NTSB Factual Report

On December 11, 2008, about 1311 eastern standard time, a Cessna 402C, N522FA, registered to Friendship Airways Leasing, Inc., operated by Friendship Airways, Inc., dba Yellow Air Taxi, experienced separation of the left main landing gear assembly during the landing roll at the Fort Lauderdale/Hollywood International Airport (FLL), Fort Lauderdale, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed for the instructional flight conducted under 14 Code of Federal Regulations (CFR) Part 91. The flight departed from Palm Beach County Glades Airport (PHK), Pahokee, Florida. The airplane sustained minor damage and the airline transport-certificated check pilot (ATP), commercial-certificated pilot receiving instruction, and two passengers were not injured.

The pilot receiving instruction was training to be the company's chief pilot, and the two passengers were new-hire pilots observing. The check pilot was also a certificated flight instructor, and had provided training to all three pilots throughout the day. The pilot receiving instruction, seated in the left pilot seat, and who was the pilot flying (PF), stated that after takeoff the flight proceeded to the destination airport and was cleared to land on runway 27L. The winds at the time were from the south at 12 knots and upon touchdown, the longitudinal axis of the airplane was aligned with the runway centerline. During the landing roll, he heard an abnormal sound from the left side of the airplane and one passenger shouted that the left wheel assembly had separated. The left propeller blades contacted the runway and the PF secured both engines and the airplane's electrical system. The airplane arched to the left and contacted one runway light before coming to rest on grass off the left side of the runway.

A surface observation weather report taken at Fort Lauderale/Hollywood International Airport, Fort Lauderdale, Florida, at 1253, or approximately 18 minutes before the accident indicates the wind was from 190 degrees at 14 knots with gusts to 20 knots, and the visibility was 10 statute miles. Broken clouds existed at 2,200 feet, and the temperature and dew point were 26 and 22 degrees Celsius respectively. The altimeter setting was 29.86 inches of Mercury.

Examination of the airplane revealed the left upper barrel and trunnion assembly was fractured. The part was retained for further examination by the National Transportation Safety Board's Materials Laboratory.

Examination of the upper barrel and trunnion assembly by the Safety Board's Materials Laboratory revealed the barrel assembly was fractured through the cylindrical barrel portion starting about 0.20 inch below the side brace collar. The fracture followed the transition between the thinner wall section of the barrel below the side brace collar and the thicker wall region within the collar. The fracture was located at a point where the wall thickness transitioned by design to a smaller amount. A flat crescent-shaped fracture region existed around approximately 90 degrees of the barrel perimeter, and was oriented normal to the longitudinal axis of the barrel. The topography and surface features within the crescent were indicative of fatigue progression. The fatigue propagated through an estimated 70 percent of the barrel wall thickness, with the remainder of the fracture on a slant plain through the barrel wall indicative of tensile shear overstress. Ratchet marks indicated the fatigue initiated at multiple origins on the outer diameter surface along the entire crescent region. Crack arrest marks indicate the fatigue crack propagated radially inward with little or no circumferential propagation.

Further examination of the upper barrel and trunnion assembly revealed the barrel material, heat treatment, and hardness were consistent with the specifications for the part, while the surface finish was less than the specified value. An area of the barrel immediately beneath the fracture surface exhibited smooth areas with corrosion pits. Moderate corrosion was also noted at the upper edge of the side brace collar following paint removal by chemical and mechanical means. Measurements taken of the inside and outside diameters of the barrel at points beneath the fracture were performed. The results of the inside diameter measurements revealed the maximum measured reading was 2.5138 inches, or 0.0118 inch greater than the maximum specified, and the results of the outside diameter measurements revealed the minimum measured reading was 2.6967 inches, or 0.0133 inch less than the minimum specified. The transition area where the fracture was located is specified to have a radius of 0.5 inch. The measured radius of the accident barrel was uneven and no single radius measurement could be used to describe the transition. An optical comparator view of an intact area of the transition in two separate areas indicates 0.135 inch radius on the thinner side wall and 0.339 inch near the thick wall region of the barrel.

The airplane was maintained in accordance with a Federal Aviation Administration Approved Aircraft Inspection Program (FAA AAIP), consisting of 4 inspections at 50-hour intervals. Visual inspection of the landing gear upper barrel and trunnion assembly is performed during the No. 4 inspection.

Review of the maintenance records revealed the landing gear was last visually inspected on November 14, 2008. The inspection specified to check the barrel for corrosion, pitting, and cleanliness. No other inspection requirements are stipulated for the fracture area of the upper barrel and trunnion assembly. The airplane total time at that time was 9,957.4 hours. The airplane total time at the time of the accident was approximately 10,015 hours.

The NTSB has investigated two other accidents in which the upper barrel and trunnion assembly fractured. The first case involved a U.S. registered airplane and occurred in the Bahamas; the NTSB case number is MIA04WA066. The second case also involved a U.S. registered airplane and occurred in the U.S.; the NTSB case number is MIA02LA089. Both cases involved fracture above the side brace collar.

NTSB Probable Cause

The airplane manufacturer's inadequate inspection procedure resulting in undetected fatigue cracking of the main landing gear barrel of the upper barrel and trunnion assembly.