Chattanooga, TN, USA
N829AS
Canadair CL-600-2B19
After takeoff the flight crew heard a high frequency vibration which could be felt in the feet and control column. The engine indicating and alerting system indicated no messages. The vibration was slow and increased in intensity and lasted about 30 seconds. The flight was cleared to 17,000 feet, and the airplane started an uncommanded roll to the right. The first officer disconnected the autopilot and regained control of the airplane. The captain declared an emergency, and was issued a clearance to an alternate airport. The vibrations continued at all airspeeds during the descent and landing. Examination of the airplane revealed the bushings and right aileron inboard and outboard power control unit output link were worn and exceeded the authorized tolerance allowed by the maintenance manual. The aircraft manufacturers inspection procedures for the aileron system backlash check did not require the operator to record the tolerance found during the backlash check.
HISTORY OF FLIGHT On May 8, 2003, at 1228 eastern daylight time, a Canadair CL-600-2B19, N829AS, Flight 4690, registered to State Street Bank Company of Connecticut, and operated by Atlantic Southeast Airlines, Inc., as a 14 CFR Part 121 scheduled domestic/international passenger flight, diverted to Chattanooga, Tennessee, after an uncommanded roll during cruise climb. Visual meteorological conditions prevailed and an instrument flight rules flight plan was filed. The airplane was not damaged. The airline transport rated captain, commercial pilot rated first officer, one flight attendant, and 18 passengers reported no injuries. The flight departed Atlanta, Georgia, at 1219 on May 8, 2003, en route to Montreal, Canada. After liftoff, the first officer, who was flying the airplane, felt and experienced a high-frequency vibration. The vibration could be felt in his feet and the control column. The engine indicating and crew alerting system (EICAS) indicated no messages. When the airspeed was increased to 250 knots, the vibration started again. The vibration was slow and increased in intensity. The captain contacted company maintenance while the first officer engaged the autopilot. The vibrations continued and lasted about 30 seconds. When the flight was cleared to 17,000 feet, the airplane started an uncommanded 45-degree roll to the right. The first officer disconnected the autopilot and regained control of the airplane. The captain declared an emergency, and was issued radar vectors to Chattanooga. The first officer initiated a power off descent while the captain monitored the instruments and the synoptic pages. The vibrations continued at all airspeeds during the decent and landing. Review of radar data revealed the airplane deviated to the right while climbing through 15,200 feet at 1228:40. The airplane deviated to the right again at 1229 climbing through 15,500 feet. At 1229:20, the airplane deviated to the right while climbing through 15,900 feet. The airplane deviated to the right at 1230 while climbing through 16,500 feet. The last deviation to the right was at 1230:31 at 17,100 feet. PERSONNEL INFORMATION Review of information on file with the FAA Airman's Certification Division, Oklahoma City, Oklahoma, revealed the airline transport rated pilot-in-command was issued an airline transport pilot rating on January 23, 2002, with ratings for airplane single engine land, multiengine land and instrument airplane. In addition the pilot was issued a flight instructor certificate on Feb 9,1998, with ratings for airplane single engine land and instrument airplane. The pilot was hired by Atlantic Southeast Airlines, Inc, on September 9, 1998. The pilot was type rated in the EMB 120 on April 13, 2000, and was type rated in the CL65 on January 23, 2002. The pilot was qualified as a CL65 captain on January 23, 2002. The last recorded line check was on December 31, 2002.The pilot's last recurrent ground training was conducted on December 13, 2002, through December 19, 2002. The pilots last proficiency check ride/biennial flight review was completed on June 17, 2002. The pilot has 1,053 total hours in the CL65.The pilot held a first class medical certificate issued on December 9, 2002, with the limitation must wear corrective lenses. Review of information on file with the FAA Airman's Certification Division, Oklahoma City, Oklahoma, revealed the commercial pilot, first officer, was issued a commercial pilot certificate on September 5, 2000, with ratings for airplane single engine land, multiengine land and instrument airplane. Atlantic Southeast Airlines hired the pilot on January 29, 2001. The pilot was qualified as a CL65 first officer on April 14, 2001.The pilots last proficiency check ride/biennial flight review was completed March 5, 2003. The pilots last recurrent ground training was conducted on April 8, 2003, through April 10, 2003. The pilot has 1,027 total hours in the CL65. The pilot held a first class medical issued on December 18, 2002 with no restrictions. Review of Atlantic Southeast Airlines, Inc, records revealed the flight attendant successfully completed initial flight attendant training on September 5, 2001, and completed recurrent training on September 19, 2002. The flight attendant was current