Flying back past Wyton yesterday, I heard for the first time a controller giving instructions for a QGH approach (presumably to a UAS student - I could only hear the controller as the student was on UHF).
How many places still offer this type of approach? Is it a dying breed (along with VDF approaches)? I see in the RAF FLIP approach charts that DF approaches (often UDF) are still fairly common at smaller military airfields - and presumably when there is a DF approach you can get a QGH if the controller is willing...?
I don't think there are any pure civilian units still doing QGH's (I accept that Wyton and certain other units are staffed by civvy ATCO's but they operate under quasi-military regs) so no, the fact that there is DF doesnt mean you can get a QGH!! In fact this being the case I believe the CAA have removed refernces to controller interpreted DF let downs from CAP413.
Well they are in that they are both controller interpreted. The major difference is that a controller providing an SRA has you identified on radar and can see your radar return all the way through the approach. A controller providing a QGH may not have this luxury and can only see an indication from where your RT transmission is coming from on a VDF style display. With a guestimate of the varying wind conditions as you descend, plus judicious use of a stopwatch to time the various legs of the procedure, the controller positions the aircraft onto final approach by issuing frequent heading changes. The controller cannot see the aircraft's radar return at any point during the procedure. This is reflected in the comparatively higher minima used and obviously means little info on other traffic can be passed. I used to do them at Netheravon; the places where they are available to civil pilots are fewer in number all the time. Get one in while you can!
PS Tinstaafl it you still operate thru Scatsta come up to the tower and say hello!
Unfortunately this thread has gone right over my head, I was ok with QNH,QFE, and QDM but just about all the acronyms were totally lost on me. So I may, or may not, be interested in what people have said I will only know when I reach a new level of enlightenment.
Brief summary for those who have lost the will to live...
VDF approaches are instrument approaches where the only information available to the pilot is provided by VHF direction finding. (UDF is UHF DF, used by the military.) The pilot transmits so that the controller can tell him his VDF bearing, given as a QDM (magnetic heading to the station). In practice these approaches are very like NDB approaches, except that you can only check your QDM to the station when you ask for it, instead of watching the needle. The rules to fly them are exactly the same (e.g. if you should be inbound on 195 and the QDM is 200, you need to steer into the error, e.g. 210, until the QDM is 195, then allow for drift). When the ac is over the station the reply will be 'no bearing'. The IAF and MAP are usually the VDF overhead.
QGH approaches are controller-interpreted versions of the above, where the controller interprets your changes in QDR (bearing from the station) and passes headings to fly, level changes, &c. Much easier to fly, as the controller does much of the hard work. Again the IAF and MAP will be at the VDF overhead.
Small military airfields with few facilities still offer these: Wyton and Cosford have been mentioned in the UK, and GŁtersloh abroad. Cranfield and Shoreham still publish VDF approaches.
Does any other country use these? I can imagine them being in use in Africa/Far East.
QGH approaches are controller-interpreted versions of the above, where the controller interprets your changes in QDR (bearing from the station) and passes headings to fly,
A small correction (if memory serves). RAF style QGHs (or CDTC - Controlled Descent Through Cloud) were/are? based on Controller interpretation of QDMs (Magnetic Bearing to the Station) and not QDRs. The headings to fly were passed as 'Steers', and took into account forecast winds aloft.
Possible variations, depending on Aircraft/Station equipment:-
i) QGH to Visual ii) QGH to SRA (Surveillance Radar Approach) iii) QGH to PAR (Precision Approach Radar) v) QGH to ILS.
The advantage of items (i) to (iii) is that all the aircraft requires is a serviceable radio - many military aircraft in the past had little else in the way of aids to navigation.
Pilots could also select a number of other options:-
a) No Compass/No Gyro QGH b) Flame-Out QGH (See BEag's post) c) Speechless QGH (microphone failure) - by Transmitting Carrier Wave Only d) Any Combination of the above!
In the days when QGHs were a very common method of recovering military aircraft, the RAF CADF/CRDF* displays were set by default to QDM. A spring loaded switch could be used to select QTE (True Bearing).
That was all a long time ago, and today you may well be right.
(* Commutated Antenna Direction Finder/Cathode Ray Direction Finder)