On 21 March 2001 an Airbus A320-200, operated by Lufthansa, experienced a flight controls malfunctions shortly after take-off which resulted in loss of control and subsequent near terrain impact. The uncontrolled roll, due to the malfunction of the pilot flying's sidestick, was recovered by the other pilot and the aircraft safely returned to land in Frankfurt without further incident.
The following is an extract from the official Report 5X004-0/01 on the serious incident by Bundesstelle für Flugunfalluntersuchung - BFU (Federal Bureau of Aircraft Accidents Investigation, Germany):
[…] "Immediately following the lift-off the aeroplane assumed a slight bank angle to the left. The commander, who was the pilot flying, tried to correct the attitude by a slight input on the left sidestick. However, the bank angle increased continuously up to approx. 22°. With the commander’s call out :“I can’t do anything more“ the first officer took over the controls with the words “I have control“ and pressed the TAKE OVER PUSH BUTTON. The First Officer had already beforehand instinctively tried to counteract the rolling movement with his sidestick.
Controlled by the second autopilot the aeroplane climbed to flight level FL 120 where the crew cautiously analysed the control system. With an input on the left sidestick the aeroplane - after a short shaking and a brief bank angle corresponding to the input - suddenly reacted contrary. The right-hand sidestick functioned normally.
The crew decided to not continue the flight but to return to Frankfurt. The First Officer took over the controls and safely landed the aeroplane in Frankfurt. […]
Prior to this flight, the aeroplane had already been at the maintenance organisation for two days for repair purposes. On several previously conducted flights had problems occurred on one of the two elevator aileron computers (ELAC), which control, among other things, the bank angle. When the computer was replaced, a bent pin, which could not be repaired, was found on the plug of the ELAC no. 1. Therefore the whole plug of the ELAC no. 1 was replaced and rewired. Two pairs of wires were connected inverted, the Command Channel and the Monitor Channel."
After thorough investigation, the Report reveals that numerous factors have contributed to this occurrence. The causal chain was never interrupted before the incident. Section 3.2 titled “Causes” describes the set of causes that led to the event:
The BFU has come to the conclusion that the serious incident is due to the fact that:
- during repair work on the plug of the Elevator Aileron Computer (ELAC) no. 1 two pairs of wires had been connected inverted
- the error remained undetected
- the error was not recognized by the flight crew during the “FLIGHT CONTROL CHECK“.
Contributing factors were:
- an unclear and difficult to handle documentation so that a wrong wiring diagram was used
- diversion from the manufacturer’s data by the Maintenance Support
- manufacturer’s instructions which are not formulated unambiguously
- functional check by the cross checking staff member was carried out incorrectly
- insufficient functioning of the quality assurance
- the lack of supervision of the maintenance organisation by the operator
- a quantitatively and qualitatively insufficient supervision of the maintenance organisation and the operator by the supervising authority
- deficiencies in the “AFTER START CHECKLIST“ for the conduct of the “FLIGHT CONTROL CHECK“.
The Report produces the following recommendation for immediate action addressed to LBA (Luftfahrt-Bundesamt - the Federal Office of Civil Aeronautics) and to the aircraft operator concerned:
The procedures and checklists for all fly by wire aeroplanes should be amended in such a way that during the flight control check attention is paid to the correct direction of movement of the ailerons and roll spoilers as recommended also by the manufacturer.
The BFU Report further provides a number of recommendations about the serious incident. The key recommendations are addressing manufacturer documentation issues, the internal quality assurance process of the operator’s maintenance and toward the need for more strict supervision from LBA.