Event Details

Title:Acceleration to speed well above VMO, Airbus A320-232, G-TTOA
Micro summary:This Airbus A320 accelerated to a speed well above Vmo.
Event Time:2004-04-15 at 0750 UTC
File Name:2004-04-15-UK.pdf
Publishing Agency:Aircraft Accident Investigation Board (AAIB)
Publishing Country:United Kingdom
Report number:EW/G2004/04/14
Site of event:Descent
Destination:Malaga Airport, Malaga, Spain
Airplane Type(s):Airbus A320-232
Flight Phase:Descent
Operator(s):GB Airways
Type of flight:Revenue
Serious Injuries:6
Other Injuries:0
Executive Summary:The co-pilot was acting as handling pilot and the aircraft was level at FL310 with the autopilot engaged in selected SPD (speed) control mode. The aircraft had been descended to FL310 unusually early by Madrid ATC and on commencing the approach for Malaga Airport, the co-pilot initiated a descent in the 'managed' lateral and vertical navigation modes. He also changed the speed target from SPD to MACH control mode. He did this because he thought he must have accidentally selected SPD mode with the SPD/MACH changeover button at some earlier time whilst adjusting the selected Mach number target. At the time he thought that automatic changeover from Mach 0.78 to the equivalent CAS speed of 300 kt should not take place until passing through FL285. After levelling at FL250, further descent to FL130 was initiated in the open descent mode.

On passing FL220 the aircraft was descending at 4,800 ft/min and maintaining a speed of between M 0.78 and M 0.79. The CAS had increased to 349 kt and the Mach number was approaching VMO with the speed trend arrow indicating a continued acceleration to a speed well above VMO.

The commander called "speed" to the co-pilot and a lower Mach number, equivalent to 320 kt CAS, was selected on the FCU although the autopilot and autothrottle were kept in the MACH mode. One second later the autopilot was disconnected and a further second later both pilots simultaneously applied aft stick demands of approximately 10 each in an attempt to prevent an overspeed. This resulted in the aircraft experiencing a sudden increase in normal acceleration, peaking at 2g, before returning to about 1g. For a further eight seconds both pilots continued to make inputs on their respective side stick controllers, with neither pilot pressing their sidestick take-over button. The autothrust remained engaged throughout and no speedbrake was used.
Learning Keywords:Systems - Automation Design
Systems - Flight Control System
Systems - INS/FMS/PMCS mis-entry


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