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Some information about the instrument approach procedure. |
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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.
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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.
Written by Claudio Adriano Dobre, © 2005
Please notice that this article was written in 2005, so the contained information may be outdated.
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