Control of Aircraft — Page 333, Lesson 437

Right, let's get into the meat of radar vectoring and radar approaches. We've covered the basics of radar control, so now we're looking at the precise, procedural side of it. First, let's talk about ILS vectoring requirements. This is where the controller uses radar to steer you onto the ILS. The key number here is the closing heading. When the whole point of the vectoring is to get you to a point where you'll capture the localizer, the closing heading to the centre line of the ILS localizer is 45 degrees. That's the standard angle. But there's a critical limitation: if parallel runway operations are in use, specifically Modes 1 or 2, that angle is limited to 30 degrees. And you must maintain that closing heading for a distance of not less than 1 nautical mile. So remember the standard is 45 degrees, reduced to 30 for parallel runway Modes 1 or 2, and you hold that heading for at least a mile. Now, let's move to the radar controlled approach. Radar can be used to provide two types of approach: a precision approach, which is a PAR, and a non-precision approach, which is an SRA. In both cases, the radar controller passes radar-derived information to you, the pilot, to permit the aircraft to be flown along a predefined track. The difference is that in the case of PAR, there's also a defined glide path. For SRA, there's no precision glide path; instead, a recommended vertical profile, which is called a virtual glide path, is published. There's a critical failure condition here: if radar contact is lost for any significant period during the last 2 nautical miles of a radar approach, the pilot will be advised to carry out a missed approach procedure. So that's the safety net. Let's drill into the PAR itself. PAR stands for Precision Approach Radar. This is specifically engineered radar equipment that provides very accurate, or precision, azimuth and glide path information to a dedicated radar controller. The key word is "dedicated." While providing a PAR service, the controller is engaged in providing the service to one aircraft only, and will not have any other duty. So it's a one-on-one, full-attention service. The pilot will be passed two types of information. First, azimuth information, which is given as right or left turn or heading instructions. Second, elevation information, which is given as 'on', 'above', or 'below' the glide path. This lets you fly the aircraft along the predetermined flight path. The service continues until the aircraft reaches DH, which is decision height. You, the pilot, would have passed your DH to the ATCO, the air traffic control officer, at the beginning of the procedure. At DH, the pilot will be informed that the aircraft is at DH, and the radar service is terminated. Now, here's a crucial operational point. Because the information is passed in the form of a continuous talk-down, the pilot must stay on the PAR approach frequency. That's non-negotiable. And because the controller is doing the talk-down, the radar controller is therefore responsible for obtaining a landing clearance from the aerodrome controller. Normally, this is done at 4 nautical miles from the threshold of the landing runway, but it may be delayed by the aerodrome controller until 2 nautical miles. And here's the automatic action: if no clearance has been received at 2 nautical miles, the pilot will automatically begin the missed approach procedure. You don't wait for further instruction; you go around. There are also two procedural checks during the approach. At some time during the approach, usually at 3 nautical miles, the pilot will be asked to confirm a final check of the landing gear. And at a military aerodrome, you'll also confirm the flap configuration. Additionally, at some point during the approach, the flight crew will cross-check the position of the aircraft against the PAR information, for instance using DME, which is distance measuring equipment, and rad alt information, which is radio altimeter information. Finally, a note on where you'll find this equipment. PAR will not generally be found at civilian aerodromes. However, the new generation of PAR equipment is widely installed at military aerodromes. So this is a procedure you're far more likely to encounter in a military environment.