Peach Springs, AZ, USA
N99AT
Cessna 402A
The right main landing gear collapsed during the landing roll. The pilot placed the landing gear in the down position on downwind and noted three green lights, which indicated that the gear was down and locked. He noted a left crosswind, and landed on the left main landing gear first and then the right main landing gear. When the right main landing gear touched the ground, it folded up, and the airplane departed the runway. The airplane went over a berm, which sheared off the left main landing gear and the nose landing gear. The passengers safely deplaned. A pilot in another company airplane about 1 mile behind and 1,000 feet above the accident airplane observed the landing. He indicated that the approach and landing appeared normal. According to the Federal Aviation Administration inspector who inspected the accident scene, the airplane touched down near the threshold. There were two propeller strikes on the runway about 15 inches apart about 40 feet past the touchdown point. About 200 feet farther down the runway, there were multiple propeller strikes. The area between the first set of propeller strikes and the second set was clear of any marks. The inspector observed skid marks that began at the second set of propeller strikes and continued down the runway where the airplane departed the runway. The airplane had flown 2 hours since a routine maintenance inspection that included many components of the landing gear system. No discrepancies were noted on the failed components of the right main landing gear. Post accident inspection by the operator's maintenance personnel found that the pivot bolt in the right main landing gear bellcrank assembly (part number NAS 464P4-26) had sheared in two places, and the clevis ears at both ends of the bell crank were fractured. They said that this lead to other parts shifting and breaking, which lead to the right main landing gear collapsing. Metallurgical examination of the bell crank, the clevis ears, and the bolt determined that all of the materials examined were within specification. None of the fractures showed any evidence of pre-existing damage or fatigue cracking. The bolt fractured in shear overstress on a plane flush with the edge of the bellcrank. The damage to the pivot bolt appeared to be most consistent with an event where the gear was heavily loaded outward, away from its normal retracted position. Detailed analysis of the loadings on the failed components and the lack of damage on the surrounding structures and landing gear parts revealed no obvious scenario that would have led to the bellcrank being the first component loaded sufficiently to cause the damage observed and/or initiate the collapse of the landing gear. It is most likely that the damage to the bellcrank was a result of the collapse of the gear, rather than a cause.
HISTORY OF FLIGHT On March 9, 2004, at 1025 Pacific standard time, a Cessna 402A, N99AT, slid off runway 17 after the right main landing gear collapsed during the landing roll at the Grand Canyon West Airport (1G4), Peach Springs, Arizona. King Airlines, Inc., owned and operated the airplane under the provisions of 14 CFR Part 135. The airplane sustained substantial damage. The commercial pilot and nine passengers were not injured. Visual meteorological conditions prevailed for the sightseeing tour of the Grand Canyon, and a company visual flight rules (VFR) flight plan had been filed. The flight departed Henderson, Nevada, at 0930, and was scheduled to terminate at 1G4. The operator submitted a written report. The pilot reported that he placed the landing gear in the down position on downwind and noted three green lights, which indicated that the gear was down and locked. The three green lights were still illuminated on final. He noted a left crosswind, and landed on the left main first and then the right main. When the right main gear touched the ground, it folded up, and the airplane departed the runway. The airplane crossed a berm, which sheared off the left main landing gear and the nose gear. The passengers safely deplaned. A pilot in another company airplane about 1 mile behind and 1,000 feet above the accident airplane observed the landing. He indicated that the approach and landing appeared normal. Shortly after the airplane touched down, it turned sideways, slid down the runway, and hit a berm. A Federal Aviation Administration (FAA) inspector interviewed the pilot. The pilot stated that the landing was normal. On the landing rollout the right main landing gear collapsed and the airplane slid about 200 feet, went off the runway, and collided with a berm. AIRCRAFT INFORMATION A review of maintenance records revealed that the airplane was on an approved continuous airworthiness inspection program. The operator completed a number 4 inspection the day before the accident. The inspection report and the corrective actions noted a number of discrepancies with the landing gear, which are detailed in the following paragraphs. The airplane had flown 2 hours since this inspection. Left Main Gear The inspection noted that the left torque links had excessive play; the left gear drag leg also had excessive play. Maintenance personnel rebushed the torque links. The left gear uplock hooks didn't engage well, so technicians adjusted them. The left main gear did not retract fully; it was hanging too low in the wheel well. They adjusted the left gear fork bolt and serviced it. The left gear door uplock tension was 0 pounds, and they adjusted the up limit switch to obtain proper tension. The manufacturer reported that the down