Flight control systems

A Cessna T207A aircraft, with seven persons on board, was departing Jabiru for a local scenic flight. The operator reported that the control rod end for the right aileron disconnected and the aileron deflected upwards shortly after the aircraft had rotated for take-off. The take-off was continued as there was insufficient runway remaining to stop the aircraft. A significant amount of left aileron input was then required to counteract the tendency for the aircraft to roll right. The pilot was able to conduct a normal left circuit and landed the aircraft safely at the departure runway. There were no injuries to passengers or crew, and no damage to the aircraft.

The investigation found that the swivel joint for the rod end, which attached to the outboard end of the right aileron control rod, had fractured and separated at the base of the threaded section. The rod-end fitting consisted of a rounded but flat-sided cast-alloy housing with a threaded tail section, which was attached to the interconnecting drive rod from the wing. The housing contained a spherical bearing with a bolt through the centre (at ninety degrees to the threaded tail) which connected the drive rod to the aileron control surface.

Metallurgical examination confirmed that the rod-end bearing had seized in the housing due to surface corrosion on the sliding surfaces. That action had exposed the threaded shank section of the fitting to elevated bending loads, rather than the push-pull loads for which it was designed. Cracking then initiated and propagated, through about 50% of the rod-end cross section, under normal operating conditions over an extended period before finally separating.

Examination of the maintenance documentation for the aircraft showed that the failed rod end was fitted to the aircraft as a new item on 14 Oct 1999. The rod end failed in service on 13 June 2001. At that time, it had completed a total of 754.3 hours time-in-service. The rod ends did not have a time-in-service life and were listed by the manufacturer as an "on condition" item.

The company reported that it had a policy of changing all control rod swivel-end fittings when their aircraft underwent repainting; approximately every 4-5 years. The investigation was unable to determine why the rod end was not changed at the last repaint.

The crew of the Boeing 737 reported that when the speed brake was selected, during descent into Sydney with the autopilot engaged, the aircraft rolled slightly to the right. The autopilot was disengaged, and the speed brake was again selected with the same result. The speed brake was restowed and the flight continued and landed without further incident.

The operator reported that inspection of the aircraft, on 15 February 2001, revealed that the left-wing number three flight spoiler "UP" cable (P/No. WSA2-3) had failed at a pulley in the left wheel well at Wing Buttock Line (WBL) 73.00. The failure was due to corrosion as evidenced by rust deposits at the failure location. During rectification, all other left wing spoiler cables were replaced due to evidence of minor corrosion. Following repair, the aircraft was returned to service.

The operator reported that, after a previous spoiler cable failure in 1997 due to corrosion, an Engineering Release (ER) had been issued to require the inspection of all spoiler cables at the next Phase 20 check and subsequent 2C check with cable replacement at the next 4C check. Replacement at the 4C check terminated the inspection requirements of the ER.

As a result of the cable failure on 15 February 2001, the ER was revised to require inspection of the cables on an ongoing basis with cable replacement at every 4C check interval to preclude recurrence.

Subsequently, on 28 February 2001, the incident aircraft underwent overnight maintenance at Melbourne. During the maintenance inspection, the left-wing spoiler cables, that had previously been changed at Sydney on 15 February 2001, were found to be mis-routed. The operator's investigation revealed that the maintenance engineers involved in the original rectification had travelled from Brisbane to Sydney that day and had worked a period in excess of 24 hours with minimal breaks. Excessive hours worked and fatigue of the maintenance engineers was considered to have contributed to the misrouting of the cables and the failure to detect the misrouting during a duplicate inspection of the spoiler control system.

During climb-out from Darwin, passengers on the British Aerospace Bae146 advised the cabin manager that about 3 metres of cable was trailing from the trailing edge of the right wing. After the first officer had conducted a visual inspection, the crew advised Darwin ATC that they had a problem and required a return for landing. Fuel was burnt off to achieve maximum landing weight. Controllability checks found no handling problems with the aircraft, which was landed safely.

An inspection identified the trailing cable as an aileron trim cable (upper). Failure of the cable had occurred at the outboard pulley located at wing rib 14. The cable was found to have failed as a result of significant corrosion between the pulley bank and the wing rear spar. Corrosion was also present on the failed cable coinciding with the location of the inboard pulley at wing rib 14. No corrosion was found on the left-wing aileron trim cables. Previous inspection of the area was reportedly carried out during a 6C check in May 1999, 3,495 flight hours earlier.

The aileron trim cable material was zinc coated carbon steel (MIL-W-83420, Type 1, Composition A). Stainless steel trim cables were not available from the aircraft manufacturer.

No other reported failures of BAe146 aileron trim cables were found in a search of the Civil Aviation Safety Authority major defect and ATSB incident databases. The operator advised that corroded cables and seized pulleys at that location had been recorded on various BAe146 aircraft since 1992. The aircraft maintenance manual required special attention for corrosion during inspection of cable sections in contact with pulleys.

While taxiing for departure, the crew of the Boeing 747 selected the flaps to the take-off position. As the flaps extended, the left outboard aileron deflected to the full down position. The aircraft returned to the gate for rectification.

Investigation revealed that the left aileron cable (AA-11), which connected the inboard aileron quadrant to the aileron cable drum at wing station (WS) 776.98, had failed immediately outboard of the cable drum. The adjacent cable (AB-13), which connected the outboard aileron quadrant to the aileron control drum, was frayed at a location consistent with having been in contact with the other cable. The aileron cable drum had four grooves to accommodate the four separate aileron cables which ran inboard and outboard from the drum and connected to the inboard and outboard aileron quadrants. Markers were installed at the WS767 and WS780 locations to provide visual guidance for the routing and attachment of the aileron cables to specific grooves on the cable drum.

The aileron control drum forward guide pin was bent and displayed evidence of abrasion from interference by the cables. There was also abrasion to the top two grooves of the cable drum. Further examination revealed that the two aileron cable markers (decals) attached to the aileron drum's inboard and outboard mounting brackets at WS767 and WS780 were installed incorrectly. The marker for WS767 was fitted at WS780 and vice versa.

The aircraft had been manufactured in 1983 and had operated 62,399 hours to the time of the incident. Since 2 June 1997, when both cables were changed due to wear, the aircraft had operated 1,022 hours. The appropriate dual certifications, for the aileron control system, had been carried out at that time.

The investigation determined that another aircraft in the operator's fleet had had the same aileron cables changed, due to fraying and wear, about 12 months prior to the incident. This aircraft was inspected, and it was found that the aileron cable markers at WS767 and WS780 were also transposed.

The investigation also found that eight other aircraft, from various operators, had aileron cable markers incorrectly installed at the WS767 and WS780 locations. However, it was not possible to determine if the markers had been transposed during, or after, aircraft manufacture.