Jetstream 4100, G-MAJD, 29 March 2000

Jetstream 4100, G-MAJD AAIB Bulletin No: 12/2000 Ref: EW/C2000/03/08 Category: 1.1 Aircraft Type and Registration: Jetstream 4100, G-MAJD No & Type of Engines: 2 Garrett Airesearch TPE 331-14GR/HR-807H turboprop engines Year of Manufacture: 1992 Date & Time (UTC): 29 March 2000 at 1400 hrs Location: Manchester Aerodrome (Woodford) Type of Flight: Post maintenance test flight Persons on Board: Crew - 3 - Passengers - None Injuries: Crew - None - Passengers - N/A Nature of Damage: None Commander's Licence: Airline Transport Pilot's Licence Commander's Age: 55 years Commander's Flying Experience: 4,700 hours (of which 325 were on type) Last 90 days - 16 hours Last 28 days - 7 hours Information Source: AAIB Field Investigation History of the flight The aircraft was one of a group scheduled for a wing splice replacement, in accordance with Service Bulletin J41-57-021, which involved the removal of the wing. It was the second aircraft to undergo the Service Bulletin and the work was carried out by a subsidiary of the aircraft manufacturer. The pre-take-off checks for the test flight under 'A' conditions included a "full and free" check of the aileron trim. Soon after take off the pilot attempted to trim out a roll bias but it appeared that the initial application of trim made the situation worse. Further roll trim application aggravated the situation and the pilot then realised that the roll trim was operating in the wrong sense. He reversed the trim input, achieving balanced flight and then returned to the airfield for an uneventful landing. Inspection showed that the aileron trim cables had been wrongly routed around a pair of co-axial pulleys at the wing root and that their connections to the chain, which operates the trim screw jack at the aileron, had been reversed. Aileron trim system On the Jetstream 41, roll trim is achieved through a tab on the left aileron. It is a cable operated manual system. The cables exit the pressure hull at station 360.50, abeam the trailing edge of the wing and descend to a pair of co-axial pulleys at the wing root. These pulleys effect a change of direction in the cable run to take them, without further support, along the aft face of the rear wing spar. The cables emerge from the pressure hull one above the other but route under the twin pulleys so that they exit one behind the other. Within the wing the cables route through common, rather than individual, large aperture fairleads. In their passage outboard along the wing they diverge slightly to attach to the upper and lower end fittings of the trim screwjack chain. The cables terminate in nipples, which have different shank lengths and the chain end blocks are sized so that the longer shanked nipple should not be able to be inserted into the shorter of the two blocks. Pre-flight engineering work The work was managed by a project leader; a CAA licensed aircraft engineer qualified under his delegated company approval to sign for the work carried out. The project leader controlled a team divided into three groups. Two of the groups worked three consecutive 13 1 /2 hour day shifts (including Sunday working) and the third group worked on permanent night shift. The groups maintained a hand-over log. The project leader was present for most of the daytime shift working (2 shifts) and was available at any time on a mobile telephone. In addition to managing the project and manpower allocation within the project, the Project Leader undertook some of the tasks himself, inspected and signed for much of the work. He also had responsibility for signing the Certificate of Release to Service for the aircraft. A second licensed engineer with delegated company approval, working on contract to the company, was also available. The project leader had requested his assistance full time on G-MAJD but, given the workload assessed for the task, it was deemed that it had been adequately resourced. Consequently, the contact engineer was occupied predominantly with work on an ATP aircraft on which he had responsibility for signing the aircraft's Certificate of Release to Service. He worked on a 40 hour, five day a week schedule with overtime as required on week days and Saturdays. His weekly working hours had totalled about 60 for each of the previous two weeks. He had been periodically called upon to work on G-MAJD and, after the major re-assembly of G-MAJD had taken place, he worked more permanently, but not exclusively, on that aircraft. As part of the work to allow the wing to be removed from the fuselage the aileron trim cables had been removed from the trim actuator chain, withdrawn around the wing root pulleys, coiled up and tied at their exit from the pressure hull. This work was performed by an experienced aircraft fitter working with the maintenance company under sub-contract. When the wing flying control cables had been de-tensioned, the fitter had blocked them at places within the fuselage to prevent them becoming dislocated, had colour coded them and had labelled their coiled ends. After the re- attachment of the wing, when he returned to re-install the trim cables, probably on 23 March, he did not find the labels. He then installed the cables in what he thought was their "natural" routing from their exit from the pressure hull downwards to the pulleys at the wing root and then outboard along the wing's rear spar to the chain at the trim screwjack. The trim cables emerge from the side of the fuselage one above the other and engage the co-axial pulleys one behind the other. He made the wrong selection in routing the cables around the pulleys. (He routed the upper cable around the forward pulley and vice versa.) He then routed the cables to the chain attachments so that they did not appear to cross in their passage along the wing rear spar. (Lower cable off the pulley to lower chain fitting; as the pulleys were angled to keep the cable entry and exit in plane, the forward pulley appeared to be lower than the aft.) He was unaware that the cable nipples and chain end fittings were sized to prevent mis-assembly and recalled having no difficulty in connecting the cables to the incorrect chain ends. He tensioned the system, let it settle for 24 hours then re-checked the tension and fitted the security devices. The chain end blocks are sized so that the longer cable end nipple should not fit into the shorter block. The chain end blocks were found to conform to the manufacturing drawings. The drawing of the larger nipple showed it in the pre-swaged condition and so it was not possible to determine whether there had been any non-conformity in the original dimensions of the longer nipple, the swaging process or the design tolerances. The aircraft manufacturer undertook a review of the design and manufacturing of this component which resulted in Service Bulletin J41-27-060. The initial and duplicate inspections (Item 3, see below) were carried out when both approved engineers were present on Friday 24 March. On that day the contract licensed engineer was also occupied with the release to service of the ATP, for which the operator's aircrew had arrived and were waiting. The checks comprised a visual examination of the system's general condition, correct assembly, security and locking plus a re-check of cable tension. Neither of the engineers saw anything anomalous in the trim cable routing and it did not occur to the project leader that the trim cables could be incorrectly connected. In examining the cable nipple engagement in the chain fittings he merely checked that the roll pins, which lock the nipples in place, were installed. On completion of these checks it was not possible to carry out the functional checks (Item 4) because of other demands on G-MAJD and the other aircraft. On Monday 27 March, the contract engineer functionally tested and adjusted the engine controls and this occupied him for most of the mo

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Jetstream 4100, G-MAJD, 29 March 2000

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