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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 within the limits of the assessment
area (see paragraph 5−2−8b2) 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.
NOTE−
“Practical” or “feasible” may exist in some existing departure
text instead of “practicable.”
2. The 40:1 obstacle identification surface
(OIS) begins at the departure end of runway (DER)
and slopes upward at 152 FPNM until reaching the
minimum IFR altitude or entering the en route structure.
This assessment area is limited to 25 NM from
the airport in nonmountainous areas and 46 NM in
designated mountainous areas. Beyond this distance,
the pilot is responsible for obstacle clearance if not
operating on a published route, if below (having not
reached) the MEA or MOCA of a published route, or
an ATC assigned altitude. See FIG 5−2−1. (Ref 14
CFR 91.177 for further information on en route altitudes.)
NOTE−
ODPs are normally designed to terminate within these distance
limitations, however, some ODPs will contain routes
that may exceed 25/46 NM; these routes will insure
obstacle protection until reaching the end of the ODP.
A71I1M0.65R CHG 2 37//1315//078
2/14/Departure Procedures 5−2−7
FIG 5−2−1
Diverse Departure Obstacle Assessment to 25/46 NM
3. Obstacles that are located within 1 NM of the
DER and penetrate the 40:1 OCS are referred to as
“low, close−in obstacles.” The standard required
obstacle clearance (ROC) of 48 feet per NM to clear
these obstacles would require a climb gradient greater
than 200 feet per NM for a very short distance, only
until the aircraft was 200 feet above the DER. To
eliminate publishing an excessive climb gradient, the
obstacle AGL/MSL height and location relative to the
DER is noted in the “Take−off Minimums and
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