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Interim Recommendation issued to: Boeing

Recommendation details
Output No: IR19970138
Date issued: 16 September 1997
Safety action status: Closed
Background:

SUBJECT: Boeing 747 Aileron Cable Failure


OCCURRENCE SUMMARY

The crew of the B747 reported that, when taxiing for departure, the left outboard aileron deflected to the full down position when the flaps were selected to the take-off setting. The aircraft returned to the gate where investigation revealed that one of the left aileron cables was broken and another was frayed.


ANALYSIS

The Boeing B747 aileron control system comprises a cable loop system located on the wing rear spar (refer figure 1).

In this occurrence involving aircraft Serial Number 23029, the left aileron control cable (AA-11) failed and an adjacent cable (AB-13) was severely worn and frayed (see figure 2). It was apparent that the two control cables were misaligned on the cable drum (Part Number 65B80583-1) located at wing station WS776.98 on the rear spar. The forward cable drum guide pin exhibited signs of wear consistent with being abraded by a control cable. The aircraft had completed 1,022 flight hours since both cables had been replaced on 2 June 1997, approximately 11 weeks prior to the occurrence.

Another of the operator's aircraft, Serial Number 23028, had the AB-13 cable replaced due to excessive wear on 23 July 1996. This cable was frayed down to one remaining strand (see figure 3).

The investigation has revealed that the two aileron control cable decals on the cable drum inboard and outboard mounting brackets at WS767 and WS780 on both aircraft had been incorrectly fitted. The placard for WS767 was fitted at WS780 and vice versa. This transposition results in incorrect cable location information at the cable drum and may lead to incorrect cable positioning during installation (see figures 4 and 5).

The investigation has also revealed that to date, eight aircraft from various operators have had the cable decals incorrectly fitted. Boeing in-service activities Report 92-05, (2 April 1992) details similar cable wear occurrences to three other aircraft, and attributes the cable wear to mis-routing of the cables. No information is given on the aileron control cable decals.

It has not been determined whether the incorrect cable drum decal installation had been carried out during or after aircraft manufacture.

Additionally, Boeing issued Service Letter 747-SL-27-98-A (6 May 1991), which covered incorrect aileron control cable decals at WS1336.971. It is therefore possible that incorrect decals are located throughout the aileron cable control system.


SAFETY DEFICIENCY

The incorrect placement of the B747 aileron control cable location decals on the cable drum located at WS776.98 has the potential to cause misalignment of the aileron control cables during installation, which can lead to a cable failure and a reduction in the effectiveness of the aileron control system.

Output text

The Bureau of Air Safety Investigation recommends that Boeing Commercial Airplane Group issue service information and appropriate corrective action to applicable B747 operators requiring fleet checks for:

(i) correct placement of aileron control cables on the cable drum located at WS776.98; and

(ii) correct installation of aileron cable position decals at WS767 and WS780.

Initial response
Date issued: 14 November 1998
Response from: Boeing Co
Action status: Closed - Accepted
Response text:

The reference cover letter provided a copy of your report of an incident involving a 747-300 airplane, Serial Number 23029. The report indicates that one of the left aileron cables was broken during taxi prior to departure. The report stated that the aileron cable failures may be due to misroutng which may occur as a result of incorrectly installed markers. A check by the Australian Bureau of Air Safety Investigation found eight airplanes with incorrectly installed markers.

Your report recommended that Boeing initiate a fleet check for proper placement of the aileron control cables at Wing Station (WS) 776.98 and correct installation of aileron cable markers at WS 767 and 780.

It has not been determined whether the incorrect marker installations occurred during or after manufacture. As a result of these findings, we plan to issue a service bulletin to 747 operators recommending fleet checks of all 747 airplanes prior to Line Position 1130, except Line Position 1122, for

1, Correct routing of aileron control cables on the aileron cable drum located at wing station 777
2. Correct installation and replacement as required, of aileron cable position markers at wing station 767 and wing station 780

Airplane Line Position 1130 was delivered in September 1997. Airlane Line Position 1122 was checked at Boeing.

A review of the applicable engineering drawings shows that the marker installation and cable installation drawings are correct, and have always been correct. In addition, a check of airplanes in the factory and on the flight line indicates that both the markers and cables are currently being installed per drawing.

If you have any questions, please do not hesitate to contact me at any time.

ATSB response:

ATSB Note: Airworthiness directive 99 - 11- 15 was issued by the FAA which implemented the suggested action.

 
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Last update 01 April 2011