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Instrument Flying Handbook
Navigation Systems
Advanced Technologies

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Instrument Flying


Table of Contents

Chapter 1. Human Factors
Chapter 2. Aerodynamic Factors
Chapter 3. Flight Instruments
Chapter 4. Section I
Airplane Attitude Instrument
Using Analog Instrumentation
Chapter 4. Section II
Airplane Attitude Instrument
Using an Electronic Flight

Chapter 5. Section I
Airplane Basic
Flight Maneuvers
Using Analog Instrumentation
Chapter 5. Section II
Airplane Basic
Flight Maneuvers
Using an Electronic Flight

Chapter 6. Helicopter
Attitude Instrument Flying

Chapter 7. Navigation Systems
Chapter 8. The National
Airspace System

Chapter 9. The Air Traffic
Control System

Chapter 10. IFR Flight
Chapter 11. Emergency

GPS approaches are requested and approved by ATC using
the GPS title, such as "GPS RWY 24" or "RNAV RWY 35."
Using the manufacturer's recommended procedures, the
desired approach and the appropriate IAF are selected from
the GPS receiver database. Pilots should fly the full approach
from an initial approach waypoint (IAWP) or feeder fix unless
specifically cleared otherwise. Randomly joining an approach
at an intermediate fix does not ensure terrain clearance.

When an approach has been loaded in the flight plan, GPS
receivers will give an "arm" annunciation 30 NM straight
line distance from the airport/heliport reference point. The
approach mode should he "armed" when within 30 NM
distance so the receiver will change from en route CDI
(±5 NM) and RAIM (±2 NM) sensitivity to ± 1 NM terminal
sensitivity. Where the IAWP is within 30 NM, a CDI
sensitivity change will occur once the approach mode is
aimed and the aircraft is within 30 NM. Where the IAWP
is beyond the 30 NM point, CDI sensitivity will not change
until the aircraft is within 30 NM even if the approach is
armed earlier. Feeder route obstacle clearance is predicated
on the receiver CDI and RAIM being in terminal CDI
sensitivity within 30 NM of the airport/heliport reference
point therefore, the receiver should always he armed. no later
than the 30 NM annunciation.

Pilots should pay particular attention to the exact operation
of their GPS receivers for performing holding patterns and in
the ease of overlay approaches, operations such as procedure
turns. These procedures may require manual intervention
by the pilot to stop the sequencing of WPs by the receiver
and to resume automatic GPS navigation sequencing once
the maneuver is complete. The same WP may appear in the
route of flight more than once and consecutively (e.g., IAWP,
final approach waypoint (FAWP), missed approach waypoint
(MAWP) on a procedure turn). Care must be exercised to
ensure the receiver is sequenced to the appropriate WP for
the segment of the procedure being flown, especially if one
or more fly-over WPs are skipped (e.g., FAWP rather than
IAWP if the procedure turn is not flown). The pilot may need
to sequence past one or more fly-over of the same WP in
order to start GPS automatic sequencing at the proper place
in the sequence of WPs.

When receiving vectors to final, most receiver operating
manuals suggest placing the receiver in the non sequencing
mode on the FAWP and manually setting the course. This
provides an extended final approach course in cases where
the aircraft is vectored onto the final approach course outside
of any existing segment which is aligned with the runway.
Assigned altitudes must he maintained until established on a
published segment of the approach. Required altitudes at WPs
outside the FAWP or step-down fixes must he considered.

Calculating the distance to the FAWP may he required in
order to descend at the proper location.

When within 2 NM. of the FAWP with the approach mode
armed, the approach mode will switch to active, which results
in RAIM and CDI sensitivity changing to the approach
mode. Beginning 2 NM prior to the FAWP, the full scale
CDI sensitivity will change smoothly from ±1 NM to ±0.3
NM at the FAWP. As sensitivity changes from ± 1 NM to
±0.3 NM approaching the FAWP, and the CDI not centered,
the corresponding increase in CDI displacement may give
the impression the aircraft is moving further away from the
intended course even though it is on an acceptable intercept
heading. If digital track displacement intonation (cross-track
error) is available in the approach mode, it may help the pilot
remain position oriented in this situation. Being established
on the final approach course prior to the beginning of the
sensitivity change at 2 NM will help prevent problems in
interpreting the CDI display during ramp-down. Requesting
or accepting vectors, which will cause the aircraft to intercept
the final approach course within 2 NM of the FAWP, is not

Incorrect inputs into the GPS receiver are especially critical
during approaches. In some cases, an incorrect entry can
cause the receiver to leave the approach mode. Overriding
an automatically selected sensitivity during an approach
will cancel the approach mode annunciation. If the approach
mode is not armed by 2 NM prior to the FAWP, the approach
mode will not become active at 2 NM prior to the FAWP and
the equipment will flag. In these conditions, the RAIM and
CDI sensitivity will not ramp down, and the pilot should not
descend to minimum descent altitude (MDA), hot fly to the
MAWP and execute a missed approach. The approach active
annunciator and/or the receiver should he checked to ensure
the approach mode is active prior to the MAWP.

A GPS missed approach requires pilot action to sequence the
receiver past the MAWP to the missed approach portion of
the procedure. The pilot must be thoroughly familiar with
the activation procedure for the particular GPS receiver
installed in the aircraft and must initiate appropriate action
after the MAWP. Activating the missed approach prior to the
MAWP will cause CDI sensitivity to change immediately to
terminal (± 1 NM) sensitivity, and the receiver will continue
to navigate to the MAWP. The receiver will not sequence past
the MAWP. Turns should not begin prior to the MAWP. If
the missed approach is not activated, the GPS receiver will
display an extension of the inbound final approach course and.
the along track distance (ATD) will increase from the MAWP
until it. is manually sequenced after crossing the MAWP.