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alternate is required, an airport
can be used if the ceiling is at
least 200 feet above the minimum for the approach to be
flown and visibility is at least 1
SM, but never less than the minimum required for the approach
to be flown. If no instrument
approach procedure has been
published for the alternate airport, the ceiling and visibility
minima are those allowing
descent from the MEA,
approach, and landing under
basic VFR.
PART 135 OPERATORS
Part 135 operators are not
required to file an alternate if, for
at least 1 hour before and 1 hour
after the ETA, the ceiling will be
at least 1,500 feet above the lowest circling approach minimum
descent altitude (MDA). If a circling instrument approach is not
authorized for the airport, the
ceiling must be at least 1,500
feet above the lowest published
minimum or 2,000 feet above
the airport elevation, whichever
is higher. For the instrument
approach procedure to be used at
the destination airport, the forecasted visibility for that airport
must be at least 3 SM, or 2 SM
more than the lowest applicable
visibility minimums, whichever
is greater.
Alternate landing minimums for flights conducted
under Part 135 are described in the OpsSpecs for that
operation. All helicopters operated under IFR must
carry enough fuel to fly to the intended destination, fly
from that airport to the filed alternate, if required, and
continue for 30 minutes at normal cruising speed.
Flight visibility
Not applicable
3 SM
3 SM
3 SM
3 SM
5 SM
None
None
1 SM
3 SM
5 SM
None
None
Distance from clouds
Not Applicable.
Clear of Clouds.
500 feet below.
1,000 feet above.
2,000 feet horizontal.
500 feet below.
1,000 feet above.
2,000 feet horizontal.
500 feet below.
1,000 feet above.
2,000 feet horizontal.
1,000 feet below.
1,000 feet above.
1 statute mile horizontal.
Clear of clouds.
Clear of clouds.
500 feet below.
1,000 feet above.
2,000 feet horizontal.
500 feet below.
1,000 feet above.
2,000 feet horizontal.
1,000 feet below.
1,000 feet above.
1 statute mile horizontal.
Clear of clouds.
Clear of clouds.
Airspace
Class A
Class B
Class C
Class D
Class E:
Less than 10,000 feet MSL
At or above 10,000 feet MSL
Class G:
1,200 feet or less above the surface
(regardless of MSL altitude).
Day, except as provided
in §91.155(b)
Night, except as provided
in §91.155(b)
More than 1,200 feet above
the surface but less
than 10,000 feet MSL
Day
Night
More than 1,200 feet above the
surface and at or above 10,000
feet MSL
B, C, D, E Surface Area Airspace
SVFR Minimums
Day
Night
Helicopter VFR Minimums
Figure 7-7. Helicopter VFR Minimums.
7-9
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 PROCE-
DURES 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]
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
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Instrument Procedures Handbook (IPH)仪表程序手册上(159)
