On August 9, 1997, at 1230 hours mountain standard time, a Cessna 310, N8139M, sustained a right main landing gear collapse during the landing touchdown on runway 22 at the Mesa, Arizona, airport. The aircraft sustained substantial damage. The airline transport rated pilot and the commercial pilot were not injured. The aircraft was being operated as a training flight under 14 CFR Part 91 by Aex Air Inc., of Tempe, Arizona, when the accident occurred. The flight originated at Phoenix Sky Harbor Airport at 0835. Visual meteorological conditions prevailed.

According to written statements from both pilots, the training flight lasted about 3 hours, included several landings, and was returning to Phoenix. On the final approach to land at Phoenix, the pilot put the gear selector down and obtained a green light indication. During main gear touchdown the gear warning horn sounded and the pilot performed a successful go-around. The pilots elected to leave the landing gear down during the climb out and then proceeded to a safe location to assess the problem. During this portion of the flight, the green down light went out. Subsequent attempts, to include both the normal and emergency procedures in the POH, to obtain a green down light on the landing gear were unsuccessful. The pilots landed at Mesa and the right main landing gear collapsed.

Postaccident examination of the aircraft revealed that the right main gear upper side link had fractured, separating it from the lower side link. The associated push-pull tube for the upper side link was bent and the attaching bolt sheared. The upper and lower side links form the down lock for the main landing gear.

The right main landing gear components were sent to the Federal Aviation Administration (FAA) Wichita Aircraft Certification Office. A certification engineer from that office then took the components to Cessna Aircraft metallurgical laboratories for examination under supervision. According to a report of the examination, the components met the chemical, hardness, and process specifications listed in the production drawings. The report noted that all fractures and bends were the result of overloads. A complete report of the findings is appended to this report.

On May 28, 1997, this aircraft sustained damage while it was parked on the ramp at the Burbank, California, airport. The event occurred while a Boeing 727 was departing the ramp. According to witnesses, as the 727 turned, it's jet blast lifted the Cessna off the ground and actually pulled one lineman into the air before the aircraft was abruptly deposited back on the ramp. Damage was noted to the rudder and one flap. Following the incident, the aircraft was ferried to Chino, California, for repair. The Safety Board obtained a copy of the invoice and estimate for repairs to the damaged aircraft. In a letter to the operator dated June 1, 1997, Aircraftsman submitted an estimate which included as item 10, "jack aircraft and inspect nose gear assembly, actuator and bellcrank and nose structure," and item 11, "perform gear retraction and extension check." Despite numerous attempts by the operator, the FAA, and the Safety Board, no work orders or job cards were located at the maintenance facility to document the maintenance items that were performed during the June 1-2 shop visit.

The Safety Board discussed this accident with the Cessna Aircraft Company Product Safety Department. According to the manufacturer, it is possible to perform a gear retraction and extension check, which operates normally, without discovering any damage to the gear. Furthermore, the gear can operate normally for an unknown period of time, then at a later date, fail to operate properly. The manufacturer also stated that following the incident at Burbank the airplane should have undergone an extensive re-rigging of the gear, which would have also included tension check on the down lock of between 40 and 60 pounds. If the tension was not somewhere in this range, the 310 Service Manual calls for re-rigging as necessary to prevent collapse of the gear.

The aircraft parts which had been retained for laboratory testing were returned to the operator of the aircraft on January 28, 1998.

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