NTSB Factual Report

On October 10, 2015, about 1100 mountain standard time, a Cessna 310J airplane, N3123L, was substantially damaged during a landing attempt at Tucson International Airport (TUS), Tucson, Arizona. The airplane was operated as a personal flight under the provisions of Title 14 Code of Federal Regulations Part 91. The commercial pilot and his passenger were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight that departed TUS at 1030.

According to the pilot, after a 30 minute flight with a friend they returned to TUS, but received an improper landing gear indication when the pilot attempted to deploy the landing gear. He flew south of the airport to troubleshoot the indication and then returned to the airport. The pilot elected to make a landing attempt after an air traffic controller confirmed the landing gear was extended. During touchdown, the right main landing gear collapsed, and the airplane departed the right side of the runway. A review of accident photographs by a National Transportation Safety Board (NTSB) investigator revealed substantial damage to the right elevator and right aileron.

A flight instructor who was functioning as a passenger observed no abnormalities with the airplane until the landing gear down light failed to illuminate after the pilot attempted to deploy the landing gear. The passenger stated that the pilot used emergency checklists to troubleshoot the landing gear anomaly, but after several attempts to cycle the landing gear, the green light would not illuminate. They returned to the airport to attempt a landing. The touchdown was "normal and unremarkable", but approximately 3 seconds later the right main landing gear slowly collapsed, and the right wing contacted the ground.

According to Federal Aviation Administration (FAA) records, the airplane was manufactured in 1965, and registered to Leading Edge Aviation on April 13, 1992. The airplane's most recent airworthiness certificate was issued on November 22, 1985.

The airplane was powered by two Continental Motors, Inc. IO-520-E, normally-aspirated, direct drive, air cooled, 300 hp engines. A review of the airplane's maintenance records revealed the most recent annual inspection was completed on June 23, 2015, at 4,068 hours of total time in service. The airplane's most recent logbook entry indicated that a landing gear swing and extension were completed during the airplane's last annual inspection.

The 1053 mountain standard time recorded weather observation at TUS, located at the accident site, included winds from 110 degrees at 14 knots, visibility 10 statute miles, clear, temperature 29 degrees C, dew point 12 degrees C, and an altimeter setting of 30.17 inches of mercury.

The airplane is equipped with a fully retractable tricycle landing gear system comprised of two main landing gear wheels beneath each wing and a nose landing gear in the forward fuselage. Each landing gear is mechanically connected to a gear box located aft of the pilot's seat, driven by a motor, and actuated by a landing gear switch on the instrument panel.

An examination of the landing gear system was performed by a representative of the airframe manufacturer and an airframe and powerplant mechanic with oversight from the NTSB and the FAA. Initial inspection of the mechanical linkage within the landing gear wells showed no obvious signs of separation or failure; however, both main gear side brace lock links were disengaged by hand with little force when pulled together.

The main landing gear intermediate drive tubes were disconnected, and a free fall test was performed to verify each gear could extend to the down and locked position. The main landing gear were retracted by hand about 30 degrees and dropped separately. Each gear returned to its down and locked position, and the locks were then disengaged by hand with little application of force.

The floor panels and seats were removed to facilitate an examination of the motor assembly and drive tubes, which revealed the non-adjustable tube separated outboard a few inches from a lever attached to a clevis fitting. The drive tube signatures indicated that it failed in compression on the forward/aft plane. A contact signature was observed on the base of a clevis that connected the tube to a lever. According to the airframe logbook, the non-adjustable drive tube (p/n 0841138-1) was recently installed during an annual inspection that took place on June 23, 2015. The entry described the part as a "main gear retraction tube," and included the corresponding part number.

Both landing gear actuator limit switches on the gear motor were tested to verify the landing gear "up" and "down" indications operated normally. The limit switches were tested separately with the battery on, and no anomalies were observed when the landing gear "up" indication was tested, but the landing gear "down" indication failed to illuminate. An electrical continuity test of the landing gear down actuator limit switch revealed the switch functioned intermittently. The down indicator switches on the main landing gear and wiring were not tested. According to the airplane's logbook, the landing gear actuator down limit switch was replaced on September 26, 2015.

A hanging scale was used to measure the down lock tension for the main landing gear. The hook end of the hanging scale was attached to the lock link and pulled at a right angle. The left main landing gear down lock tension was about 17 lbs and the right main landing gear tension was about 11 lbs. According to the manufacturer, the prescribed tension is 40 to 60 lbs. for proper engagement and tension. The fork bolt is normally used to adjust down lock tension; however, the bolt was covered in grime indicating that it had not been adjusted during recent inspections.

According to the pilot, he encountered a right main landing gear failure during a previous flight in 2013. He suspected the landing gear failure was caused by a passenger seated in the rear right seat who damaged the floor panels with his foot during a flight before the first landing gear incident. Several mechanics visually inspected the airplane following the first incident, and discovered damage to the floor panels and landing gear drive tubes located under the front right seat in the cockpit. The tubes and right main landing gear switch were subsequently replaced by a mechanic who was assisted by the pilot.

The mechanic responsible for endorsing the airplane's last annual inspection reported that he started working on the accident airplane in 2014. He was asked to inspect the airplane following the installation of several components that were replaced as a result of the pilot's previous landing gear anomalies. According to the mechanic, he placed the airplane on jacks and performed multiple landing gear swings, but did not observe any abnormalities.

The pilot stated that the manufacturer's service manual was used to inspect the airplane; however, the airplane rigging procedure, which included a procedural item to verify the landing gear down lock brace tension, was not used during any of the inspections that followed the first landing gear failure.

NTSB Probable Cause

The insufficient right main landing gear (MLG) down-lock tension due to maintenance personnel's failure to perform a rigging procedure during the airplane's most recent inspection, which resulted in the right MLG collapsing during landing.