Cliffnemo
QGHs
Here is what I wrote earlier about this approach procedure:
QGH
As a RAF VHF/DF Operator for over eight years in the 1950’s I provided the bearings for many “QGH’s”. In the 1950’s in the RAF a ‘QGH’ was a request made by a pilot for a ‘Controlled Descent Through Cloud’ and the procedure was to home the aircraft to overhead the airfield with ‘Magnetic Bearings to Steer’ (QDMs).
QGHs would be controlled by the air traffic controller, but on a couple of occasions I did it myself, which was probably against all the rules and regulations, but they worked.
Procedure: The pilot would give a ten-second transmission on the RT which would allow the DF operator to swing the DF aerial to find the ‘null’ on the transmission and by depressing the ‘sense’ plate (which put the aerials out of phase) determine that what was being shown on the DF wheel against the cursor was the correct bearing to the aircraft and it was not a reciprocal. When the sense plate was depressed the signal either when up or down, if it went up the bearing was wrong and the reciprocal was indicated, it was then a matter of swinging the aerial 180-degrees to find the ‘null’ again, go ten degrees either side of the ‘null’ point and depress the sense plate again, this time the signal should go down and if it did one had the correct bearing.
The circumference of the DF wheel was marked with two scales. Top scale showed true bearings from the VHF/DF (QTE’s) whilst the lower scale was marked in red and showed the magnetic course to steer to the airfield (QDMs). To home the aircraft to the airfield overhead for a QGH one read off the bearing shown on the bottom scale, passed it to the controller who in turn passed the magnetic course to steer to the airfield to the aircraft. Aircraft RT transmissions were given every minute or so (or less) with the DF operator taking the bearings. When the aircraft reached the overhead the aircraft’s transmissions sounded all mushy; confirmation that the aircraft was overhead was established by depressing the sense plate and if there was no increase or decrease in signal the aircraft was in fact overhead.
Having informed the controller that the aircraft had reached the overhead, the controller told the aircraft to steer an outbound course about fifteen or twenty degrees to the right of the reciprocal of the inbound runway heading and to descend to an agreed height, possibly 1000ft. The outbound track was flown I seem to recall for about two (or perhaps three minutes). At the end of the two minutes the aircraft was asked to do a rate one turn onto the inbound runway heading, which if all had gone well placed him very near the extended runway centre line at 1000ft. On the inbound leg DF bearings were taken which allowed the controller to check that the aircraft was steering the right course inbound. The controller also gave heights to descend to, so perhaps with one minute to fly to the airfield the aircraft would be at about 500ft and descending to the minimal obstacle height. Unless flying in exceptionally poor visibility the aircraft would see the approach lights and land.
This is all culled from methods last practiced by me over fifty years ago, so if there are any inaccuracies, blame it on age, but the principles are as I remember them.
Photos below show a VHF/DF Station, the radio layout and taking a bearing.
To minimize bearing errors VHF/DF Homers were placed as near as possible to the runway, which on most occasions worked well, until some clot doesn't correct for drift on take-off and manages to ruin the VHF/DF as seen below.
The pupil pilot was in a Harvard and with a severe dent in his wing following the collision managed to do a circuit and land safely. Thankfully the duty VHF/DF operator was shocked but unhurt - if the aircraft had been a couple of feet lower when it hit, a major tragedy would have been the outcome.
