CHARLOTTE, NC, USA
N865US
Fokker F100
The Fokker F100 was on landing rollout when the right main landing gear collapsed. Review of company maintenance records revealed the torque link damper on the right main landing gear was serviced using a company maintenance task/job card. The procedures did not follow the maintenance procedures listed in the aircraft manufacturer's maintenance manual, and the required tools (replenishing gun) was not available to service the torque link damper assembly. Examination of the failed components by the NTSB Materials Laboratory Division revealed fractures from the main fitting had a chevron pattern caused by overstress originated at the base of the upper torque link attach lug. No preexisting cracks were noted.
HISTORY OF FLIGHT On November 7, 1997, about 1017 eastern standard time, a Fokker F100, N865US, flight 479, registered to and operated by US Airways, as 14 CFR Part 121 scheduled domestic passenger flight, from Milwaukee, Wisconsin, to Charlotte, North Carolina, experienced a failure and separation of the right main landing gear on landing rollout at the Charlotte-Douglas International Airport. Visual meteorological conditions prevailed and an IFR flight plan was filed. The airplane sustained substantial damage. The airline transport-rated pilot-in-command, first officer, 3 flight attendants, and 99 passengers reported no injuries. The flight originated 1 hour 57 minutes before the accident. The PIC stated the first officer made the approach and landing to runway 36 left. On landing rollout the airplane experienced a slight vibration which increased in intensity rapidly. The PIC effected a positive change of controls and instructed the first officer to notify the control tower that they would stop on the runway and to dispatch the emergency vehicles. The airplane started to veer to the right. Differential braking, rudder pedal steering, and nose wheel steering was used to keep the airplane aligned with the centerline of the runway. The airplane came to a complete stop. The first officer informed the PIC that the right wing was resting on the runway. The emergency passenger evacuation checklist was initiated and an evacuation of the airplane was commanded. All passengers and crew evacuated the airplane utilizing the forward galley service door, down the emergency escape chute, or through the right over wing emergency exits. The flight attendants stated the evacuation was calm and orderly except for passengers delaying evacuation while trying to retrieve carry-on bags. A left main landing gear brake fire was extinguished by company maintenance personnel. PERSONNEL INFORMATION All pertinent aviation regulations, 14 CFR Part 121, airman competency and proficiency checks, had been recorded as conducted. Further information pertaining to the pilot-in-command is contained in this report on page 3 First Pilot Information, NTSB Form 6120.4 Supplement U, CFR 121 Training and Flight Checks, and NTSB Form 6120.1/2 Pilot Information. All pertinent aviation regulations, 14 CFR Part 121, airman competency and proficiency checks have been recorded as conducted. Further information pertaining to the first officer is contained in NTSB Form 6120.1/2, Second Pilot Information, and NTSB Form 6120.4, Supplement E, Second Pilot Information, and Supplement U, 121 Training and Flight Checks. All pertinent aviation regulations, 14 CFR Part 121 flight attendant competency and proficiency checks have been recorded as conducted. Further information pertaining to the flight attendants is contained in NTSB Form 6120.4, Supplement U, Flight Attendant Information. AIRCRAFT INFORMATION Review of maintenance records revealed the right main landing gear (RMLG) had 13,890.5 hours and 13,108 cycles at the time of the accident, and had never been overhauled, only repaired. The heavy check (overhaul) on the RMLG was not due until 18,500 hours. The shimmy damper installed on this aircraft is MAL-095. The RMLG was initially installed on N883US. It was declared unserviceable on July 18, 1996, due to a reported gear vibration and worn bushings in the torque link. The RMLG was sent to a U.S. Airways landing gear shop at Winston-Salem for repair. The upper torque link, torque link pin, torque link apex pin, and shimmy damper unit were replaced. The main fitting torque link bore dimensions were found to be within the original size of 2.1562 to 2.1580 inches inside diameter per the component maintenance manual 32-10-62 repair #6; however, there was no record of the dimensions in the repair document, and replacement bushings were fabricated. The inside diameter of the bushings were honed to ensure the upper torque link pin would be installed with the required interference fit. The RMLG was declared serviceable on July 18, 1996, and placed in the Pittsburgh (PIT) inventory. The RMLG was declared unserviceable on January 27, 1997, after the upper torque link, torque link pin, shimmy damper, and apex pin were robbed, and placed on another airplane. The RMLG was returned to Winston-Salem to have the robbed parts replaced. A visual check of the main fitting upper torque link attach lug bushings revealed the inner diameter of a lug bushing and two antirotation pin bushings had been scored when the component was robbed. The main fitting torque link lug dimensions were within limits, and replacement bushings were fabricated. The RMLG was placed back in serviceable condition on January 29, 1997, and installed on N865US on February 5, 1997. For additional information see NTSB Maintenance Records Group Chairman Factual Report and Aircraft Information contained in NTSB Form 6120.4. A review of logbook pages concerning the RMLG from September 22, 1997, and 1 week before the accident revealed the following write ups and