and qualified. AIRCRAFT INFORMATION Review of aircraft maintenance records revealed the last "A" check was conducted on April 14, 2003. The "C1" check was conducted on March 10, 2002 and required the functional check and backlash check of the aileron control system. No anomalies were noted during the inspection. The last routine service 100-hour/10 day checks was conducted on May 5, 2003. The airframe had 13,127.40 hours and 11,917 cycles on May 8, 2003. The left engine was installed on April 13, 2003. The total time since new was 6,417.6 hours and 131.5 hours since overhaul. The left engine cycles since new was 6,323 hours. The right engine time since new was 6,541.5 hours and 2,883.0 hours since overhaul. METEOROLOGICAL INFORMATION The nearest weather reporting facility at the time of the incident was Chattanooga, Tennessee. The 1653 surface weather observation was: 1,500 broken, visibility 6 miles, temperature 75 degrees Fahrenheit, dew point temperature 69 degrees Fahrenheit, wind variable at 4 knots, and altimeter 30.05. WRECKAGE AND IMPACT INFORMATION The NTSB Systems Group met at Lovell Field, Chattanooga, Tennessee, to document the airplane and relevant systems. The airframe, auto flight, electrical power, and flight control systems were examined. No anomalies were noted with the airframe, auto flight, and electrical power. The lateral control system was exercised via the captain's and first officer's control wheels. No anomalies were noted in the captain's control wheel movement. A slight notching was noted in the first officer's control wheel movement. When the captain's control wheel was used to exercise the first officer's lateral control system, no notching was noted. Hand movement of the right aileron control surface indicated free play within the system. The travel of the trailing edge of the right aileron from a pushed-down position to a pushed-up position was measured as 7/16", with the hydraulic systems turned off. The travel of the trailing edge of the left aileron from a pushed-down position to a pushed-up position was measured as 1/4". The under wing aileron access panel on the right wing was removed for a visual inspection of the two aileron output linkage connection to the aileron. When the right aileron was manually moved, free play was noted between the power control unit (PCU) output link, the aft attach bolt, and the aileron fitting. The attachment bolt could be moved by hand. The main landing gear wheel well bay fairings were removed and the aileron control quadrant pulleys were examined. No anomalies were noted in the static condition of the pulleys. When the lateral control system was exercised in the flight deck, no anomalies were noted in the operation of the pulley and cable movement. Visual inspection of the aileron flight control cables under the cockpit floor revealed no anomalies were noted. The right under wing aileron PCU access panel was removed and the two aileron PCUs were examined. No anomalies were noted. The over wing aileron access panel was removed on both wings. The outboard aileron pulley was examined on both wings. The outboard aileron pulley on the right wing did not rotate freely and required a higher than normal torque to rotate the pulley. An aileron control system-backlash check and functional test was performed on the airplane's left and right ailerons in accordance with airline task card 019-27-900-709. The test was altered so only the portions of the test pertaining to the outboard aileron PCU were accomplished. The test on the right outboard PCU, right aileron bearing, and left aileron PCU were accomplished twice, while the left aileron-bearing test was accomplished once. The results of the tests were: Right Aileron PCU Check 1st Test: 0.370" Backlash 2nd Test: 0.370" Backlash Right Aileron Bearing Check 1st Test: 0.130" Backlash 2nd Test: 0.140" Backlash Left Aileron PCU Check 1st Test: 0.133" Backlash 2nd Test: 0.133" Backlash Left Aileron Bearing Check 1st Test: 0.083" Backlash (only one test accomplished) The PCU test procedure indicates any backlash value greater that 0.125 inches constitutes failure of the test. Any backlash value greater than 0.070 inches for the bearing test procedure constitutes failure of the test. The left and right ailerons backlash test results were not within the prescribed limits. Components from the left and right wing aileron to PCU link for the inboard and outboard PCU, aileron bushings for the right wing for the inboard and outboard PCU, and aileron attach bolt washers were submitted to the NTSB Materials laboratory for examination. The airplane manufacturer does not retain historical fleet results from the aileron backlash test. At the time of the incident, the airplane operators were not required to provide the manufacturer with results of the test for their fleet. The measured backlash values are not recorded or retained by the operator or person executing the test. No evidence of abnormalities of the rudder, rudder trim, and yaw damper systems were noted. The trailing edge flaps and trailing edge flap selector were noted at 8-degrees. Movement and visual examination of the trailing edge flaps and associated fairing revealed no evidence of trailing edge flap anomalies. The two spoilerons were noted in the retracted or