NTSB Factual Report

HISTORY OF FLIGHT

On June 4, 2001, at 1932 Pacific daylight time, Vision Air Flight 12, a Piper PA-31-350 twin engine airplane, N209TA, departed the right side of the runway after the right main landing gear collapsed during the landing roll at North Las Vegas, Nevada. Aviation Ventures, Inc., of North Las Vegas was operating the airplane as an on-demand passenger sightseeing flight under the provisions of 14 CFR Part 135. The commercial pilot and 9 passengers were not injured. The airplane sustained substantial damage. The cross-country flight departed Grand Canyon, Arizona, approximately 1830, and had a final destination of North Las Vegas. Visual meteorological conditions prevailed, and a company flight plan had been filed.

According to the pilot's written statement, after departure from Grand Canyon he noted that the landing gear unsafe light was illuminated. He cycled the landing gear as part of an effort to resolve the discrepancy and obtained three green down and locked lights. He cycled the gear up, and the nose and left main landing gear retracted. However, the right main landing gear was still showing a down and locked condition. The pilot cycled the gear down once more and received a down and locked indication for all three landing gear. At this point, he elected to leave the landing gear extended and completed the balance of the flight to North Las Vegas.

He reported that the landing touchdown was "relatively gentle" and the nose wheel settled to the runway. When he applied the brakes, the airplane yawed "severely" to the right as the right wing settled toward the ground. The pilot pulled the mixture controls to idle cutoff, and also placed the fuel shutoff valves to the off position. As the right wing tip dragged on the ground, the airplane departed the runway to the right and crushed the right wing. The pilot completed an emergency shutdown checklist, and all occupants deplaned in a normal manner through the cabin entry door.

One of the passengers later reported to the National Transportation Safety Board that she had sustained "a severe cervical spine injury" as a result of the accident. She added that the touchdown was not gentle.

AIRCRAFT INFORMATION

The airplane is equipped with a hydraulically actuated, retractable tricycle landing gear. The cockpit controls incorporate a wheel-shaped handle that is pulled out and placed in the up (landing gear retracted) position or the down (landing gear extended) position. There are four landing gear indication lights, three green lights (one for each landing gear), and one red light. When the three green lights are illuminated, the system indicates that the landing gear are down and locked. The red light will illuminate when any landing gear is not down or not up and locked. There is no indication for a landing gear up and locked position.

According to the operator, the accident airplane was on a Federal Aviation Administration (FAA) Approved Aircraft Inspection Program, and the last inspection occurred on May 19, 2001, 47.9 hours prior to the accident. According to the operator's Director of Maintenance, the airplane would have undergone a complete inspection cycle at least every 200 hours.

WRECKAGE AND IMPACT INFORMATION

The FAA inspector, who responded to the accident site, examined the airplane. He observed a fractured component in the landing gear up-lock assembly. The Piper PA-31-350 parts manual described the fractured part as a main gear retraction arm, part number 42042-00. The arm attaches the right main landing gear's forward side link assembly, the main landing gear lock rod (or cable) assembly, and the hydraulic actuator. The retraction arm is constructed with an elongated bolt hole in the center and a bend angle between the two ends (resembling a miniature boomerang). One end contains a fork for the acceptance of the actuator rod-end, and each end contains its own bolt hole(s). The retraction arm was shipped to the Safety Board Materials Laboratory in Washington, DC, for further examination.

TESTS AND RESEARCH

The Materials Laboratory examined the retraction arm fracture surfaces both visually and microscopically after it had been cleansed in acetone. The arm fractured through the elongated bolt hole creating approximately two equal halves and two fracture surfaces; one below the elongated hole and one above the hole.

The bottom fracture surface was on a flat plane and contained crack arrest marks, which are "visible crack positions created as the crack propagates through the material." There were also multiple ratchet marks, which are "[steps] on the fracture face that separate two fatigue cracks that initiate at different origins and propagate on slightly offset planes," near the origin area. The cracking originated from the exterior surface of the arm in the bend angle, progressed upward, in the direction of the center bolt hole, and extended through about 75 percent of the fracture surface. Microscopic examination of the exterior surface showed no obvious defects.

The top fracture surface displayed a rough matte surface and necking (elongation, like stretched taffy) deformation, which are features typical of an overstress fracture.

After examining the fracture surfaces, laboratory technicians reassembled the arm as close as possible to its original shape. The technician measured the radius in the bend angle with an OGP, Inc., SmartScope, and the average radius measurement was approximately 0.20 inch. According to the manufacturer's specifications, the radius in the bend angle should be 0.50 inch. The technician also noted out-of-plane bending deformation in the vicinity of the top fracture; the fork end appeared to be bent aft compared to what should have been its normally installed position.

ADDITIONAL INFORMATION

According to the operator, the fractured retraction arm had accumulated an estimated 13,231.2 hours since new. A search of the FAA's Service Difficulty Reports (SDR) revealed five records of retraction arms found cracked or broken. One retraction arm was "found cracked during [a] 100-hour inspection," and had accumulated 10,691 hours. Another cracked retraction arm was detected "during a detailed [visual] inspection of the landing gear." According to this SDR, the arm "connects the hydraulic actuator to the forward side brace which extends and retracts the landing gear. The weight of the gear and the speed of moving the gear up and down eventually fatigues [the] part [and] recurrence cannot be avoided." That particular arm had accumulated 15,290 hours prior to cracking. Another arm found broken in Australia had accumulated 21,330 hours prior to failing.

Review of the PA-31-350 Service Manual, under section 7-23 titled "Cleaning, Inspection, and Repair of Main Landing Gear," revealed instructions to "inspect the gear housing, side brace links, idler links, rods and attachment plates for cracks bends or misalignment." A warning in section 7-23 refers mechanics to a Piper Service Bulletin (SB 845A), which defines specific inspection/replacement instructions for the main landing gear forward side brace. Service Bulletin 845A offered an option to PA-31-350 owners to inspect the forward side brace after accumulating 1,000 hours total time and conduct a repetitive inspection every 100 hours, or replace the forward side brace with an "improved" side brace and discontinue the repetitive inspection. During the replacement of this brace, the SB called for the inspection of "main landing gear attach points and brackets for security and integrity."

The replacement of the forward side brace with the improved brace was mandated after 1,200 hours of time in service in a 1996 Airworthiness Directive (AD 96-10-14). According to the operator's Director of Maintenance, the accident aircraft had complied with the AD a few years before the failure of the retraction arm.

All of the retraction arm cracks or failures found during the SDR search failed years after the AD effective date (June 27, 1996).

A Safety Board investigator examined an exemplar PA-31-350 landing gear assembly. The retraction arm was accessible, and the Safety Board investigator noted the accident airplane's retraction arm crack origin area was visible. According to the exemplar aircraft's mechanic, the retraction arm is easily inspected and removal and replacement would not require additional landing gear rigging.

NTSB Probable Cause

fatigue failure of the right main landing gear retraction arm.