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has been specifically assigned by ATC. Standard
Instrument Departures are air traffic control (ATC)
procedures printed for pilot/controller use in graphic
form to provide obstruction clearance and a transition
from the terminal area to the appropriate en route
structure. SIDs are primarily designed for system
enhancement and to reduce pilot/controller workload.
ATC clearance must be received prior to flying
a SID. All DPs provide the pilot with a way to depart
the airport and transition to the en route structure
safely. Pilots operating under 14 CFR Part 91 are
strongly encouraged to file and fly a DP at night,
during marginal Visual Meteorological Conditions
(VMC) and Instrument Meteorological Conditions
(IMC), when one is available. The following
paragraphs will provide an overview of the DP
program, why DPs are developed, what criteria are
used, where to find them, how they are to be flown,
and finally pilot and ATC responsibilities.
a. Why are DPs necessary? The primary reason is
to provide obstacle clearance protection information
to pilots. A secondary reason, at busier airports, is to
increase efficiency and reduce communications and
departure delays through the use of SIDs. When an
instrument approach is initially developed for an
airport, the need for DPs is assessed. The procedure
designer conducts an obstacle analysis to support
departure operations. If an aircraft may turn in any
direction from a runway, and remain clear of
obstacles, that runway passes what is called a diverse
departure assessment and no ODP will be published.
A SID may be published if needed for air traffic
control purposes. However, if an obstacle penetrates
what is called the 40:1 obstacle identification surface,
then the procedure designer chooses whether to:
1. Establish a steeper than normal climb
gradient; or
2. Establish a steeper than normal climb
gradient with an alternative that increases takeoff
minima to allow the pilot to visually remain clear of
the obstacle(s); or
3. Design and publish a specific departure route;
or
4. A combination or all of the above.
b. What criteria is used to provide obstruction
clearance during departure?
1. Unless specified otherwise, required obstacle
clearance for all departures, including diverse, is
based on the pilot crossing the departure end of the
runway at least 35 feet above the departure end of
runway elevation, climbing to 400 feet above the
departure end of runway elevation before making the
initial turn, and maintaining a minimum climb
gradient of 200 feet per nautical mile (FPNM), unless
required to level off by a crossing restriction, until the
minimum IFR altitude. A greater climb gradient may
be specified in the DP to clear obstacles or to achieve
an ATC crossing restriction. If an initial turn higher
than 400 feet above the departure end of runway
elevation is specified in the DP, the turn should be
commenced at the higher altitude. If a turn is
specified at a fix, the turn must be made at that fix.
Fixes may have minimum and/or maximum crossing
altitudes that must be adhered to prior to passing the
fix. In rare instances, obstacles that exist on the
extended runway centerline may make an “early
turn” more desirable than proceeding straight ahead.
In these cases, the published departure instructions
will include the language “turn left(right) as soon as
practicable.” These departures will also include a
ceiling and visibility minimum of at least 300 and 1.
Pilots encountering one of these DPs should preplan
the climb out to gain altitude and begin the turn as
quickly as possible within the bounds of safe
operating practices and operating limitations. This
type of departure procedure is being phased out.
2/17/05 AIM
Departure Procedures 5−2−5
NOTE−
“Practical” or “feasible” may exist in some existing
departure text instead of “practicable.”
2. The 40:1 obstacle identification surface
begins at the departure end of the runway and slopes
upward at 152 FPNM until reaching the minimum
IFR altitude or entering the en route structure.
3. Climb gradients greater than 200 FPNM are
specified when required for obstacle clearance and/or
ATC required crossing restrictions.
EXAMPLE−
“Cross ALPHA intersection at or below 4000; maintain
6000.” The pilot climbs at least 200 FPNM to 6000. If 4000
is reached before ALPHA, the pilot levels off at 4000 until
passing ALPHA; then immediately resumes at least
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AIM航空信息手册2004上(170)
