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On May 2, 1996, at 1624 mountain daylight time, a Beech 1900D, N154ZV, operated by Mesa Airlines as United Express flight number 7591 from Gunnison, Colorado, to Denver, Colorado, sustained substantial damage when the right main landing gear collapsed during landing roll at Denver International Airport. There were no injuries to the two crew members and nine passengers. Visual meteorological conditions prevailed for this Title 14 CFR Part 135 scheduled passenger flight which departed Gunnison at 1540. An IFR flight plan was filed.
The first officer was flying the aircraft and, according to the captain, when the landing gear was retracted after takeoff from runway 24 at Gunnison, they heard a "bang" and the right main landing gear failed to retract, and the red light in the landing gear selector remained on. After climbing through 10,000 feet msl (above mean sea level), the gear configuration of nose and left main landing gear retracted and right main landing gear extended was confirmed by visual inspection. The crew elected to continue to Denver due to winds at Gunnison and better emergency response capability at Denver. They noted that there was no emergency or abnormal checklist for this type of failure and no performance data for one gear down operation. However, the captain said they thought that, due to light weight and clear weather conditions both en route and at Denver, the aircraft performance was adequate to make the flight.
When the flight arrived in range for arrival at Denver International Airport, the crew positioned the landing gear selector to the down position to check the landing gear prior to notifying air traffic control of their problem. After selecting the gear down, they had a normal indication that all landing gear were down and locked, and after selecting full flaps they did not have a landing gear warning horn, so they continued the approach to a normal landing on runway 7. Landing reference speed was 111 knots and according to the captain, touch down was smooth and brakes were not used during the landing roll. About 60 knots, the green down and locked light for the right main landing gear began to flicker and the gear warning horn activated intermittently. The captain said he told the first officer to add power and go around and during "spool up" the right main landing gear folded into the wheel well.
The airplane remained on the runway and came to rest on the right side. The captain said he informed the tower and he and the first officer evacuated the passengers through the main entrance door. There were no injuries to passengers or crew and no difficulties with the evacuation.
The Captain qualified as second in command on the Beech 1900 on February 1, 1993, and as captain on November 6, 1994. He holds an airline transport pilot certificate with a type rating in the Beech 1900 and a first class medical certificate dated April 25, 1996. He is required to wear glasses while exercising the privileges of his pilot certificate.
For details of his flight experience, see page 3 of this document.
The first officer qualified as second in command on the Beech 1900 on August 29, 1995. He holds a commercial certificate, single and multiengine land, and an airplane instrument rating. He has a second class medical certificate dated June 30, 1995, and is required to wear glasses while exercising the privileges of his pilot certificate.
For details of his flight experience see Supplement E of this report.
A maintenance records group was formed for this investigation. For details regarding aircraft history and maintenance procedures, see the attached Maintenance Records Group Report.
The nose and main landing gear assemblies are extended and retracted by a hydraulic power pack. In retraction, the nose gear folds aft and the mains fold forward. Micro switches for position indication are located at the knee joint in the drag brace assembly and in the actuator for the main landing gear. Flight deck controls and indicators for normal operation consist of a selector lever, 3 green indicator lights, a red light in the actuator lever, and a warning horn. The green lights for the main landing gear will illuminate whenever the micro switches in the actuator and on the drag brace assembly are closed and indicate the respective landing gear is locked in the down position. The red light will illuminate anytime the selector lever and any of the three landing gear are not in agreement, and the warning horn will sound if landing flaps are selected and all the landing gear are not in the down and locked position.
WRECKAGE AND IMPACT INFORMATION
According to the captain, the right main landing gear collapsed about 60 knots indicated airspeed and folded into the wheel well. The aircraft came to rest on the outer portion of the right wing, left main landing gear and nose gear. During the landing roll/slide, the outer three feet of the right wing, outer trailing edge of the right flap, right main landing gear doors, ventral fin, and the right engine propeller came in contact with the runway surface. The wing, flap, gear doors, and ventral fin exhibited abrasion damage and the composite propeller blades were fractured and frayed at the tips. In addition, the right flap exhibited buckle damage and there were dents in the right side of the fuselage.
The right main landing gear extension/retraction rod was fractured at the spherical bearing, the spherical bearing was binding in the housing, and the rod end attached to the cylinder was bent in the area of the lock nut.
TESTS AND RESEARCH
The right main landing gear retract assembly, upper drag link assembly, and lower drag link assembly were sent to the Safety Board's Materials Laboratory for further examination. The laboratory's report is attached and the examination provided evidence that the spherical bearing in the actuator rod end was dry and showed no evidence of lubrication and the bearing exhibited evidence of wear and binding in certain positions. The examination also revealed that the extension rod failed in fatigue at the outboard end of the retention nut.
The flight data recorder and voice recorder were examined at the Safety Board's laboratories. The examination provided no information contributing to the landing gear failure. Copies of their reports are attached.
The aircraft was released to the Manager of Maintenance, Mountain West Airlines, on May 3, 1996. Parts retained for further examination were the cockpit voice recorder, flight data recorder, landing gear drag link, and right main landing gear extend/retract cylinder. All retained components were returned to the operator following examination.