HELICOPTER INSTRUMENT APPROACHES
Helicopter instrument flight is relatively new when
compared to airplane instrument flight. Many new helicopter
instrument approach procedures have been
developed to take advantage of advances in both avionics
and helicopter technology.
STANDARD INSTRUMENT APPROACH PROCEDURES
TO AN AIRPORT
Helicopters flying standard instrument approach procedures
(SIAP) must adhere to the MDA or decision altitude
for Category A airplanes, and may apply the Part
97.3(d-1) rule to reduce the airplane Category A visibility
by half but in no case less than 1/4 SM or 1200
RVR [Figure 7-10 on page 7-11]. The approach can be
initiated at any speed up to the highest approach category
authorized; however, the speed on the final
approach segment must be reduced to the Category A
speed of less than 90 KIAS before the MAP in order to
apply the visibility reduction. A constant airspeed is
recommended on the final approach segment to comply
with the stabilized approach concept since a decelerating
approach may make early detection of wind shear
on the approach path more difficult. [Figure 7-8]
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When visibility minimums must be increased for inoperative
components or visual aids, use the Inoperative
Components and Visual Aids Table (provided in the
front cover of the U.S. Terminal Procedures) to derive
the Category A minima before applying any visibility
reduction. The published visibility may be increased
above the standard visibility minima due to penetrations
of the 20:1 and 34:1 final approach obstacle
identification surfaces (OIS). The minimum visibility
required for 34:1 penetrations is 3/4 SM and for 20:1
penetrations 1 SM (see Chapter 5). When there are
penetrations of the final approach OIS, a visibility
credit for approach lighting systems is not allowed for
either airplane or helicopter procedures that would
result in values less than the appropriate 3/4 SM or 1
SM visibility requirement. The Part 97.3 visibility
reduction rule does not apply, and you must take precautions
to avoid any obstacles in the visual segment. Procedures with penetrations of the final approachOIS will be annotated at the next amendment with “Visibility Reduction by Helicopters NA.”
Until all the affected SIAPs have been annotated, an
understanding of how the standard visibilities are
established is the best aid in determining if penetrations
of the final approach OIS exists. Some of the
variables in determining visibilities are: DA/MDA
height above touchdown (HAT), height above airport
(HAA), distance of the facility to the MAP (or the
runway threshold for non-precision approaches), and
approach lighting configurations.
The standard visibility requirement, without any
credit for lights, is 1 SM for nonprecision approaches
and 3/4 SM for precision approaches. This is based on
a Category A airplane 250-320 feet HAT/HAA, and
for nonprecision approaches a distance of 10,000 feet
or less from the facility to the MAP (or runway
threshold). For precision approaches, credit for any
approach light configuration, and for non-precision
approaches (with a 250 HAT) configured with a
MALSR, SSALR, or ALSF-1 normally results in a
published visibility of 1/2 SM.
Consequently, if an ILS is configured with approach
lights or a nonprecision approach is configured with
either MALSR, SSALR, or ALSF-1 lighting configurations
and the procedure has a published visibility of 3/4
SM or greater, a penetration of the final approach OIS
may exist. Also, pilots will be unable to determine
whether there are penetrations of the final approach
OIS if a nonprecision procedure does not have
approach lights, or is configured with ODALS, MALS,
or SSALS/SALS lighting since the minimum published
visibility will be 3/4 SM or greater.
As a rule of thumb, approaches with published visibilities
of 3/4 SM or more should be regarded as having
final approach OIS penetrations and care must be taken
to avoid any obstacles in the visual segment.
Approaches with published visibilities of 1/2 SM or
less are free of OIS penetrations and the visibility
reduction in Part 97.3 is authorized.
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