Synopsis

On 5 November 1997, an Airbus A340-300 operated by Virgin Atlantic airlines experienced a landing gear malfunction. The crew executed a successful partial gear up landing at London Heathrow.

Description

The following extract is from the official UK AAIB Report on the Accident:

The accident occurred when the aircraft, which had a landing gear problem on its final approach to Heathrow Airport, carried out an emergency landing on Runway 27L with the left main landing gear only partially extended, with the Airport Emergency Services in full and effective attendance. The evacuation was completed with minor injuries to 5 passengers and 2 crew members.

Examination of the left main landing gear found that the gear had been jammed by the No 6 wheel brake torque which had disconnected from its brake pack assembly and had become trapped in keel beam structure. The associated torque rod pin was subsequently found beyond the end of Runway 24L at Los Angeles International Airport […]

Cause

The investigation identified the following causal factors:

• Full deployment of the left main gear was prevented by the unrestrained end of the No 6 brake torque rod having become trapped in the keel beam structure within the gear bay, jamming the landing gear in a partially deployed position.
• The torque pin which had connected No 6 brake torque rod to that wheel brake assembly had disengaged during landing gear retraction after take off from Los Angeles, allowing the unrestrained rod to pivot freely about the retained end.
• The torque pin and its retaining assembly had been subject to higher axial and torsional loads than predicted during aircraft braking in service. These loads were the result of elastic deformation of the wheel axle, brake and torque rod, and due to assembly without the correct axial clearance as a result of prior undetected displacement of the associated bushes. The precise mode of failure of the retaining assembly bolt, nut and cotter pin could not be ascertained in the absence of these parts.
• This design of wheel brake assembly had satisfactorily passed the related certification wheel brake structural torque test to the requirements of Technical Standard Order (TSO) C26c paragraph 4.2(b). However the latter contained no requirement to use a representative axle or other means to reproduce the axle deflections which occur during aircraft braking in service, and did not require post torque test strip assessment of brake assemblies for resultant evidence of overstressing deformation which did not produce component failure.

Recommendations

The following recommendations were made as a result of the investigation:

• Airbus Industrie should consider providing a revision to the QRH [Quick Reference Handbook] “Landing with abnormal Landing Gear” procedure to include reference to the considerations of crosswind and choice of landing runway.
• The CAA, FAA and JAA should review the requirements for public transport aircraft cabin door simulators used for crew training to require that they accurately simulate any non-linear characteristics of the associated aircraft doors and to require that full instruction is given to cabin crews regarding the door operating characteristics to be expected when operating the doors in an emergency.
• The CAA, FAA and JAA in consultation should amend the aircraft wheel brake certification structural torque test requirements in (TSO) C26c, paragraph 4.2(b), to require the use of representative wheel axles or other means to reproduce the expected axle deflections and associated brake assembly loads arising in service, and a post-certification torque test strip examination of such assemblies to check for yielding deformation to verify loading behaviour.
• The CAA, FAA and the JAA in consultation should amend the requirements for the integration of the Failure Mode Analysis (FMA) of new design wheel brake assemblies by the aircraft manufacturer to make into account the potential secondary effects of torque rod disconnection upon landing gear operation, in order to assess the related risk of gear jamming due to torque rod fouling on adjacent parts. Where a potential for suhtorque rod fouling is identified, appropriate design action should be required to eliminate this possibility so that landing gear operation is protected.
• In order that the maximum air safety benefit may be obtained from Cockpit Voice Recorders (CVRs) during incident and accident situations where associated aircraft electrical power supplies may be prematurely lost, the FAA and the CAA should commission a study to investigate the feasibility of fitting limited duration independent power supplies to solid state CVRs.
• The JAA should extend the existing JAA-Ops 1.700 requirement, for aircraft above 5,700 kg and certificated after April 1998 to have 2 hour duration CVR recording capability, to include a requirement to retrofit the same weight category of aircraft certificated on, or before, April 1998 with similar recording duration CVRs.

The Final Report of the Investigation was published on 29 June 2000.

Related Articles

• Airworthiness
• Brakes
• Gear-Up Landing (OGHFA SE)