Approach Procedures — Page 175, Lesson 252

Let’s start with the big picture. An approach procedure is not one single manoeuvre — it’s built from five distinct parts, and we call them procedure segments. I want you to hold that word, segment, because everything in this chapter hangs off it. The five segments are: the Arrival Segment, sometimes called the Arrival Route; the Initial Segment; the Intermediate Segment; the Final Segment; and finally the Missed Approach Segment, together with its Missed Approach Procedure. I’ll be covering each one in detail later in the chapter, but for now, just get the skeleton: arrival, initial, intermediate, final, and missed approach. Now, the next idea is the straight-in approach. Wherever the terrain and the airspace allow, the procedure designer will specify a straight-in approach. What that means is that each of those five segments is aligned with the extended runway centre line — the whole procedure is laid out along the line of the runway, extended out beyond the threshold. But there’s an important exception. A non-precision approach may specify the final approach track converging to the runway heading at an angle of 30° or less. So even in a straight-in procedure, the final track doesn’t have to be exactly on the centre line — it can converge toward the runway heading, as long as that convergence angle is 30 degrees or less. Here’s a critical operational point. All these procedures depict still air tracks. That means the tracks drawn on the chart assume zero wind. So you, as the pilot, are required to make allowance for the wind in order to make good the specified track. The chart gives you the track to fly; you have to correct for drift to stay on it. Now, if terrain or other restrictions preclude a straight-in approach — in other words, if you can’t line up with the runway — then a circling approach will be specified instead. And there’s a third option: an aircraft may be offered an omni-directional or sector arrival by ATC, when appropriate, and taking into consideration the MSA — that’s the Minimum Safety Altitude. So you have three possibilities: straight-in, circling, or an omni-directional/sector arrival offered by ATC. One more precise definition here, and it’s a classic exam point. The definition of being established on an NDB — that’s a Non-Directional Beacon — is to be within 5° either side of the final approach track. So you’re not “established” the moment you cross the beacon; you’re established when you’re inside a 5-degree band on either side of the final approach track. Now let’s look at the physical characteristics of the segments. Take the vertical cross section of any segment. It’s divided into two types of areas: primary and secondary MOC areas. MOC stands for Minimum Obstacle Clearance. Full obstacle clearance is applied over the primary area, and that clearance reduces to zero at the outer edges of the secondary areas. So the primary area gets the full protection, and as you move out through the secondary area toward its outer edge, the obstacle clearance tapers down to nothing. I’ve got a figure for you that shows exactly this — the characteristics of the segments, with the primary and secondary areas and how the clearance behaves. Take a look at it. So to tie it together: five segments, straight-in as the preferred design with that 30-degree convergence allowance for non-precision, still air tracks with the pilot correcting for wind, circling or omni-directional arrivals as alternatives, the 5-degree NDB established criterion, and the primary/secondary MOC structure with full clearance over primary tapering to zero at the outer edges of secondary. That’s the foundation for the whole approach procedure.