Technique - Anatomy of an approach

February 5, 2015 By Ian J. Twombly

Making the transition from cruise to landing in instrument conditions

Anatomy of an Approach

To blindly fly in the clouds from a comfortable cruising altitude to just a few hundred feet above the ground can be a surreal experience. The pilot uses a simple radio or satellite signal to guide the aircraft through a series of methodically constructed segments of steps called an instrument approach. The ultimate goal is to be safely guided low enough to get below the clouds to a point at which the runway can be seen and a normal landing can be made. Most approaches can be broken into five distinct segments that flow together seamlessly.

Steps

1. The arrival

The transition between the en route phase and the instrument approach is the arrival or feeder route. It usually is depicted with a specific course, distance, and altitude, although air traffic control can assign alternatives.

2. The initial approach

Most approaches begin at the initial approach fix, which also serves as the starting point of the initial approach segment. This segment often is in line with the extended centerline of the runway.

3. The intermediate approach

This crucial part of the approach is when configuration changes are made, such as lowering flaps and gear. It’s the final chance for the pilot to slow down and get the airplane fully stabilized before the final descent, which begins at the final approach fix.

4. The final approach

If everything goes well, the instrument approach ends at the final approach segment, which takes the pilot from final approach fix to the decision altitude and missed approach point. Typically only a few miles long, the final approach should be a stable descent that brings the airplane to a minimum altitude prior to or at the missed approach point.

5. Missed approach

If the pilot doesn’t see the runway or its surrounding environment by the time he reaches the missed approach point, he is required to fly the missed approach segment. Each approach has a different design, but all missed approach segments, or procedures, call for a climb, and ultimately, they spell out a place to hold so pilots can try the approach again or divert.

Categorically speaking

Instrument approaches are defined by many factors

Instrument approaches are considered either precision or nonprecision. The terms are somewhat misleading because a significant amount of accuracy is necessary to fly close to the ground without an outside visual reference. Yet there are practical considerations for the two classifications. The ILS—or instrument landing system—is the only precision approach most general aviation pilots will ever fly. In most cases it will allow a descent to about 200 feet above the ground (called a decision height), at which point a missed approach must be flown if there are no outside references. Nonprecision approaches can be everything from the get-you-in-the-same-state nondirectional radio beacon (NDB) to the ILS-like LPV (GPS with vertical guidance). These approaches are flown down to a missed approach point, which varies depending on the accuracy of the navigation sources and other factors.