down position. The spoilerons were moved by hand and visually examined. With normal hydraulic power the gap between the trailing edge of the spoileron and the wing was measured at the hinge locations. The gap was measured as follows: Left Spoileron Inboard: 0.010" Outboard: 0.028" Right Spoileron Inboard: 0.067" Outboard: 0.105" The spoiler electronic control units (SECU) built-in test equipment (BITE) function was activated. No faults were noted on either SECU units. The flight spoilers were noted in the retracted or down position. Manual movement of the spoilers and visual inspection of the flight spoilers indicated no visible evidence of flight spoiler anomalies. The flight spoilers were activated via the flight deck control and the flight spoilers activated in a consistent manner. MEDICAL AND PATHOLOGICAL INFORMATION The airline transport rated pilot-in-command, commercial pilot first officer, flight attendant, and 18 passengers reported no injuries. No toxicology specimens were requested from the flight crew. TEST AND RESEARCH The Loral F-1000 Solid State Flight Data Recorder (FDR), was downloaded by Precision Avionics, Atlanta, Georgia, in the presence of Atlantic Southeast Airlines, Inc, and forwarded to the NTSB Chief Vehicle Recorders Division. The FDR recording contained approximately 50 hours of data. The duration of the incident recording was approximately 56 minutes, which included the ground time before and after the flight. The Fairchild Digital Cockpit Voice Recorder (CVR), model F1000 was forwarded to the NTSB Recorders Division. Examination of the CVR by the NTSB determined that the recording did not include any pertinent information. A CVR group was not formed. Examination of the components submitted to the NTSB Materials Laboratory revealed wear and polishing on many of the fraying surfaces of the components. Wear locations included the outer diameters of the bolts, both diameters of the straight bushings, the inner diameters of the flanged bushings and the balls and sockets of the links. The radial play was measured at each ball location on the four ailerons to PCU links. The engineer drawing specifies "radial free play 0.003 inch max(imum)" between each ball and link when new. At two locations the measured play was 0.0035 inch. Less play was noted on the PCU sides of the links and greater play on the aileron side for all links. Disassembly of the links found that the aileron balls and sockets showed visible wear on the spherical surfaces of the balls and sockets and the end faces of the balls. The aileron side balls were noticeably cleaner and more lustrous than the PCU side balls. The inner diameters showed some circumferential wear and in almost all instances slightly exceeded the drawing's dimensional requirements for the inner diameter. Hardness of each ball and link was also tested and in all instances the components met the hardness requirements of the engineering drawing. The aileron bushings visually exhibited wear at many locations on the link to the aileron attachment hardware. Under magnified optical examinations, the wear characteristics on the bushings appeared consistent with a galling wear mechanism. The flanged bushings were worn on the inner diameters and measured hardness values were typical of the drawing specified material and heat treatment. The straight bushing had wear marks on both the inner and outer diameters. On the outer diameter, a band was worn around the center. The wear band location and width corresponds to the installed location of the flanged bushing. Comparisons of the measured diameters indicate removal of significant amounts of material from the outer diameters and less from the inner diameters. The measured hardness was consistent with the specified material and heat treatment and also typical of the other bushings. Circumferential marks formed three distinct bands on the grip portions of the shanks of the attachment bolts indicated as bands 1, 2, and 3. Dimensional measurements found little or no reduction of the diameters of bands 1 and 2 near the bolt head. Significant material was removed from band 3 adjacent to the threads. The location of band 3 corresponds to the installed location and width of the flanged bushing. Bands 1 and 2 correspond to the installed locations of the straight bushing and link ball. ADDITIONAL INFORMATION The airplane was released to the Director Safety-Flight Operations Corporate Safety and Compliance, Atlantic Southeast Airlines, Inc, on May 11, 2003. The cockpit voice recorder was released to Atlantic Southeast Airlines, Inc, on May 9, 2003. The components retained by the NTSB for further examination were released to Atlantic Southeast Airlines on August 4, 2003.
Excessive wear on the bushings and the right aileron inboard and outboard power control unit output link resulting in the upward movement of the right aileron during cruise climb, uncommanded right roll. A factor in the accident was inadequate maintenance inspection procedure by the aircraft manufacture for the aileron system backlash check performed by the operator. The inspection procedure did not require the operator to record the tolerance found during the backlash check.
Source: NTSB Aviation Accident Database
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