CHI08LA115

The airplane's main landing gear struts were replaced with repaired struts during a maintenance inspection. The FAA Form 337 associated with the repair states that the landing gear was checked for correct contour configuration and strength, and had undergone a magnetic particle inspection, but does not cite the approved data used for the repair. The left landing gear strut separated during a hard landing about 341 hours after it had been installed. The pilot aborted the landing, and flew to another airport where the airplane landed without the left main landing gear. The horizontal stabilizer was damaged during the initial landing attempt when the left landing gear separated, and struck the horizontal stabilizer. Metallurgical examination of the landing gear showed an altered micro structural layer adjacent to the surface, indicative of excessive thermal input such as welding. The strut portion showed that most of the exterior surface contained an intact layer of white paint. In many locations throughout the strut, the paint appeared to have been applied to an irregular or pitted surface.

On April 24, 2008, at 1810 eastern daylight time, a Cessna 182, N5358B, piloted by an airline transport pilot, received substantial damage on impact with terrain during landing on runway 18 (4,000 feet by 75 feet, asphalt) at Romeo State Airport (D98), Romeo, Michigan. The pilot landed the airplane with a portion of the left main landing gear missing after it had separated at the strut during a previous landing attempt on runway 36 (2,600 feet, grass) at Kunstman Private Airport (PVT), Ray, Michigan. During the landing at PVT, the airplane touched down "somewhat hard" on the left main landing gear. The pilot aborted the landing and returned to D98. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 personal flight was not operating on a flight plan. The pilot was uninjured.

The pilot reported that he approached PVT from the southwest and flew a non-standard approach to runway 36 to avoid flying over a farm to the south. The planned touchdown point was about 1/4 down the runway in order to avoid a rise in the runway. The approach to the runway was at an indicated airspeed of about 65 mile per hour in a slight right slip. The wind was from the east with gusts. About 3 feet above the ground, the airplane lost lift and the airplane touched down in a slight crab to the right, left wing and tail low, and not too hard. The pilot heard a pop like a tire blowing and he then aborted the landing. Once airborne, he looked out the window and saw a hole in the left flap and a portion of the left landing gear missing. He then looked back and saw damage to the leading edge of the horizontal stabilizer and a portion of the elevator missing.

Examination of the runway revealed a ground scar consistent with the initial touchdown point that was about 15 feet to the left of the prepared (rolled grass) runway 36 surface. Two ground scars relating to the left main landing gear and nose gear were about 18 feet in length at which point they separated from the airplane. The left main landing gear and nose landing gear were broken off 90 degrees and to the right of the landing direction. A portion of the left main landing gear strut remained attached to the airplane and a ground scar relating this portion was approximately 45 feet in length. There were no visual indications consistent with the right main landing gear touchdown.

The airplane was inspected during a "Hi time Inspection" on August 28, 2006, at a total aircraft time of 5,639.3 hours. During this inspection, the mechanic had removed and sent the main landing gear struts for nondestructive testing, but the struts were lost during shipping. The mechanic then ordered a second set of landing gear struts as a replacement for the lost struts. He installed the second set of landing gear struts on the airplane but later determined that the they were not the correct struts. The airplane owner then ordered a third set of struts from North Sound Aviation, Sedro Woolley, Washington, and were installed onto the airplane.

The Federal Aviation (FAA) Form 337, Major Repair And Alteration, that accompanied the landing gear struts was signed by a U.S certificated mechanic who is the owner of North Sound Aviation, which is not a certificated repair station. The Form 337 was dated March 6, 2006. The left and right main landing gear struts are identified on the Form 337 as serial numbers 3P13 and 3P82, respectively. Item 8. Description of Work Accomplished, on Form 337 states:

Main Landing Gear Repairs:

1. Stripped all previously applied paint products from L.H. gear leg S/N 3P13, and from R.H. gear leg S/N 3P82.

2. Checked both above listed main landing gear legs for correct contour configuration and strength. Both gear legs are of the correct contour and strength.

3. Both above listed mani [sic] landing gear legs magnafluxed by North Sound Aviation on their Report of Magnetic Particle Examination dated March 30, 2006. No defects noted.

4. Both above listed gear legs finish cleaned, and primed with Ditzler DP-50LF epoxy chromate primer.

The approved data to accomplish the above listed repair was not cited on Form 337.

An FAA Blue Ribbon airplane record report shows that Form 337 relating to the landing gear strut repair is not present in FAA aircraft records. Advisory Circular 43.9-1E (superceded on January 25, 2007), Instructions for Completion of FAA Form 337 states that the person who performs or supervises a major repair or major alteration should prepare Form 337 and executed at least in duplicate. The person installing a repaired part will forward a duplicate copy to the local FAA district office within 48 hours after the work is completed. The AC also states that the approved data used as the basis for approving the major repair or alteration for return to service should be identified and described on the Form 337 Item 8. Description of Work Accomplished.

The landing gear strut was examined by the National Transportation Safety Board Materials Laboratory. The strut was transversely fractured about 15 inches from the lower end. Visual examination showed that most of the fracture contained overstress features that emanated from near the forward edge of the strut. The mating face of the fracture (on the inboard or upper portion of the strut) was severely damaged during the accident. The strut portion showed that most of the exterior surface contained an intact layer of white paint. In many locations throughout the strut, the paint appeared to have been applied to an irregular or pitted surface.

No portion of the fracture contained dark or rust-colored oxidation products, indicating that no portion of the fracture had been exposed to the environment for an extended period of time. There were four fracture zones of interest associated with a fracture origin area located adjacent to the forward edge of the leg. The overstress propagation was in a direction away from the origin area. Fracture zone 1 contained a mixture of intergranular feature and overstress feature, with the intergranular feature more predominant closer to the forward edge of the strut. Fracture traces or radial marks associated with overstress fracture features within zone 1 indicated that fracture propagation was generally aft from the forward surface. Zone 1 was on a higher plane compared to adjacent portions of the fracture.

Zone 2 contained a mixture of overstress and intergranular features and also contained a relatively thin band of fatigue cracking around most of its perimeter. The overstress regions within zone 2 emanated from a portion of the boundary of zone 1. The portion of zone 2 closer to the inboard/lower surface of the strut was separated from zone 1 by a vertical shear fracture ledge. Fatigue cracking initiated at the perimeter of the overstress region within zone 2 with a greater amount of fatigue propagation on the portion of the perimeter of zone 2 closer to the inboard/lower surface of the strut and with little or no fatigue cracking on the portion of the perimeter of zone 2 further from the inboard/lower surface of the strut.

Zone 3 contained only overstress features with propagation away from the fatigue cracking region at the perimeter of zone 2. Zone 3 could be considered to be the final overstress region (zone 4). Zone 3 appeared to undercut a portion of zone 1, suggesting that this undercut portion of zone 1 might have remained with the mating face of the fracture.

Zone 4 contained only overstress features with propagation away from the perimeter of zone 4. No crack arrest positions were noted within zone 2, consistent with a final overstress region under a single load application.

A metallographic section through the approximate center of zone 1 of the fracture was prepared for examination. A section within zone 1 showed altered microstructural layer adjacent to the surface, indicative of excessive thermal input such as welding. The altered microstru