One afternoon I was returning to the airfield at a little below 2000 feet - finding more lift was unlikely as the wave was nearer 3000 feet. I spent ten minutes or so meandering around looking for the odd patch of weak low lift like a fading thermal, but mainly relaxing after the earlier workload and admiring the view.
Passing by the airfield I noticed that the wind had turned again. We had departed on runway 26N (to the west), but the wind was now a south-westerly so we would have to land from the west onto runway 08N or 08S. The wind also suggested a left hand circuit from the north side. As we passed 1300 feet I steered us north-east of the airfield past the point I would start the circuit and carried on a little towards Aboyne.
As we approached the village the instructor told me we should remember that around the middle of Aboyne controlled airspace starts in a block towards the east (the Aberdeen Control Area - Class D Airspace). It is important not to enter controlled airspace without permission. Gliders are so small and non-metallic that they are unlikely to show up on Air Traffic Control (ATC) radar - and routine communication with ATC requires a radio license.
In our case there was no risk of infringement as the base of the controlled airspace starts at 3000 above sea level - about 2,500 feet above the airfield (elevation 460 feet). As we continued to descend slowly I turned back towards the airfield and did a couple of 'S' turns to lose more height, keeping the airfield in sight. When the altimeter reached 800 feet I joined the circuit by turning onto a downwind leg (parallel to but offset from the airfield), slid over the hilltop to the north of the airfield at the standard calm air approach speed of 55 knots, and landed normally.
The sky is divided up into many different types of airspace. It's a fairly complicated set of rules. The following provides a summary:
U.K. airspace up to Flight Level 245 (24,500 feet at standard air pressure) is divided into Flight Information Regions (FIRs). Above the FIRs lie Upper FIRs (UIRs). Within the FIRs & UIRs the airspace is divided into six classifications: A,B,D,E,F,G (ICAO standards). Class C is not used in the U.K. Classes A,B,D,E are controlled airspace.
Each class may contain one or more of the following:
| Airway | Typically 10 nautical miles wide. Permanent IFR applies. Gliders can cross certain airways in VMC. |
| Control Zone (CTR) |
Usually around an airport from ground level to a specified height. A glider cannot enter a Class A CTR (e.g. Heathrow). Other classes may only be entered with ATC clearance. |
| Control Area (CTA) Terminal Manouevering Area (TMA) Terminal Control Area (TMA) |
Similar to CTR but starts at a height above ground level to a specified height. A glider cannot enter a Class A CTA unless a letter of agreement has been obtained. Other Classes permit glider access in VMC with or without ATC clearance. |
The classes are as follows:
| A | All airways. London CTR & TMA, Manchester TMA, Daventry CTA, Worthing CTA, Cotswold CTA |
| B | Upper Airspace Control Area: the London (i.e. England & Wales) and Scottish UIRs between FL245 and FL660. Gliders may enter without clearance and with or without VMC. |
| D | Most other CTRs, CTAs, TMAs including the Aberdeen CTR/CTA and the Scottish TMA above 6000 feet amsl. Gliders may enter in specified Class D airspace subject to VMC. In other Class D airspace ATC clearance may be given or a local arrangement may apply. |
| E | Includes the Scottish TMA below 6000 feet amsl and the Scottish CTR outside the Glasgow/Prestwick CTRs. Gliders may enter without ATC clearance in VMC. |
| F | Uncontrolled airspace. All advisory air routes. Gliders may cross without restriction but care must be taken. |
| G | Uncontrolled airspace. All U.K. airspace not covered by Classes A to F. |
Other definitions:
| VMC | Visual Meteorological Conditions; weather conditions allowing flight under VFR. In Class A,B,D airspace (or Class F above FL100 i.e.10,000 feet) VMC means at least 1500m horizontally and 1000 feet vertically from cloud with visibility 8Km. In Class F below FL100, VMC has the same cloud minima but a visibility of 5Km. |
| VFR | Visual Flight Rules. A pilot is responsible for avoiding collision with other aircraft. |
| IMC | Instrument Meteorological Conditions; weather conditions not permitting VFR, requiring flight under IFR |
| IFR | Instrument Flight Rules. |
A glider must not fly over any congested area below a height which would enable it to land clear of the area, or below 1,500 feet above the highest fixed object within 2,000 feet, whichever is the higher. The height is raised to 3,000 feet for any gathering of more than 1,000 people. Exceptions are hill soaring, takeoff & landing and life-saving.
A flight plan and ATC clearance is required for all IFR flights in controlled airspace and for VFR flights in Class B and D airspace. This need not be construed as the compilation and submission of the Flight Plan Form CA 48/RAF F2919 though in some circumstances, particularly for IFR flights, this could be advantageous. A flight plan is a means of providing sufficient particulars of flight to an ATC Unit to enable that unit to issue an ATC clearance which will permit flight in the particular airspace subject to any instructions contained in the clearance. This requirement will be met by contacting the ATC Unit on the appropriate frequency giving details of the aircraft's position, level and proposed track and requesting clearance to enter the Controlled Airspace.