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Hey Leadsled...

Big Picture

Oct 1, 2005
Total Time
A couple of months ago you posted a reply about second segment climbs. In it you gave the following link:

"As for differences between TERPS and Part 25 one engine inoperative performance, I'll direct you to a draft AC. It does a much better job of explaining the differences than I can:



That link is now dead and I wasn't able to find it by searching the FAA web site. Would you happen to still have a link to this document some other way?

Thanks for your help. Searching through your posts on these matters has been invaluable.

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Lead Sled

Sitt'n on the throne...
Apr 1, 2004
Total Time
> enuf
The link is dead. I'll see if I can find it anywhere else. In the mean time, here is the text of the draft AC. I've also included the text of the 1997 American Airlines Flight Operations Bulletin for your reference as well.


Initiated By: AFS-400
AC No: 120-OBS-11

a. Standard Instrument Departures (SIDS) or departure procedures (DPs) based on U.S. Standards for Terminal Instrument Procedures (TERPS) or ICAO Pans-Ops are based on normal (all-engine) operations. Thus, engine-out obstacle clearance requirements and the all-engine TERPS requirements are independent. Engine-out procedures do not need to meet TERPS requirements. Further, compliance with TERPS climb gradient requirements do not necessarily assure that engine-out obstacle clearance requirements are met. Terminal instrument procedures typically use specified all-engine climb gradients to an altitude, rather than certified engine-out airplane performance. Terminal instrument procedures typically assume a climb gradient of 200 feet per nautical mile (nm) unless a greater gradient is specified. For the purposes of analyzing performance on procedures developed under TERPS or Pans-Ops, it is understood that any gradient requirement, specified or unspecified, will be treated as a plane which must not be penetrated from above until reaching the stated height, rather than as a gradient which must be exceeded at all points in the path. Operators must comply with FAR requirements for the development of takeoff performance data and procedures. There are differences between TERPS and engine-out criteria, including the lateral and vertical obstacle clearance requirements. An engine failure during takeoff is a non-normal condition, and therefore, takes precedence over noise abatement, air traffic,
SID's, DPs, and other normal operating considerations.


Flight Operations Technical Informational Bulletin
May 1997 Number 97-03

Obstacle Clearance on SIDs

Distribution List 600 - All Cockpit Crewmembers
This bulletin for information only. Retain or destroy at your option.

Aircraft climb capability on Standard Instrument Departures is more than adequate during normal, all-engine, operations. SIDs are designed so that a climb gradient of no more than 200 feet per nautical mile will provide obstacle clearance, or, if a steeper climb is required, it will be specified on the SID chart. However, if an engine failure occurs while flying the SID two questions arise.

1. Has the flight path specified in the
SID been analyzed for engine-out capability?
2. Have the TPS weight limits been adjusted to account for the terrain or obstructions on the SID if an engine fails?

Obstacle Clearance Criteria

FARs require that operators adjust maximum allowable takeoff weights to ensure obstacle clearance following an engine failure at V1. The aircraft must clear all obstacles (man-made or terrain) in the flight path by horizontal and vertical margins specified in the FARs. The vertical margin is 35 feet at the end of the runway, increasing incrementally with distance from the runway.

The horizontal margin, which accounts for factors such as crosswind and piloting variables, begins with a width of 300 feet on either side of the flight path, increasing to 2000 feet for straight-out flight path, or 3000 feet for turning flight path. If the engine-out runway analysis determines that a limiting obstacle exists in the straight-out path the takeoff weight must be restricted, or a special turning procedure must be provided to avoid the obstacle. This procedure will normally be published on an Ops Advisory page for the airport.

TPS Obstacle Clearance Analysis

The TPS is programmed to adjust runway limited takeoff weights as necessary so that the engine-out performance will meet the obstacle clearance requirement. The flight path for engine failure analysis is assumed to be along the extended runway centerline or the
flight path specified on a special engine failure procedure.

In the event of an engine failure after the completion of the third segment climb (flap / slat retraction), the departure procedure (SID, radar vector, or climb on course) is not analyzed for engine-out obstacle clearance because of the infinite number of variables.

Flying After the Engine Failure

If an engine failure occurs at V1, obstacle clearance has been analyzed for a straight-out path or a special engine-out departure path. If any other flight path is flown prior to the completion of the third segment climb (flap / slat retraction), obstacle avoidance is the responsibility of the flight crew. Furthermore, after the completion of the third segment climb (flap / slat retraction) or the published engine-failure departure procedure, the flight crew becomes responsible for terrain avoidance. It is unlikely, but possible, that rising terrain in the takeoff path could result in an obstacle being below the required margin, but penetrating the GPWS envelope resulting in a "TERRAIN TERRAIN" or "TOOLOW GEAR" warning. Unless visibility is sufficient to assure obstacle clearance, it must be assumed that the GPWS warning
is valid so escape procedures must be accomplished to the extent possible given the configuration and available climb capability.

An engine failure after the airplane is established on a SID may require a climb gradient of 200 feet per mile (or higher if specified by the procedure) to assure obstacle clearance (this is about 800 fpm climb at 240 knots ground speed). At average takeoff weights our airplanes can generally maintain this climb gradient with an engine failure, however at heavy weights, especially with anti-ice on, the climb capability may be as little as 70-90 feet per nautical mile. If the necessary climb gradient cannot be maintained, the flight crew must be aware of obstacles and take whatever emergency action may be necessary to avoid them.


Runway analysis is a tool with inherent limitations. It is intended to ensure engine-out obstacle clearance from lift off through the third segment climb (flap / slat retraction).

After the "top of climb" waypoint, the Mountainous Terrain program will begin to analyze the route of flight and provide driftdown enroute engine-out alternates if the engine-out performance does not permit continuation of flight.

In the event of an engine failure between the completion of third segment climb (flap / slat retraction) and the "top of climb", the flight crew must maintain situational awareness and avoid terrain.

We have asked Jeppesen to provide terrain features on STARs and SIDs especially in areas of high, or rising, terrain. In the meantime, obstacle and terrain information can be found on approach charts, 10-1 area charts and other sources. The Air Traffic Controller, GPWS and Enhanced GPWS may offer additional information and warnings.
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