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Old 1st Mar 2020, 08:31
  #6 (permalink)  
sonicbum
 
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Originally Posted by OPEN DES
Hi FD,

Not entirely true. Whilst what you say gives an acceptable result in most cases, it could start a shallow descent too early, primarily if an excessive decel rate is present (hot/high/heavy).
The way the AP/FD manages the pitch change in OP CLB/DES (speed on elevator) is a sacrifice/exchange ratio between kinetic vs potential energy.
From FCTM : At high flight levels, close to the weight limits, the aircraft speed quickly reduces. Thus, the flight
crew should not delay to descent. The crew must not decelerate below green dot.


When ready for descent, the PF:

- Sets the SPEED and pulls
- Sets the engine out recovery altitude and pulls to engage for OPEN DES



Likewise if you pull OP CLB in the EFATO case (third segment), before reaching Green Dot, the a/c will start a shallow climb in the level segment: Accelerating and climbing at the same time in accordance with the ‘energy ratio’.

So: pull ALT when reaching Green Dot, not before.

brgds

s
From FCTM As the speed trend arrow reaches Green Dot speed, pull for OPEN CLIMB, set THR MCT when
the LVR MCT message flashes on the FMA (triggered as the speed index reaches green dot)
and resume climb using MCT. If the thrust lever are already in the FLX/MCT detent, move lever
to CL and then back to MCT.

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