CREEDE, CO, USA
N221NC
Beech B90
The flight instructor said the airplane felt like it was being pushed down onto the runway. As power was added, the airplane touched down 'approximately 90 KIAS (a loss of 10 to 15 knots indicating a shear)' and there was a loud 'bang.' The airplane became airborne momentarily, then touched down again. The airplane departed the right side of the runway on its nose and left main landing gear. The owner-pilot receiving instruction said 'the bottom fell out and a moderately hard landing was made on the main gear. A pilot who witnessed the accident landed hard moments before. He said he had encountered a 'vertical wind shear.' He saw a large puff of blue gray smoke come out from beneath the right wing, followed by the tumbling right main gear. Metallurgical examination of the right scissors torque link disclosed multiple fractures and a crack in the upper link. The fractures were 'typical of fatigue cracking,' originating from 'multiple sites.' There was also corrosion pitting. Two other fracture sites were 'indicative of overstress.'
On June 25, 1999, at 1317 mountain daylight time, a Beech B90, N221NC, was substantially damaged when it collided with terrain while landing at Mineral County Memorial Airport, Creede, Colorado. There were no injuries to the commercial pilot in command, the private pilot receiving instruction, five passengers, and a dog. Visual meteorological conditions prevailed, and an IFR flight plan had been filed. The flight originated in Oklahoma City, Oklahoma, at 1120 central daylight time. Both pilots submitted written statements. The pilot in command said that as they crossed the runway threshold, it felt like the airplane was being pushed down to the runway. As power was being added, the airplane touched down "at approximately 90 KIAS (a loss of 10 to 15 knots indicating a shear)" and there was a loud "bang." The airplane became airborne momentarily, then touched down again. The airplane departed the right side of the runway on its nose and left main landing gear. According to the second pilot (who owned the airplane and was receiving instruction from the flight instructor), he was the pilot flying (PF) and it was decided that an extra 10 knots would be maintained during the landing approach due to the airport elevation and wind. Two pilots who had already landed advised them that the wind "was approximately 5 knots and mostly down the runway." The landing approach was made with the landing gear extended, flaps set at 60 percent, and airspeed between 110 and 120 knots. Two miles from the runway, "moderate to severe turbulence" was encountered, and airspeed dropped to 110 knots. Power and speed adjustments were made and it was noted that the windsock was extended 50 percent and indicating a left quartering wind. As the airplane was flared for landing, "the bottom fell out and a moderately hard landing was made on the main gear. A loud bang was heard, and the flight instructor assumed control of the airplane. A pilot witnessed the accident and submitted a written statement. He had landed in a Cessna 182 approximately 20 minutes before the accident. There had been "strong turbulence" during the approach, and the landing was in a 90 degree left crosswind with 10 to 15 knot gusts. Over the runway, he encountered a "vertical wind sheer" [sic] and the airplane landed hard. Shortly thereafter, he watched as a Mooney and a Cessna 210 landed "long," but a passenger quipped that it was "typical for a Creede summer afternoon." The pilot then watched the approach and landing of the King Air. He said the approach looked "a little hot. But not excessive." The left crosswind was suddenly gusting 15 to 20 knots. The airplane made a "strong flair" [sic] and a "hard landing," but not "excessive." He said the "wing tips shook a little, then a large puff of blue gray smoke came out from under the right wing, followed by the right main gear, which was tumbling behind, bouncing to about 20 feet into the air. The right scissors torque link (hereafter referred to as "scissors") was sent to NTSB's Materials Laboratory for examination [because of the similarity of failure, FAA's Flight Standards District Office (FSDO) in Denver submitted the left scissors torque link from another Beech airplane involved in a landing gear failure]. According to the laboratory's report (99-242), there were multiple fractures and a crack in the upper link. Fracture surface R1 was "typical of fatigue cracking." It originated from the surface of the larger lightning hole in the center of the link and progressed to a smaller lightning hole at the top of the link. "The origin portion of the fatigue region contained a series of ratchet marks, typical of initiation from multiple sites." There was also corrosion pitting. Fracture R2 was also typical of fatigue, emanating "from the larger lightning hole, and ratchet marks were found on a portion of the fatigue region." After opening the crack, dubbed R6, evidence of fatigue was noted and contained "ratchet marks indicative of initiation from multiple places on the inside of the web. No indication of corrosion pitting was noted on the exterior surface of the link in the area of the initiation of the fatigue cracking." Fractures R3 and R4 had a matte appearance and showed numerous 45 degree angles, indicative of overstress. Hardness and conductivity tests were 83.5 HRB and about 35% IACS, respectively. Typical values (for 2014-T6 aluminum alloy) is 84 HRB and 40% IACS, respectively.
Overload failure of the right main landing gear scissors torque link precipitated by preexisting fatigue fractures. A factor was wind shear.
Source: NTSB Aviation Accident Database
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