OVERSPEED PREVENTIONThe flight crew should apply the OVERSPEED PREVENTION procedure if the aircraft encounters significant speed variations close to VMO/MMO during the flight.
In this case, the flight crew should keep the Autopilot (AP) and the Autothrust (A/THR) engaged. The use of AP and A/THR enables the aircraft to remain on the intended flight path while thrust reduces to idle (if necessary).
The flight crew should decrease the speed target in order to increase the margin to VMO/MMO (at high altitudes the flight crew should not reduce the speed below green dot speed). After selection of the lower speed target, the flight crew should monitor the speed trend arrow on the Primary Flight Display (PFD). If the aircraft continues to accelerate, and if the speed trend arrow approaches or exceeds VMO/MMO, the flight crew should use the appropriate position of the speed brakes, depending on the rate of acceleration. The length of the speed trend is a good indication of the rate of acceleration.
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[TD="class: note_label"]Note:[/TD]
[TD="class: note_text"]The use of speed brakes is an efficient way to decelerate that is certified for the entire flight envelope. However, the use of speed brakes increases VLS and reduces the buffet margin at high altitudes. The use of speed brakes results in pitch up for which the AP and the normal law compensate.[/TD]
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For descents in descent (DES) and managed speed modes, the flight crew should enter descent wind data that is as accurate as possible in the Flight Management and Guidance System (FMGS). The FMGS then computes an optimized vertical profile that offers a better capability to remain in the speed target range.
OVERSPEED RECOVERY
The OVERSPEED warning is triggered when the speed exceeds VMO +4 kt/MMO +M 0.006, and lasts until the speed is below VMO/MMO. In this case, the flight crew must apply the OVERSPEED RECOVERY procedure.
The flight crew should keep the AP engaged in order to minimize the vertical load factors. In order to minimize overspeed, the flight crew should extend the speed brakes to the most appropriate lever position, depending on the overspeed situation. In addition, the flight crew should keep the A/THRengaged and should check that the thrust reduces to idle.
Disconnection of the A/THR has the same effect on the overspeed recovery than the set of the manual thrust on idle. Both techniques result in the same engine response in terms of thrust reduction.
In the case of severe overspeed, the AP automatically disengages and then the High Speed Protection activates (except when in direct law). As a result, the aircraft encounters an automatic pitch up. Refer to FCOM/DSC-27-20-10-20 Protections - High Speed Protection.
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[TD="class: note_label"]Note:[/TD]
[TD="class: note_text"]The AP does not automatically disengage as soon as the speed reaches the green bars (that represent the threshold when the High SpeedProtection activates) on the PFD. The AP disengagement depends on the speed variations and the High Speed Protection logic.[/TD]
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The High Speed Protection is designed to request the appropriate demand of vertical load factor. Therefore, the flight crew should smoothly adjust the pitch attitude to avoid excessive load factors.
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[TD="class: note_label"]Note:[/TD]
[TD="class: note_text"]The flight crew must disregard the Flight Director (FD) orders while the high speed protection is active. The FD orders do not take into account the High Speed Protection.[/TD]
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The flight crew should keep the speed brakes because the use of the speed brakes is compatible with the HighSpeedProtection.
