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operate at a higher landing weight into a field that
has restrictive obstacles in the missed approach or
rejected landing climb path. On these occasions, the
full-flap landing speed may not allow the airplane
enough energy to successfully complete a go-around
and avoid any high terrain that might exist on the
climb out. Therefore, all-engine and engine-out
missed approaches, as well as rejected landings,
must be taken into consideration in compliance with
the regulations. [Figure 5-2]
Flaps 30° Approach
Flaps 17° Approach
Climb Performance not Adequate
for Terrain
Missed approach with full landing flaps,
lowest approach speed, but poor
performance in missed approach climb.
Missed approach with lower flap setting,
higher approach speed, and improved
climb performance.
Figure 5-2. Reduced Flap Settings Effect on Go-Around.
5-7
APPROACH SPEED AND CATEGORY
Two other critical performance factors that should be
considered during the planning phase of an instrument
approach are aircraft approach category and planned
approach speed. According to the December 26, 2002
amendment of Part 97.3 (b), aircraft approach category means a grouping of aircraft based on reference
landing speed (V REF ), if specified, or if V REF is not
specified, 1.3 V S0 (the stalling speed or minimum
steady flight speed in the landing configuration) at the
maximum certificated landing weight. V REF refers to
the speed used in establishing the approved landing distance under the airworthiness regulations constituting
the type certification basis of the airplane, regardless of
whether that speed for a particular airplane is 1.3 V SO ,
1.23 V SR , or some higher speed required for airplane
controllability such as when operating with a failed
engine. The categories are as follows:
• Category A: Speed less than 91 knots.
• Category B: Speed 91 knots or more but less than
121 knots.
• Category C: Speed 121 knots or more but less
than 141 knots.
• Category D: Speed 141 knots or more but less
than 166 knots.
• Category E: Speed 166 knots or more.
• NOTE: Helicopter pilots may use the Category A
line of minimums provided the helicopter is operated at Category A airspeeds.
An airplane is certified in only one approach category, and
although a faster approach may require higher category
minimums to be used, an airplane cannot be flown to the
minimums of a slower approach category. The certified
approach category is permanent, and independent of the
changing conditions of day-to-day operations. From a
TERPS viewpoint, the importance of a pilot not operating
an airplane at a category line of minimums lower than the
airplane is certified for is primarily the margin of protection provided for containment of the airplane within the
procedure design for a slower airplane. This includes
height loss at the decision altitude, missed approach climb
surface, and turn containment in the missed approach at
the higher category speeds. Pilots are responsible for
determining if a higher approach category applies. If a
faster approach speed is used that places the aircraft in a
higher approach category, the minimums for the appropriate higher category must be used. Emergency returns at
weights in excess of maximum certificated landing
weight, approaches made with inoperative flaps, and
approaches made in icing conditions for some airplanes
are examples of situations that can necessitate the use of a
higher approach category minima.
Circling approaches conducted at faster-than-normal
straight-in approach speeds also require a pilot to consider
the larger circling approach area, since published circling
minimums provide obstacle clearance only within the
appropriate area of protection, and is based on the
approach category speed. [Figure 5-3] The circling
approach area is the obstacle clearance area for airplanes
maneuvering to land on a runway that does not meet the
criteria for a straight-in approach. The size of the circling
area varies with the approach category of the airplane, as
shown in Figure 5-3. A minimum of 300 feet of obstacle
clearance is provided in the circling segment. Pilots
should remain at or above the circling altitude until the
airplane is continuously in a position from which a
descent to a landing on the intended runway can be made
at a normal rate of descent and using normal maneuvers.
Since an approach category can make a difference in the
approach and weather minimums and, in some cases, prohibit flight crews from initiating an approach, the
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Instrument Procedures Handbook (IPH)仪表程序手册上(108)
