Ref my post #6 above.
Following from my training notes.
Direction Finding (DF)
The aeronautical stations that offer a VHF Direction Finding (VDF) service are listed in the UK AIP AD. Some VDF stations stipulate that the service is not available for enroute navigation purposes (except in emergency). VDF bearing information will only be given when conditions are satisfactory and radio bearings fall within calibrated limits of the station. If the provision of a radio bearing is not possible the pilot will be told of the reason.
A pilot may request a bearing or heading using the appropriate phrase or Q code to specify the service required. Each aircraft transmission shall be ended by the aircraft call sign.
A VDF station will provide the following as requested:
1. QDR – Magnetic bearing of the aircraft from the station (i.e. ..... Approach G-ABCD request QDR G-ABCD).
2. QDM – Magnetic heading to be steered by the aircraft (assuming no wind) to reach the VDF station (i.e. ..... Approach G-ABCD request QDM G-ABCD).
3. QTE – True bearing of the aircraft from the station (i.e. ..... Approach G-ABCD request True Bearing (or QTE) G-ABCD).
The direction-finding station will reply in the following manner:
1. The appropriate phrase or Q code.
2. The bearing or heading in degrees in relation to the direction finding station.
3. The class of bearing.
4. The time of observation, if necessary.
The accuracy of the observation is classified as follows:
• Class A – Accurate within plus or minus 2 degrees
• Class B – Accurate within plus or minus 5 degrees
• Class C – Accurate within plus or minus 10 degrees
• Class D – Accuracy less than Class C
NOTE: Normally no better than Class B bearing will be available.
QGH (Controlled Descent Through Cloud) Procedure
QGH letdowns may be provided, when requested by a pilot, at aerodromes where the procedure is approved. The procedure provides for control of an aircraft from its initial approach level to a position, from which an approach can be completed visually, approach may not be aligned with a runway.
On receiving a request for a QGH the aircraft is to be homed overhead the VDF aerial at or descending to the lowest available flight level/altitude taking into account the minimum safe flight level or safety altitude as appropriate. During homing the following message will be passed to the pilot:
During the procedure aircraft replies are used to obtain D/F bearings. Pilots may be asked to make additional transmissions for D/F. With some equipment the full callsign is sufficient to obtain bearings.
Two D/F indications are required to confirm the aircraft is overhead the VDF aerial; then instructions are given to achieve the desired outbound track.
On completion of the overhead turn and when bearings indicate the aircraft is outbound the controller starts timing the outbound leg and provides heading corrections derived from a series of bearings to make good the desired outbound track. Descent instructions and the appropriate pressure setting are also given during this procedure.
On completion of the timed outbound leg (e.g. 3 min) the aircraft is instructed to turn onto a heading to achieve the final approach track.
When the aircraft reports steady on completion of the inbound turn, headings will continue to be given to achieve the inbound track. During the inbound leg the controller will pass instructions to be followed in the event of a missed approach (Note: At military airfields the weather and missed approach procedure may be passed at an earlier stage in the procedure). Descent clearance to minimum descent height and the QFE will be given on this leg.
If the pilot has not reported ‘visual’ by the time minimum descent height is reached he may be instructed to maintain level flight until he is overhead the VDF. If the aircraft is not ‘visual’ when overhead the VDF, the controller will give the instruction to carry out a missed approach procedure.
The following appeared in "BUKA" the RAF Thornhill station magazine in 1952:
BUKA December, 1952
THORNHILL HOMER
By L.A.C. J. VINE
Thornhill has its own legion of “forgotten men,” so it would appear. A frustrated band of individuals, forsaken and abandoned—hibernating on the extremities of the airfield.
Few people know they exist, but these “few” realise only too well the loneliness of braving the elements of a winter’s night, or the humidity of being cooped up on a summer’s evening.
The forsaken men—six R/T. D/F. Operators, The place—the camp’s Homer Station, one mile from Air Traffic Control on the far side of the main runway.
From early morn until late at night these isolated beings keep up a continuous watch Their function to pass directional bearings requested by aircraft enabling pilots to pin-point their positions: and in cases of distress to bring them home safely.
Last year the total number of bearings passed by these operators was 35,903, and an RAF record of 2,810 bearings in ten days, was set up. A place of prominence is given to a commendation from the last Signals Officer on this fine standard.
A conical shaped, black and white chequered hut, with what seems to be two television masts poking through the roof, is how the Homer appears to the layman. Recently the building was uprooted and moved even farther away from civilisation. But inside a far from melancholy air prevails, and many an amusing incident helps to break the monotony of the day.
WILD LIFE
All kinds of rodents, lizards and bees pester the life of the occupants. Some months ago, by chance, a swarm of bees settled around the aerial platform of the Homer roof, on the old site. During a particularly hot day the swarm descended into the building and the “ship” was quickly abandoned with sorely-stung airmen springing in all directions. Fire Section beekeeper F./Sgt. Dare was hurriedly called in to exorcise the pests so work could continue.
Another story of woe told me, happened during the summer. A very perspiring operator decided to strip down to the waist, and with his feet firmly positioned on the table, a cloud of smoke circling about his head, he settled down with a derogatory magazine at band. Minutes later, the Group Signals Officer’s head appeared around the door—even now the airman’s face glows red each time the door is flung open.
But the job of manning the Homer is done well and efficiently. Thornhill being a master diversion airfield in this part of Rhodesia, civilian aircraft use our Homer facility quite extensively. Twice a week the BOAC Comet gives a call, on its run between Johannesburg and Livingstone.
OPERATOR BITES THE DUST
Before the recent upheaval the “ancient” Homer’s position was in close proximity to the airfield’s main runway. Planes frequently barely scraped over the aerials, and a wave from pilot to operator was always good to boost trembling morale, at those times. However, the standing leg-pull is the thy one mistrusting operator leapt for his life through the observation hatchway on seeing an Anson, due to wind-drift, heading straight for the building.
Tall, fair wavy haired Cpl. Dave Pearce keeps an eye on the proceedings, but the staff of “big-dip” operators is “Stinkie” Hill, “Arny” Arnold, “Dad” Stephens, “Prof” Hawes, and the latest arrival, “Ginger” Burgoyne.
So, if you’re ever that far off course, drop in and witness these “gen” boys working their fine array of technical equipment.