Approach Procedures — Page 179, Lesson 254

I want to walk you through the approach procedures now — this is where the aircraft leaves the en-route system and gets lined up for the runway. We'll go segment by segment, because each one has its own start point, end point, and minimum obstacle clearance. Let's start with the arrival segment. This is the very first part. It begins at the moment the aircraft departs from the en-route airways system to begin the instrument arrival. That departure point will normally be a radio navigation facility. Here's the key rule: if that facility is 25 NM or more from the aerodrome, then a standard arrival route — a STAR — will be specified. The STAR plate shows the arrival routes for London Heathrow from the northwest, via the Ockham VOR, which is the OCK VOR. If the distance is less than 25 NM, then the aircraft routes directly from the point of leaving the airway to the facility that serves as the IAF — the initial approach fix — for the procedure. In either case, the en-route MOC is applied. MOC is minimum obstacle clearance — the minimum vertical clearance you must maintain above obstacles. And the altitude specified for the aircraft to be over the IAF is not below the highest MSA for the aerodrome — that's the minimum sector altitude. It's usual for aircraft to be radar vectored from a convenient point onto the final approach track. Now the initial segment. This is where the aircraft is directed to a point at which the intermediate segment can be intercepted. It starts at the IAF and ends at the IF — the intermediate fix. Aircraft speed and configuration depend on distance from the aerodrome and any need for descent. The MOC in the initial segment is 300 m, which is 984 ft. Track guidance is normally provided with a maximum intercept angle to the IF of 90° for a precision approach and 120° for a non-precision approach. Now, if track guidance to the IF is not available, a DR segment may be specified — that's dead reckoning. For the DR segment, the interception angle to the intermediate segment track must be no greater than 45°, and the length of the DR track no more than 10 NM. And where a straight-in approach is not feasible, or there's no suitable remote IAF or IF, then a track reversal, racetrack, or holding pattern is required. Next, the intermediate segment. This is the segment in which the aircraft's speed and configuration are adjusted to prepare for the final approach. Descent in this segment is kept to a minimum. It starts at the IF and ends at the FAF — the final approach fix. If no FAF exists, it ends when the aircraft is established on the final inbound track. The MOC in the intermediate segment reduces from 300 m at the IF to 150 m at the end of the segment. Finally, the final segment. Its beginning depends on the type of approach and the availability of a suitable FAF. In this segment, the aircraft is finally configured, alignment with the runway takes place, and descent for landing is commenced. So the whole picture: arrival segment gets you from the airway to the IAF, initial segment gets you from the IAF to the IF, intermediate segment gets you from the IF to the FAF, and the final segment takes you from the FAF down to the runway. Each one has its own MOC — 300 m in the initial, reducing from 300 to 150 m in the intermediate — and its own intercept angle limits. That's the skeleton of every instrument approach you'll fly.