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  Thursday 29 June 2017 09:03 GMT  

Aviation Theory

Instrument Approach Procedures part 1

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INTRODUCTION

The Instrument Approach Procedure (IAP) Charts, also often referred to as approach plates, portray the aeronautical data which is required to execute instrument approaches to airports. Each chart depicts the IAP, all related navigation data, communications information, and an airport sketch. Each procedure is designated for use with a specific electronic navigational aid, such as ILS, VOR, NDB, RNAV, etc. Airport Diagram Charts, where published, are included.

THE SEGMENTS OF AN INSTRUMENT APPROACH

The instrument approach can be divided into five separate segments which blend to form one complete approach:

1. Arrival segment or feeder route
2. Initial approach segment
3. Intermediate approach segment
4. Final approach segment
5. Missed approach segment

THE ARRIVAL SEGMENT

The feeder route is the route taken from the enroute phase of the light to the initial approach fix (IAF). Normally it starts at an enroute fix and ends at the IAF. The IAF is usually the first navigational facility associated with the actual approach. The IAP will show the feeder route, or routes, minimum altitudes, course to be flown and the distance to the IAF.

In some instances, the IAF is part of the enroute structure and there is no feeder route. There may also be several feeder routes to accommodate flights from different directions leading to the same IAF.

INITIAL APPROACH SEGMENT

During the initial approach segment, the aircraft is maneuvered to enter the intermediate section, which will align it, approximately, with the final approach course. This segment commences at the IAF and may consist of a course, radial, DME arc, procedure turn, holding pattern, radar vector, or a combination of one or more of these procedures.

INTERMEDIATE APPROACH SEGMENT

During this segment, the aircraft should be prepared for the final approach. Speed adjustments and positioning should be completed at this time. Prelanding checks are also normally done during the intermediate segment.

The intermediate segment ends at the final approach fix (FAF). The FAF may be an NDB, LOM, a procedure turn, or a reversal turn in a holding pattern.

FINAL APPROACH SEGMENT

The final approach segment for a nonprecision approach begins at the FAF and ends at the missed approach point (MAP). In some approaches, the FAF and IAF may be the same point. For example, the LOM may be the IAF flying outbound and may also be the FAF when inbound.

For nonprecision approaches, the final approach may be made for a straight-in landing or it may be to a circling approach. Which it is depends on the alignment of the final approach and the runway.

The final approach segment for a precision approach starts at the final approach point (FAP). This point is where the intermediate approach segment intersects the glidepath for the precision portion of the approach. ILS approaches are designed such that the glideslope will be intercepted from below. This prevents the pilot from inadvertently intercepting one of the false glideslopes which may exist above the actual glideslope.

A fix, such as an outer marker (OM), DME distance or radar fix, exists to allow you to check the glidepath/altitude relationship before commencing your descent. Timing also commences at the FAF to assist in identifying the MAP on some nonprecision approaches.

Descent below the minimum permitted altitude should not occur unless you have visual contact with the runway environment, such as approach lights, runway lights, etc. (listed is FAR 91.175).

MISSED APPROACH SEGMENT

If you are not visual upon reaching a particular point or minimum altitude, then a missed approach must be made.

The MAP for a precision approach is defined as the intersection of the glideslope and the decision height (DH) and is not shown on the IAP. Unless the pilot is visual, a missed approach should be commenced immediately upon reaching the DH.

The MAP for a nonprecision approach is defined by a fix, a facility, or by timing. The MAP is indicated on the plan and profile diagrams as a dotted line. There is also a text description. If a turn is called for in the missed approach procedure, it should not be made before passing the MAP, unless authorized by ATC.

During the nonprecision approach, the pilot may not descend below the minimum descent altitude (MDA) unless visual. Once reaching the MDA, the pilot may continue to track inbound until reaching the MAP.

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Read on : Instrument Approach Procedures: part 2
 

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