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What is the necessity of Obstacle Departure Procedure(ODP)?

Standard Instrument Departure(SID) is enough, isn't it?

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  • $\begingroup$ This question is closely related, but it doesn't address the difference between an ODP and a SID so I don't think it's an exact dupe $\endgroup$ – Pondlife Jun 7 '17 at 14:21
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Departure procedures are way to get IFR traffic from the airport to the en route system. There are four different procedures.

If an aircraft may turn in any direction from a runway within the limits of the assessment area and remain clear of obstacles that runway passes what is called a diverse departure assessment and no ODP is published. There are a few in Kansas and Nebraska but Florida, which is also pretty flat, only has a couple at military bases.

Obstacle Departure Procedures (ODP) are only used for obstruction clearance and do not include ATC related climb requirements. They often have higher visibility minimums and climb rates greater than 200 fpnm. Most are given as text, though occasionally there are graphical representations of them. They frequently have other restrictions, e.g. the tower must be open and monitoring a VOR, not available if local altimeter setting is not available. All but a few airports have an obstacle departure procedure.

A Standard Instrument Departure (SID) is an ATC-requested and developed departure route. Pilots must have at least the textual description of the procedure. SIDs always have a graphical depiction. Unlike Obstacle Departure Procedures, SIDs usually have portions where the altitude is restricted—either minimum or maximum. Most SIDs have multiple transitions to get you into the en route system. Small airports generally do not have SIDs and most airports that have scheduled air carrier service have at least one SID. While the primary purpose of a SID is to ease pilot and controller workload while getting the aircraft into the system, they also provide obstacle clearance.

A visual climb over airport (VCOA) is a departure option for an IFR aircraft, operating in VMC equal to or greater than the specified visibility and ceiling.

A radar departure is another option. They are established when ATC has a need to vector aircraft on departure to a particular ATS Route, NAVAID, or fix.

All departures (except VCOA) assume that the aircraft will cross the departure end of the runway at 35' or more, continue on the runway heading until reaching 400', and climb at a rate of 200 feet per nautical mile. Standard minimum visibility applies, 1 mile for 1 and 2 engines and ½ mile for 3+ engines.

You can read more about departure procedures in FAA-H-8083-16 Instrument Procedures Handbook, Chapter 1 Departures

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Edited because I'm a moron and missed the intent of his question...

This gets deep into the weeds of Pt. 25 vs. Pt. 91 vs. Pt. 135/121.

First off, SIDs are intended for normal all-engine climb to transition from the terminal area into enroute airspace. They aren't specifically designed for obstacle avoidance though it is an important consideration. They don't account for obstacles within the first mile of the runway end, so just relying on SID gradient doesn't protect you against close-in obstacles.

I cribbed this from the FAA Instrument Flying Handbook regarding ODPs:

If an aircraft may turn in any direction from a runway within the limits of the assessment area and remain clear of obstacles that runway passes what is called a diverse departure assessment, and no ODP is published.

So ODPs can be created in conjunction with a SID if obstacles are a problem. "DUH" on my part...

Engine-out ODPs are created by individual operators (airlines etc) and intended only for use in an emergency: engine failure post-V1. It's easier if the engine-out path mirrors a SID, but it doesn't have to. Vertical obstacle clearance is less stringent than SID, but the 0.8% gross vs. net margin (assuming we're talking twin engine) provides a steadily increasing pad over distance.

SIDs/ODPs vs. engine-out ODPs is probably one of the most misunderstood subjects I've encountered in this business. The other is conflating "Climb" with "Obstacle Clearance" to mean the same thing, but there are subtle differences. I suspect both arise from instruction methods and rules of thumb that have evolved and been passed along over the years - if you're Joe Pilot with no access to an obstacle database, about the only recourse you have is to use the SID and hope there's nothing inside that first mile that you might hit (-ahem- MDW and TEB).

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    $\begingroup$ Why do you say that ODPs are "only for use in an emergency"? I'm fairly sure they aren't, and ATC can even assign them to you. $\endgroup$ – Pondlife Jun 7 '17 at 17:04
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    $\begingroup$ You may want to structure your post in paragraphs with blank lines. $\endgroup$ – mins Jun 7 '17 at 18:31
  • $\begingroup$ Ah...I got you. I thought you meant engine-out ODPs. $\endgroup$ – PHChilly Jun 7 '17 at 19:05

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