Anchorage, AK, USA
N5760D
Piper PA-18-150
The private pilot reported he made a hard landing on a paved runway in his tail wheel and tundra tire equipped airplane, and that the left main landing gear assembly subsequently collapsed. The airplane sustained structural damage to the left wing when it struck the runway. An inspection of the main landing gear (MLG) assembly by the NTSB investigator-in-charge and FAA certification engineers, disclosed that the MLG was not an approved component, although it had been stamped "PMA" for Primary Manufacturing Authority, indicating it was an approved part. Further research and analysis of the gear assembly revealed that it had fractured at the shock strut attachment lugs, and that the lugs were approximately one-half strength of the original factory equipment. The MLG assembly has been available for several years, and may be retro-fitted to the entire Piper Cub series airplanes. The FAA aircraft certification branch and the manufacturer are presently conducting a review of the design and have indicated that a manufacturer's Service Bulletin will be published offering a strengthened version of the MLG, and that the FAA will issue either a Special Airworthiness Information Bulletin, or an Airworthiness Directive.
On October 7, 2004, about 1730 Alaska daylight time, a tundra tire-equipped Piper PA-18-150 airplane, N5760D, sustained substantial damage during a hard landing and subsequent collapse of the left main landing gear while landing at Merrill Field, Anchorage, Alaska. The private pilot/airplane owner and the sole passenger were not injured. The Title 14, CFR Part 91 personal flight originated at Kenai, Alaska, about 1610, and the destination was Anchorage. Visual meteorological conditions prevailed, and no flight plan was filed. The pilot reported in his written statement to the NTSB investigator-in-charge (IIC) that he was landing on runway 33, and flared too high, about 8 to 10 feet above the runway. The airplane subsequently stalled, and "dropped in." The left main landing gear collapsed on touchdown, and the left wing struck the runway. The pilot also noted in his written report that: "Pilot awareness is the key to prohibiting future incidents." He indicated that the airplane had no preaccident mechanical problems, that it was approved for use with over-sized tires, and that it was operating at near gross weight. The NTSB IIC examined the airplane and discovered structural damage to the two outer ribs on the left wing. An inspection of the left main gear assembly by the NTSB IIC disclosed that the original equipment manufactured (OEM) main landing gear (MLG) had been replaced by an assembly manufactured by F. Atlee Dodge Aircraft Services, of Anchorage. The Dodge MLG assembly on the accident airplane, Dodge part number 3165L, had fractured at the shock strut attachment lugs. An inspection of the fracture surfaces disclosed fracture surfaces consistent with overload failure. The pilot of the accident airplane provided an older, OEM type gear leg for comparison, and it was noted that the older MLG assembly strut attachment tabs were considerably thicker and wider than the Dodge tabs. The NTSB IIC requested assistance from the Anchorage FAA Aircraft Certification Office in evaluating the design strength of the Dodge MLG strut tabs, and reviewing any supplemental type certificate (STC) or primary manufacturing authorization (PMA) that had been submitted to the FAA certification branch by Dodge for approval. According to the two FAA aerospace engineers who were assigned to assist in the investigation and review of the Dodge MLG, Dodge had not been issued an STC or a PMA for the MLG assembly, even though the gear assembly had been stamped by Dodge "PMA." They noted that Dodge has recently applied for both an STC and PMA for an improved, stronger version of the MLG assembly. The FAA engineers indicated that their calculations determined that the accident MLG assembly was approximately 50 % weaker than the OEM MLG, and may be below the original certification standards that were in place when the airplane was certificated. The Anchorage FAA certification office is presently working with Dodge in determining how many gear assemblies for the Piper Cub series airplanes (J-3, PA-11, 12, 14, 18 and 19) airplanes have been distributed, and over what time period. The manufacturer was unable to state exactly when he started producing the accident MLG, but that it has been in production for several years. The certification office has requested that the manufacturer issue a Service Bulletin for the gear assembly, and, in addition, the FAA will issue either an Airworthiness Directive or a Special Airworthiness Information Bulletin, predicated upon further testing of the currently unapproved gear leg.
The inadequate and unapproved design of the main landing gear assembly by the manufacturer, which resulted in a failure of the main landing gear during landing, and structural damage to the airplane. A factor in the accident was the pilot's misjudged flare.
Source: NTSB Aviation Accident Database
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