corrective action: October 8, 1997 Hydraulic fluid was dripping between the wheels of the right gear. Action Found brake line inboard "B" nut loose. Tightened "B" nut on the # 3 brake shuttle valve. Cycled brakes several times. October 9, 1997 The # 2 RMLG shimmy damper is leaking. Action Serviced shimmy damper in accordance with Maintenance Manual task 12-12-02-610-813A. October 10, 1997 The RMLG shimmy damper requires servicing frequently. Action The shimmy damper was serviced per U.S. Airways Job Card 532-11-0. Note: the damper was programmed for replacement at the next overnight Transit Check. October 14, 1997 The RMLG shimmy damper checked normal. No leaks were noted, and there was no history listed in the maintenance data computer system. Action None. October 28, 1997 Nose gear strut bumps, grinds, and bottoms-out during taxi. Action Serviced strut per J5-90-0007C-001 procedures. METEOROLOGICAL INFORMATION Visual meteorological conditions prevailed at the time of the accident. For additional information see pages 3 and 4 of this report, Weather Information. FLIGHT RECORDERS N865US was equipped with a Fairchild model A100 cockpit voice recorder. The recorder was forwarded to the NTSB laboratory for analysis. The cockpit voice recorder was recorded clearly. The recording indicated no abnormal operations by the flight crew. No transcript of recorded communications was made. N865US was equipped with a Loral model F800 digital flight data recorder (DFDR). The recorder was forwarded to the NTSB laboratory for analysis and a successful readout was performed. The DFDR indicates the airplane made a normal descent and landing to runway 36 left at an airspeed of 133 knots. The vertical acceleration shows increased activity after touchdown and the data indicates a change in roll from 0 degrees to 2 degrees. The roll registers 2 degrees for 3 seconds, at which point the maximum vertical acceleration of 1.41gs is measured. Immediately following, the roll increases to almost 12 degrees, and the airplane comes to rest on a heading of 016 degrees. (For additional information see NTSB Flight Data Recorder Specialist's Factual Report of Investigation.) WRECKAGE AND IMPACT INFORMATION N865US was located on runway 36 left, 5,903 feet from the landing threshold on a heading of 016 degrees magnetic. Examination of the runway revealed evidence of faint shimmying of the No. 3 right main landing gear wheel 2, 750 feet from the landing threshold. Additional shimmying indications (tire marks) from the Nos. 3 and 4 main wheel assemblies were noted 2,920 feet from the threshold. The first indication of hydraulic fluid was noted on the runway 3,274 feet from the threshold. A consistent heavy accumulation of hydraulic fluid extended in a straight line masking the tire marks on the runway for an additional 500 feet. The right wing tip collided with the runway 3,773 feet from the threshold, and the right main landing gear fitting struck the runway 3,800 feet from the threshold. Scarring marks from the upper part of the landing gear main fitting assembly were present on the runway, and were overlapped by consistent dark rubber tire marks from the right main landing gear. The tire marks were located aft of the dragging strut, and continued in a straight line until the airplane veered to the right and came to a complete stop. Components that separated from the landing gear were found 4,570 feet from the threshold, scattered on both sides of the centerline and extended down the runway for the next 1,333 feet. The following components were located on the runway: Shimmy damper reservoir. Pieces of the right main landing gear fitting. Right main landing gear fitting inner steel sleeve. Pieces of the upper bearing split housing. Ground/flight sensor bracket assembly. A piece of the landing gear data plate. Part of the inboard flap upper skin surface. Further examination revealed tire marks were located several feet to the outside of the landing gear main fitting. The lower landing gear assembly was trapped by the inboard flap and dragged behind the broken main fitting. The lower landing gear assembly separated, bounced, and struck the right engine inlet cowling at the 5 o'clock position. The lower landing gear sliding member assembly was located about 47 feet forward of the right wing tip. Examination of the Nos. 3 and 4 tires and brake assemblies revealed no deficiencies. Examination of the airframe and flight control assembly revealed no evidence of a precrash mechanical failure or malfunction. All components necessary for flight were present. Continuity of the flight control assembly was confirmed for pitch, roll, and yaw. There was evidence of minor fire damage (sooting) to the left main landing gear assembly, on the strut, brakes, and tires. An engine examination/disassembly was not conducted. Examination of the interior cabin revealed no damage or deficiencies with the emergency exits. Flightcrew seats, flight attendant jumpseats, and passenger seats including restraint systems, revealed no evidence of damage or malfunction. MEDICAL AND PATHOLOGICAL INFORMATION Toxicology studies of specimens from the PIC, first officer, and flight attendants were performed by American Medical Laboratories Inc., Chattily, Virginia. These studies were negative for alcohol, basic, acidic, and neutral drugs. The testing of the specimen for the B position flight attendant was not conducted. The specimen leaked during shipment and there was an insufficient amount of sample for the required test. TEST AND RESEARCH A bench test was conducted on shimmy damper serial number MAL-780, utilizing U.S. Airways Job Card J532-11-0, dated December 4, 1997. The job card contained two pages of text without graphics. The procedure requires the use of dispenser tool