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Reducing airspeed during curved departure with engine failure

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Reducing airspeed during curved departure with engine failure

Old 8th Jul 2018, 13:50
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Reducing airspeed during curved departure with engine failure

The following paragraph in an airline B737NG Operations Manual has me wondering. It refers to an engine failure requiring a curved departure.

"The radius of turn will be based on TAS (IAS V2, corrected for an airport reference temperature and airport elevation +500 ft). In some cases, different temperature and speed may be considered. The flight director pitch bar will command V2 to V2+20 knots depending on what speed the engine failure occurred at. Consequently it may be necessary to look ‘through’ the Flight Director pitch bar to ensure V2 is flown during the turn."

My understanding is that the FD pitch bar commands the speed at which the engine failure occurred; not exceeding V2 plus 20 knots and that you do not deliberately pull the nose up or reduce power in order to reduce the speed back to V2 during the turn - or at any other time with engine failure on take off. You should not have to "look through" a FD since Boeing state if the FD is not giving you the information you want, you should switch it off.
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Old 8th Jul 2018, 14:59
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Fly the FD pitch for speed, never reduce pwr until emergency turn finished.
If you are at V2 +20 you are fine as the failure happened after V1 and V2 and you had two engines until then and are above the N-1 profile.
Dont get fancy!
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Old 8th Jul 2018, 16:36
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Why do you need a flight director ?
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Old 9th Jul 2018, 00:31
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If you are at V2 +20 you are fine as the failure happened after V1 and V2 and you had two engines until then and are above the N-1 profile

A bit of caution needed. First, in a turn, the concern usually is obstacles to the side .. not below the aircraft. A concern with the turn is turn radius and how this fits in among the rocky bits. Too slow and you might hit an inside obstacle .. too fast, an outside one. Your escape procedure should talk about what speeds to fly ... you should fly speed in accordance with the procedure. It follows that the procedure designer should have made sure that the procedure technique is compatible with AFM requirements.
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Old 9th Jul 2018, 02:25
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The procedure designer should also consider the procedure is within the capability of an average crew who are having a bad night! Not always the case!
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Old 9th Jul 2018, 05:48
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CASA caused this drama regarding looking through the FD and reducing speed, with respect to instrument rating checks and the requirement to fly V2 - V2+5. It is rubbish and not relevant to the aircraft operation.

The Boeing manual clearly states how the FD commands pitch for speed depending on the time of the failure. The commands result in a profile that meets take off performance.

Special procedures may be designed around separate criteria, but they will be listed if flying the normal profile does not meet the criteria.
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Old 9th Jul 2018, 09:32
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Special procedures may be designed around separate criteria ...

The straight ahead takeoff normally is fine for following the FD guidance (if one really must do that ...).

However, while the escape procedure should endeavour to cater for a reasonably normal speed variation, sometimes that just isn't feasible and the nominated procedure speed (or speed range) needs to be flown to keep the splays where they need to be ...
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Old 9th Jul 2018, 11:54
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J_T

Here in the US the obstacle clearance is only 200' horizontally within the airport boundaries and only 300' horizontally after passing the boundaries
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Old 10th Jul 2018, 04:44
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Makes no difference to the practice, though. If the splay is put between rocky bits, the radius of turn is linked to speed. Mind you, 300 ft, to me, is not much to play with ...
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