Some information about the instrument approach procedure.

instrument approach procedure

Some information about the instrument approach procedure.

a) Segments Of The Instrument Approach Procedure

An instrument approach procedure, according to what ICAO says about it, is made of five segments: arrival, initial segment, intermediate, final and missed.
If any of the standard instrument approach procedure's segments is missing there are some other procedures that can be made on a fix. These alternative procedures are "the reversal procedure" and "the racetrack procedure".
Usually the arrival segment coincides with the final part of a STAR and it ends on IAF (Initial App Fix). The initial segment is between the IAF and the IF (Intermediate Fix). The intermediate segment is between the IF and the FAF (Final App Fix). The final segment, in which the airplane is prepared for landing, is between the FAF and the MAP (Missed App Point).

b) Reversal And Racetrack Procedures

The reversal procedure can be of two types: procedure turn or base turn. The procedure turn can be made with turns first of 45 degrees and then 180 degrees or with turns first of 80 degrees and then 260 degrees. The base turn is made proceeding from fix for 1, 2 or 3 minutes (depending on the category of the airplane) and then making a turn in order to position the aircraft on the in-bound part.

The racetrack procedure is made on a "cookie circuit", with entrance sectors same like those of holding circuits. Usually this procedure is used when the airplanes coming from different directions don't have a segment long enough to allow them the necessary descent to intercept the glide slope.

c) Non Precision Instrument Approach Procedure

The most important component of a non precision instrument approach can be found in the final segment - the MDA/H (Minimum Descent Altitude/Height) - and guarantees the separation from ground obstacles. The MDA/H is the lowest allowed altitude/height at which, once is reached, the pilot will have to maintain until reaching MAP, where if he won't have visual contact will have to go around.

d) Precision Instrument Approach Procedure

In a precision instrument approach procedure the component which is particulary important is the DH (Decision Height), height at which the pilot, once is reached, will have to decide wether to land or to initialize the missed approach procedure, in case he has no visual contact.
The decision height is decided by the airline for each aircraft category in its fleet and it must be above the OCH (Obstacle Clearance Height). The DH coincides with the MAP.

e) Missed Approach Procedure

This procedure is used when the pilot once reached the MAP or the decision height has no visual contact or when there's another airplane on the runway in use. Usually, for the missed approach procedures, the standard climb gradient is 2.5%.
Missed approach procedures, the way that are shown on charts, guarantee the separation from ground obstacles.
This procedure consists of three phases: initial phase, intermediate phase and final phase. The initial phase begins at MAP and it ends when the climbing is stabilized; it follows the intermediate phase which it ends when the aircraft is separated by at least 50 meters from the highest ground obstacle; it follows the final phase which it ends at a FIX, VOR or NDB.

By Claudio Adriano Dobre, © 2005

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