number T601203, and a replenishing gun. The dispenser could not be used while following step 2 of the required procedure. The tool was not equipped with a needle valve or bleed hose. The maintenance procedure listed in the Fokker Maintenance Manual for task 12-12-02-610-813A, view c, located on page 305 was printed. The fill and bleed hose assembly was different from the hose assembly T601203 provided by the U.S. Airways Job Card. Telephonic communication with the stock rooms located at Winston-Salem, Charlotte, company personnel, and Fokker Services personnel at Pittsburgh, revealed they had the same tool required by the job card. The alternate procedure in the Fokker Maintenance Manual Task 12-12-02-610-823A, Torque Link Damper Servicing, located on page 301-306, was used and completed with ease. U.S. Airways issued numerous revisions to task card/job card (J532-11-0). The card was unclear and listed an incorrect dispensing tool that was unusable. (See addendum to the maintenance records Group Chairman's Factual Report). U.S. Airways issued a revision of Job Card J532-11-0 on December 4, 1997, pertaining to the servicing of the Main Landing Gear Torque Link Damper Check and Service, and a Maintenance Alert Bulletin was issued on December 12, 1997. Fokker Services deleted Fokker Services Maintenance Manual Task 12-12-02-610-813A from the U.S. Airways customized version of the Fokker Maintenance Manual. The alternate procedure, Task 12-12-02-610-823A, has been revised and was republished as Task 12-12-02-610-833A and was included in the June 1998 Fokker 100 Maintenance Manual revision for US Airways, (external leakage). Static testing of the RMLG shimmy damper was conducted in Oakville, Ontario, Canada, at Menasco Aerospace. The unit was tested and disassembled to verify its integrity. A visual inspection of the unit was performed and showed no evidence of black grit (brake/tire dust). The threads of the damper housing sheared off as a result of impact loads, and was not caused by over-pressurizing of the unit. A reservoir subassembly leakage and relief pressure test was performed on a hydraulic stand, and the unit functioned normally. Due to extensive damage to the boss face, an inadequate seal support did not allow a test of the damper subassembly. The reservoir assembly was tested for two procedures and all tests were completed satisfactory except for 1. B (4). The damper was disassembled to verify the unit had been assembled correctly. The disassembly determined that it had been assembled correctly. The disassembly of the reservoir assembly determined no deficiencies with the internal components. The assemblies were reassembled with the Component Maintenance Manual, and were shipped to the NTSB in Miami, Florida. The units were subsequently shipped to the Netherlands Aviation Safety Board for dynamic testing at National Aerospace Laboratory (NLR) located in Amsterdam, Holland. The excitation tests included MAL-095 with various damper configurations, and a verification damper for reference. For additional information see Menasco Aerospace Shimmy Damper Investigation Reference No. SE2473-97, Fokker Services report No. TE-0169, and NTSB Structures and Systems Group Chairman's Factual Report. Examination of the RMLG Antiskid Control Valve was conducted in Akron, Ohio. Visual examination revealed no evidence of external damage. It was noted that the first stage valves were the original configuration, and not the latest configuration. The inboard and outboard valves failed the hydraulic test, and a complete functional test was performed. It was concluded that the valve condition would not have an effect on the normal non-antiskid braking. For additional information see NTSB Structures and Systems Group Chairman Factual Report. Examination of RMLG components including fragments from the main fitting P/N 201072384, S/N LOE250, the upper torque link, and the upper torque link pin and pin attachment bolt was conducted by the NTSB Materials Laboratory Division. Visual examination of fractures from the main fitting revealed a chevron pattern caused by overstress originated at the base of the upper torque link attach lug. No preexisting cracks were noted. Scanning electron microscope examination of fracture samples, excised from origin fragment, revealed no fatigue striations or crack arrest marks. No corrosion damage was found on the inside or outside diameter surface. The upper torque link contained no cracks or fractures. For additional information see NTSB Materials Laboratory Factual Report No. 98-62. ADDITIONAL INFORMATION The airplane was released to Captain George H. Snyder, Vice President, Corporate Safety and Regulatory Compliance, U.S. Airways Inc., on November 10, 1997. The cockpit voice recorder was released to Mr. Homer G. Huie, Manager, Stock Distribution/Transportation and Customs, U.S. Airways Inc., on November 17, 1997. The digital flight data recorder was released to Mr. Homer G. Huie, on December 4, 1997. Fragments from the main fitting P/N 201072384, S/N LOE250, one metallurgical mount, two bushings, the upper torque link, the upper torque link pin and pin attach bolt, for the right main landing gear, were released to Mr. Homer G. Huie on April 13, 1998. Additional parties to the NTSB investigation were Mr. Michael E. Gard
Improper written instructions (job/task card) by company maintenance personnel. The procedures did not reflect the correct manufactures maintenance manual servicing procedure, and did not ensure that the proper tool (replenishing gun) was available for the servicing of the torque link damper. This resulted in the improper servicing of the damper, and subsequent collapse of the right main landing gear on landing rollout.
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