use airfield RT have been thoroughly trained and standards are maintained. Then it's okay for all stations to be able to hear each other without running the risk of sub-standard RT discipline. Arranging the voice switch so a/c can only hear half the conversation, as it were, is crackers. It's like having a telephone with no earphone in the receiver. Can I speak yet ? Is it my turn ?
Has the other bloke gone quiet ? And so on...

To be fair to LBA, as I've alluded to in a previous post, high RT standards would appear to be a target, given that allowing anyone on the manouvering area who isn't an airport company employee is a relatively recent direction for LBA. Really. When I started there in 1996, crossing the runway or going on the taxiways meant arranging an escort from the Fire Service or occasionally, ATC. There was no Airside Operations or Safety Unit and no RT training for a/c engineers etc. Things have obviously moved on since then and with some necessity. But I still wish we had the full cross-couple thingummyjig. :(

[Captain Smithy]

VHF-UHF/UHF-VHF X-Couple will usually be selectable by the controller unless the voice switch is configured only to give VHF-UHF. Various reasons - equipment design, reducing VHF traffic, etc.