BFO93IA176

During the night instrument landing system approach, the first officer was unable to keep the airplane aligned with the localizer. The captain took the controls and was forced to utilize full right aileron and full right aileron trim to keep the airplane level. A missed approach was executed and an emergency was declared. The crew performed another approach with 'severe aileron problems' but landed safely. An examination revealed a separated aileron cable. Metallurgical analysis revealed that the cable was severely worn, which caused the separation. The airplane underwent a 'c' check inspection about 2,582 hours prior to the incident. No records were found to indicate the aileron cables were adequately inspected or replaced.

History of flight

On September 15, 1993, about 0108 hours eastern standard time, N870BX, a Douglas DC-8-63, operating as American International Airways Flight 1827, had an aileron flight control malfunction while performing an instrument landing system (ILS) approach into Toledo Express Airport, Toledo, Ohio. The airplane was landed safely and was not damaged. None of the three crewmembers and four non-revenue passengers were injured. Instrument meteorological conditions prevailed and an instrument flight rules flight plan was filed. The flight departed from Atlanta, Georgia, and was conducted under 14 CFR 121.

According to the captain, the first officer was performing the ILS approach to runway 25. The runway was sighted when the airplane was about 500 feet above the ground. The captain stated that the first officer was unable to keep the airplane on the localizer. The captain took the controls and ". . . was forced to put full right aileron and full right aileron trim to hold the aircraft level." A missed approach was initiated and an emergency was declared. The captain returned for another ILS approach to runway 25 while attempting to resolve the aileron problem. The malfunction persisted and an emergency landing was made ". . . with severe aileron problems."

An examination of the airplane revealed a separated aileron bus cable. The cable, aileron power control valve and actuator were replaced and the airplane was test flown by the same crewmembers. During the flight, the aileron system operated normally; however, the captain reported that ". . . the yaw damper caused full deflection of right rudder back and forth." With the yaw damper disengaged, the crew landed the airplane uneventfully.

Aircraft information

A Safety Board maintenance group factual report was prepared and is attached. According to the report, the airplane, a Douglas Aircraft Company (DAC) DC-8-63 was manufactured in 1969. American International Airways became the operator of the airplane on December 6, 1991; it had accumulated 48,193 hours and 23,028 cycles by this date. At the time of the aileron control failure, the airplane had accumulated 51,495.1 hours.

Records provided by the operator indicate the last "C" check (to be performed at intervals not to exceed 3,000 hours) began on N870BX on May 17,1992, and was completed on June 12, 1992, at 48,913 hours total time, and 23,453 total cycles, approximately 2,582 hours prior to the incident.

According to operator records, the aileron cable failed at the left outboard aileron where aileron bus segment "AB-A", part number 3654950-536, routes through the outboard aileron bus crank. The operator was unable to locate any records that would indicate N870BX's aileron cables had been replaced prior to the incident and after acquiring the airplane on December 6, 1991.

According to DAC, the mechanically-linked portions of the rudder flight control system are independent of the aileron flight control system.

Meteorological information

The recorded surface weather observations at the Toledo Express Airport about 18 minutes prior to the incident were "sky condition 700 feet scattered, ceiling 1,700 feet broken, visibility 10 statute miles, temperature 67 degrees F, dewpoint 66 degrees F, wind 300 degrees at eight knots, altimeter setting 29.88 inches."

Flight recorders

The digital flight data recorder (DFDR), a Lockheed Aircraft Services (LAS) model 209, was removed from N870BX after the incident. The recorder was sent to the Safety Boards's Flight Recorder Laboratory in Washington, D.C., where a readout and an evaluation were conducted. A report of the evaluation is attached.

According to the specialist who performed the evaluation, readout of the DFDR tape was completed with appreciable data loss; however, several parameters of interest were found to have recorded nonsensical data. The data were considered erroneous, and the afflicted parameters were not readout.

According to the specialist's factual report of the DFDR, "Observation of the available data was inconclusive regarding excessive heading change or roll rates."

Tests and research

A section of the separated aileron cable was examined at the Safety Board's Metallurgical Laboratory in Washington, D.C. A metallurgist factual report of the examination was prepared and is attached. Examination of the cable separation disclosed extensive wear along its outer diameter strands as well as between strands and individual wire elements. At the separation most of the wire elements were no longer round in shape, but instead were flat sided. In some wire elements, the flat side came to a knife edge. High magnification examination of the separation breaks with the aid of a scanning electric microscope disclosed that some of the breaks were ". . . typical of overstress separations. The wear was so severe that many wires were broken apart by the wear alone." No evidence of corrosion was found on the cable.

An examination of the wire section that did not travel in the vicinity of the pulley showed various degrees of wear, but the wear "was not severe enough to cause extensive wire separations."

The aileron power control valve and actuating cylinder were examined and functionally tested under the supervision of the Safety Board at Aircraft Systems, Miami, Florida. Visual inspection of the entire unit "revealed normal in service use, with no signs of external leakage noted." The testing revealed the valve was bypassing excessive amounts of fluid by the piston. Functional testing also revealed erratic flow indications.

According to operator records, the aileron power control valve and actuating cylinder had logged 4,678 hours since its last overhaul.

The rudder hydraulic power pack actuator shaft was examined at the Safety Board's Metallurgical laboratory. The shaft was fractured through a hole for a pin, and the pin contained a crosspin that was sheared on each side of the pin. Separation of the shaft was "typical of overstress separation, and the crosspin shearing was as if the pin rotated relative to the crosspin."

The rudder hydraulic power actuator was examined and functionally tested under the supervision of the Safety Board at Ryder Airline Services, Inc., Miami, Florida. The inspection revealed some tolerances out of limits; however, an FAA Aviation Safety Inspector reported "At the completion of the tests, it was determined that the actuator would have operated in the aircraft, either in the autopilot, or manual mode."

According to operator records, N870BX's rudder hydraulic power actuator had accumulated 46,930 hours of total time, and 16,404 hours since its last overhaul prior to fracturing.

Additional information

Maintenance Inspection Procedures.

The inspection of the aileron bus cables and control system is recommended during the "C" check and involves examining the cables for security, wear, fraying, proper tension, proper rigging, corrosion or broken wires in accordance with the operator's DC-8 Maintenance and Inspection Program manuals. In addition, the Douglas Aircraft Company recommends that "at each regular inspection, all cables fairleads, pulleys, and seals should be inspected for wear and damage." The manual also recommends inspecting the pulleys for excessive play and thoroughly checking cables over pulleys or around drums. According to the Douglas Aircraft DC-8 maintenance manual:

"Any 7 x 19 control cable which contains more that six broken wires within 1 inch of cable should be replaced. Any 7 x 19 cable worn to the point that material reduction at any cross section is equivalent to, or in excess of the area of six wires should be replaced."

Notification of the Incident.

The Safety Board was not initially notified of the incident by the operator