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
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
Read on : Instrument
Approach Procedures: part 2