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Engine Out Procedure with IAS restriction in the 3rd Segment

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Engine Out Procedure with IAS restriction in the 3rd Segment

Old 17th Feb 2020, 01:19
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VC9
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Engine Out Procedure with IAS restriction in the 3rd Segment

The company that I work for has a number of engine out procedures that require that have airspeed restrictions during clean up in the 3rd segment. To do this the flight mode has to change from take-off to speed select and level change resulting in the aircraft climbing above the engine out acceleration altitude until the point where the speed restriction no longer applies and then accelerating again to finish the clean up.
I believe that this procedure is unacceptable and have expressed my concern but no action is being taken.
From my experience in this area I maintain that the design of an engine out procedure must ensure that the 3rd segment can be flown as a level segment with no interruption to the level acceleration until the aircraft is clean.
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Old 17th Feb 2020, 01:53
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Couldn't you make the turn at V2 and start acceleration once the turn with the speed restriction has been completed?
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Old 17th Feb 2020, 02:03
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VC9
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Originally Posted by FlyingStone View Post
Couldn't you make the turn at V2 and start acceleration once the turn with the speed restriction has been completed?
I’ve tried to tell them that the engine out acceleration altitude needs to be raised to ensure that V2 is maintained until the speed restriction no longer applies.

Last edited by VC9; 17th Feb 2020 at 02:13.
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Old 17th Feb 2020, 02:32
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In view of vague information it can only be said that every takeoff gives a maximum OEI acceleration altitudes which is defined by the ten minutes of takeoff thrust. In that case it cannot be raised.
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Old 17th Feb 2020, 03:02
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Are they RNP AR engine out sids?
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Old 17th Feb 2020, 03:12
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VC9
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The aircraft is not RNP AR approved.
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Old 17th Feb 2020, 06:16
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The company that I work for has a number of engine out procedures that require that have airspeed restrictions during clean up in the 3rd segment. To do this the flight mode has to change from take-off to speed select and level change resulting in the aircraft climbing above the engine out acceleration altitude until the point where the speed restriction no longer applies and then accelerating again to finish the clean up.
This is very vague. It will be clear if you give an actual example. What is the speed restriction F, S or GD? and which aircraft is this?

Last edited by vilas; 17th Feb 2020 at 06:39.
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Old 17th Feb 2020, 08:28
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VC9 - Not sure which aircraft your flying, but (depending upon the engaged ADFS modes) taking the aircraft out of TOGA mode typically involves a thrust reduction and also a change in system logic which, in a engine out case might not be prudent given that segment 1,2,3 are assumed to be flown using TOGA mode & thrust throughout. Further more, if a particular speed is required, it should never be less than your V2.

Regarding acceleration during the 3rd segment, there's actually no requirement to fly level; the only requirement is that you do not descend (i.e that you do not trade height for speed) and accordingly your worst case RoC during the 3rd segment is zero (i.e. level).
It should perhaps be remembered that, in case of an engine failure at takeoff, use of Takeoff Thrust (TOGA) is typically certified for a maximum of 10 minutes, i.e. the emergency case (and for a maximum of 5 minutes with all engines operating, i.e. the normal case).
It should also be remembered that Maximum Continuous Thrust (MCT), which is not time-limited, can only be selected once the en-route configuration is achieved (i.e. segments 1,2,3 have been completed).
It is this 10 minute TOGA thrust limit that determines the maximum acceleration height (with the minimum height for acceleration set, as per regulation, at 400 ft AGL).
Finally of course, the takeoff phase (i.e. the four defined segments) is considered as complete once the aircraft is above 1,500 ft AGL, regardless of what configuration the aircraft is in when it climbs above 1,500 ft AGL and, once above which, you no longer need the use of TOGA thrust.

Putting all that another way, let's say that from the start of the take-off run (during which you suffer an engine failure after V1) it takes you 2 minutes to climb to a height 400 ft AGL (i.e. the end of segments 1 & 2 and the start of segment 3). According to the rules, you've now got 8 minutes remaining during which to either get cleaned up (complete the third segment), or else climb (with TOGA and at V2 to V2+20) to 1,500 ft AGL (or higher) and then clean up.
So, having suffered and an engine failure during takeoff, with one very powerful engine still running at TOGA (and maybe also a relatively light aircraft), it's entirely possible that one could climb to above 1,500 ft AGL in a period of 10 minutes from commencement of the takeoff roll. Then, once above 1,500 ft AGL, one can come out of TOGA (remembering the 10' TOGA limit) and accelerate at ones leisure.
The aim of the game is to get safely away from the ground as soon as possible and also get ones remaining engine out of the TOGA thrust mode as soon as possible (i.e. you want to baby that remaining engine).

Regarding this notion of maintaining level flight during the 3rd segment, the acceleration profiles utilised by most AFDS modes such as VNAV and FLCH do not necessarily command the aircraft to fly level at the Acceleration Altitude as it accelerates. E.g. the AFDS in the Boeing B737 commands the Flight Director to give a very slight climb during acceleration. And, somewhat similarly, in the Boeing B757/B767 we usually set V/S +200 fpm during the acceleration phase, i.e. to provide the required acceleration coupled with a gentle rate of climb (mostly to ensure that we do not descend).
Part of this misunderstanding of the requirements probably stems from how the four takeoff segments are usually drawn on paper, plus that the rules were derived & described from aeroplanes that (back in the day) were substantially performance limited when on one engine, in a way that more modern twin jets are not or are less so, and therein they were more likely to bump up against the 10 minute TOGA thrust rule than be able to achieve a height > 1,500 ft AGL (after which point the prescribed takeoff segments become academic) and thus the tendency has always been to fly all four segments as defined, i.e. planning for the worst case performance scenario.

Last edited by Old King Coal; 17th Feb 2020 at 09:38.
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Old 17th Feb 2020, 11:39
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Originally Posted by VC9 View Post
The company that I work for has a number of engine out procedures that require that have airspeed restrictions during clean up in the 3rd segment. To do this the flight mode has to change from take-off to speed select and level change resulting in the aircraft climbing above the engine out acceleration altitude until the point where the speed restriction no longer applies and then accelerating again to finish the clean up.
I believe that this procedure is unacceptable and have expressed my concern but no action is being taken.
From my experience in this area I maintain that the design of an engine out procedure must ensure that the 3rd segment can be flown as a level segment with no interruption to the level acceleration until the aircraft is clean.
While it is not a routine profile, it does occur on occasion. The reason for the speed restriction should be for terrain, it should not be for airspace/ATC/noise etc. If you get part way through flap retraction and get to a limit speed that has to be maintained, and you convert from a level acceleration to a climb at a constant speed, you are still compliant with the rules. At the end of the TO thrust limit time, say 5 minutes or 10 minutes dependent on type and AFM limitation, you are ..."obligated"... to set MCT. At that point if you are still speed limited, then you are required to have the OEI gradient in that condition to maintain level flight and accelerate in due course to clean configuration to conclude the 3rd segment. As the follow on segment has a minimum climb gradient in the clean config, while it will usually not be limiting, you may be performance limited if your circumstances ended up in a high drag config and back at MCT. You can probably assess the extent of a problem by comparing various WAT conditions that would approximate MCT for your blender vs TO thrust.

In the real world, the toss up between complying with a wall clock limit vs avoiding terrain should be fairly simple to prioritise.
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