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Once the determination is made regarding the instrument approach and landing runway you will use, with its
associated descent area, ATC will not permit a change to
another navigational aid that is not aligned with the landing runway. When altitude restrictions are required for
separation purposes, ATC avoids assigning an altitude
below 5,000 above the airport elevation.
There are numerous exceptions to the high performance
airplane arrival procedures previously outlined. For
example, in a nonradar environment, the controller may
clear the flight to use an approach based on a NAVAID
other than the one aligned with the landing runway,
such as a circling approach. In this case, the descent to
a lower altitude usually is limited to the descent area
with the circle-to-land maneuver confined to the traffic
pattern. Also in a nonradar environment, contact
approaches may be approved from 5,000 above the airport elevation while the flight is within a descent area,
regardless of landing direction.
Descent areas are established for all straight-in instrument approach procedures at an airport and may be
established for runways not served by an instrument
approach procedure to accommodate visual and contact
approaches. More than one runway (descent area) may
be used simultaneously for arriving high performance
airplanes if there is an operational advantage for the pilot
or ATC, provided that the descent area serves the runway of intended landing.
CONTROLLED FLIGHT INTO TERRAIN
Inappropriate descent planning and execution during
arrivals has been a contributing factor to many fatal aircraft accidents. Since the beginning of commercial jet
operations, more than 9,000 people have died worldwide
because of controlled flight into terrain (CFIT). CFIT is
described as an event in which a normally functioning
aircraft is inadvertently flown into the ground, water, or
an obstacle. Of all CFIT accidents, 7.2 percent occurred
during the descent phase of flight.
The basic causes of CFIT accidents involve poor flight
crew situational awareness. One definition of situational
awareness is an accurate perception by pilots of the factors and conditions currently affecting the safe operation
of the aircraft and the crew. The causes of CFIT are the
flight crews’ lack of vertical position awareness or their
lack of horizontal position awareness in relation to the
ground, water, or an obstacle. More than two-thirds of
all CFIT accidents are the result of an altitude error or
lack of vertical situational awareness. CFIT accidents
most often occur during reduced visibility associated
with instrument meteorological conditions (IMC), darkness, or a combination of both.
The inability of controllers and pilots to properly communicate has been a factor in many CFIT accidents.
Heavy workloads can lead to hurried communication
and the use of abbreviated or non-standard phraseology.
The importance of good communication during the
arrival phase of flight was made evident in a report by an
air traffic controller and the flight crew of an MD-80.
The controller reported that he was scanning his
radarscope for traffic and noticed that the MD-80 was
descending through 6,400 feet. He immediately
instructed a climb to at least 6,500 feet. The pilot
responded that he had been cleared to 5,000 feet and
then climbed to… The pilot reported that he had “heard”
a clearance to 5,000 feet and read back 5,000 feet to the
controller and received no correction from the controller.
After almost simultaneous ground proximity warning
system (GPWS) and controller warnings, the pilot
climbed and avoided the terrain. The recording of the
radio transmissions confirmed that the airplane was
cleared to 7,000 feet and the pilot mistakenly read back
5,000 feet then attempted to descend to 5,000 feet. The
pilot stated in the report: “I don’t know how much clearance from the mountains we had, but it certainly makes
clear the importance of good communications between
the controller and pilot.”
ATC is not always responsible for safe terrain clearance for the aircraft under its jurisdiction. Many times
ATC will issue en route clearances for pilots to proceed off airway direct to a point. Pilots who accept this
45°
22 NM Radius
45°
5000 Feet
Above Airport
Elevation
Base Line
5 NM 5 NM
5000 Feet
Above Airport
Elevation
5000 Feet
Above Airport
Elevation
Figure 4-11. Typical Descent Area for Straight-In Approach.
type of clearance also are accepting responsibility for
maintaining safe terrain clearance. Know the height of
　
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本文鏈接地址：Instrument Procedures Handbook (IPH)儀表程序手冊上(95)