lock tension should be 40 to 50 pounds during rigging, and 40 to 60 pounds during an in-service inspection. The left gear outboard drive tube was bent; they installed and secured a serviceable drive tube. Right Main Gear The right torque links had excessive play; technicians rebushed the torque links. They noted that the right gear door uplock tension was 0 pounds, and it was not hitting the stop. They adjusted the up limit switch as required. They noted that the right gear downlock tension was 90 pounds, and adjusted it to 50 pounds. Nose Gear The nose landing gear uplock tension was 45 pounds; technicians adjusted it to 72 pounds. The nose gear door hinge pins were working out of the hinges; they secured the pins. The nose gear downlock tension was 10 pounds, and they adjusted it to 23 pounds. The nose gear uplock hook was not properly adjusted; they adjusted the hook and serviced it. The gear down limit switch was not properly adjusted (it was four cranks to the stop); technicians adjusted it to a two-crank position. They also rigged and lubricated all of the landing gear. WRECKAGE AND IMPACT According to the FAA inspector, who inspected the accident scene, the airplane touched down near the threshold. There were two propeller strikes on the runway about 15 inches apart about 40 feet past the touchdown point. He stated that about 200 feet farther down the runway, there were multiple propeller strikes. The area between the first set of propeller strikes and the second set was clear of any additional marks. The inspector observed skid marks down the runway where the airplane departed the runway. The airplane went over a berm, which sheared off the left main landing gear and the nose landing gear. The airplane came to rest on its belly. The right side of the vertical stabilizer had a hole in it, and the right wing tip tank ruptured. TESTS AND RESEARCH Post accident inspection by maintenance personnel from the operator reported that the head of a bolt in the right bellcrank assembly (part number NAS 464P4-26) sheared off. They said that this allowed the bellcrank assembly (part number 5041001-10) to shift in its assembly. This broke the upper lug that supported the bellcrank, which released the downlock pressure. The lower end of the assembly also broke at the end of the lock support. The side brace went over center in the retracted position. Metallurgical Examination The National Transportation Safety Board investigator-in-charge (IIC) submitted the right main landing gear retraction bellcrank to the Safety Board Material's Laboratory for examination. A specialist prepared a factual report, which is attached. Pertinent parts of the report follow. The forward ear of the lower clevis fitting broke off, as did the head end of the pivot bolt. The upper clevis was undamaged. The forward ear of the clevis fractured in bending overstress, with the ear of the clevis bent forward with respect to the body of the bellcrank, as indicated by residual permanent deformation adjacent to the fracture surface. The aft ear of the clevis had three small gouges on the interior surface, but no other deformation or damage. The specialist said that this indicated that it had been highly loaded. The specialist stated that the bolt fractured in shear overstress on a plane flush with the edge of the bellcrank. Residual permanent deformation of the bolt adjacent to the fracture and the bushing surrounding the bolt indicated that the fracture occurred as a result of motion of the bellcrank directly inboard with respect to the landing gear trunnion, assuming that the landing gear was fully extended. The threaded end of the bolt also showed evidence of similar residual permanent shearing deformation in the same direction, indicating that the bolt was highly loaded in shear at both ends. The bellcrank was part number 0841220-4. X-ray energy dispersion spectroscopy (EDS) of the bellcrank in the scanning electron microscope identified a major peak for aluminum and minor peaks for copper, silicon, manganese and magnesium, consistent with the specified aluminum alloy. Additional minor peaks for iron, oxygen, and carbon were also identified in some areas. Rockwell B hardness (HRB) measurements on the bellcrank averaged 82 HRB. Converting from the Rockwell B measurement to the Brinell scale, the bellcrank hardness averaged 135 HB (500 kg load, 10 mm ball). Electrical conductivity measurements on the bellcrank averaged 38.5 percent IACS. The pivot bolt was specified to be NAS464P4, indicating a 0.25-inch diameter steel bolt with a cotter pin hole and cadmium plating on the entire bolt, as per National Aerospace Standard 464. The standard indicated that the heat treatment of the bolt should lead to a tensile strength between 160 ksi (kilopounds per square inch) and 180 ksi. Measurements of the bolt diameter averaged 0.2481 inch. X-ray EDS of the fracture surface of the bolt identified a major peak for iron and minor peaks for manganese, silicon, and carbon. X-ray EDS of the lateral surface of the bolt also identified a major peak for iron and minor peaks for manganese, silicon, and carbon in similar proportions, along with a peak for cadmium consistent with a cadmium plating. Hardness measurements on the bolt averaged 39 HRC, which correlates to a tensile strength of 177 ksi.
the pilot's inadequate flare and touchdown that imparted high side loadings on the right main landing gear, which resulted in an overload failure of the landing gear bellcrank and the collapse of that gear.
Source: NTSB Aviation Accident Database
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