HF Air Traffic Control And VOLMET
An area of listening for the genuine enthusiast and an opportunity for the writer to offload more old gags. For example, the last time your scribe was on an aircraft he sat next to the rear gunner.
One Of Our Aircraft Is Missing
There will be those who have come to our hobby from the Services. There will be pilots and ground crew who want to keep in touch. There will be listeners, fascinated by what they have heard on the airband of the domestic radio and have gone on to a fully-fledged scanner.
They may have something that is bothering them. The Tower gives them clearance for take off, sees them safely into the wild blue yonder then we never hear from them again. Don't worry, Chalkie old bean. Our aircraft never die, they simply go trans-oceanic.
Aeronautical HF Bands
10005 - 10100kHz
11175 - 11400kHz
13200 - 13360kHz
15010 - 15100kHz
17900 - 18030kHz
21870 - 22000kHz
23200 - 23350kHz
2850 - 3155kHz
3400 - 3500kHz
4650 - 4750kHz
5480 - 5730kHz
6525 - 6765kHz
8815 - 9040kHz
Going Transoceanic
As the VHF radio only provides a local service, they use HF on the long haul Stateside. Having come under control of its nearest ATC (Air Traffic Control), the aircraft sets its heading and calls the ACC (Area Control Centre) before requesting trans-oceanic clearance via the OACC (Oceanic Area Control Centre) on HF. We shall deal only with this HF traffic, but for completeness the full chain of command on radio follows this pattern:
Obtain take-off permission from the Tower and local weather conditions either from the Tower or regional Volmet on VHF.
Establish flight level and heading on leaving our airspace on VHF.
Establish contact with nearest Area Control Centre on HF.
On leaving range of Area Control Centre, establish contact with Oceanic Area Control Centre on HF.
Request trans-oceanic clearance.
Establish contact with nearest Area Control Centre in your country of destination.
Establish contact with recognized air lanes over that country via local ATC on VHF
Establish contact with airport tower on VHF.
Request landing clearance and put down on allocated runway.
The chosen runway and terminal building are always the farthest from the car and space did not allow us to document the six hour delay due to the wrong kind of snow at Kennedy in our idealized scheme of things.
Aircraft don't fly high enough to avoid the effects of the ionosphere, so provision is made at 3, 5, 8 and 13Mhz to allow for the daily changes in reception and the longer term seasonal changes.
Our most audible OACC in the UK is at Shannon in Southern Eire in the south and Prestwick in the north. Signing as Shanwick, the 5 and 8Mhz transmissions listed below are a good starting point during daylight conditions.
5450kHz
RAF Volmet from West Drayton, the RAF Weather Service. VOLMET has its root in French. Literally, an inversion of meteo en vol and appears officially as Meteorological Information for Aircraft in Flight.
These are read by a talking computer around the clock throughout the year. Listeners were shocked when a female voice took over but we comms folk knew the slightly higher voice pitch sits nicely in the middle of a USB audio pass-band. Announcing maximum visibility one night, we were half expecting Moonlight can be cruelly deceptive, Amanda...
| Visibility Status | Colour | 3 Octa Cloudbase |
|---|---|---|
| 8Km | Blue | 2500 feet |
| 5Km | White | 1500 feet |
| 3.7Km | Green | 700 feet |
| 1.8Km | Yellow | 300 feet |
| 0.9Km | Amber | 200 feet |
| Less than 0.9Km | Red | Below 200 feet |
| Hazard! | Black |
This Is Shannon Volmet
Shannon Volmet is a weather service. Regular listening will show a fixed pattern to these broadcasts. Temperature, dewpoint - the temperature at which water vapour condenses back to water - wind speed and direction are followed by QNH. This is the ground setting for the altimeter.
Cloud cover at fixed flight levels are given in octas. Consider, if you will, the pilot's field of vision to be from the centre of a large cake split into eight slices. Then three octa would be three-eighths cloud cover at that height.
Stable weather conditions will be reported as No-Sig at the end of the bulletin. This is short for No Significant Change.
The catchy heading of Information in Plain Language Concerning Certain Meteorological Phenomena or SIGMET is usually given in a single word, Snow, Rain, Sleet, a plague of boils or what have you. Some frequencies:
| Frequency | Station |
|---|---|
| 5505kHz | Shannon Volmet |
| 5598kHz | Shannon ATC. Secondary calling on 8906 |
| 5616kHz | Shannon ATC. Secondary calling on 8864 |
| 5649kHz | Shannon ATC. Secondary calling on 8879 |
| 5658kHz | Shannon ATC |
| 5680kHz | Kinloss Rescue |
| 6622kHz | Shannon Volmet and Gander |