NTSB Factual Report

HISTORY OF FLIGHT

On August 11, 2001, at 2052 central daylight time, a Cessna 210 airplane, N8137L, was substantially damaged during landing with the main landing gear retracted at the Fort Smith Regional Airport, Fort Smith, Arkansas. The private pilot and his passenger were not injured. The aircraft was registered to and operated by the pilot. Night visual meteorological conditions prevailed and an instrument flight rules flight plan was filed for the 14 Code of Federal Regulations Part 91 personal flight. The cross-country flight departed Batesville, Arkansas, at 1630, and was destined for Fayetteville, Arkansas.

According to the pilot, he intended on landing at Fayetteville; however, during the landing attempt with a 5 knot variable wind, the "left wing appeared to rise as if encountering a strong crosswind from the left." The pilot aborted the landing and informed the air traffic control tower that he "had a problem." The air traffic controller informed the pilot that his right main landing gear appeared to be trailing behind the airplane. The pilot troubleshot the landing gear system and noticed that the hydraulic reservoir was empty. The pilot's passenger put engine oil in the reservoir, and the pilot again attempted to lower the landing gear to no avail. The pilot elected to land the airplane at Fort Smith, where the airport rescue/fire fighters were "better staffed." The pilot landed the airplane with the nose landing gear extended and the main landing gear retracted.

According to an aircraft mechanic, the airplane's horizontal stabilizer and elevator sustained structural damage. The mechanic examined the landing gear system and found that "the left landing gear actuator was busted." The actuator (part number (P/N) 128100-1, serial number (S/N) 1511) was removed from the accident airplane and sent to the NTSB investigator-in-charge for further examination. There were no other reported anomalies with the hydraulic system, its lines, and its fittings.

AIRCRAFT INFORMATION

The airplane was involved in a gear up landing in September 1999. Following that gear up landing, the landing gear actuators and hydraulic power pack were removed, overhauled, and reinstalled on the airplane in August 2000, at an aircraft total time of 4,205.8 hours.

Review of a work order, provided by the actuator overhaul facility, revealed that the landing gear actuators were "disassembled, cleaned, [and] inspected." The actuators were then sent to another facility for non-destructive inspection of the actuator components. According to paperwork provided by the non-destructive inspection facility, the actuator bodies were inspected via a penetrant inspection method per Military Specification MIL-I-6866. After the actuator components were inspected, they were returned to the overhaul facility, where the piston of actuator S/N 1511 was polished and the actuator was reassembled with new seals in accordance with the Cessna 210 service manual on April 11, 2000.

According to Cessna, the actuator body was forged from 2014 aluminum and then heat treated to the T6 condition. The actuator operating pressure was 1,500 psi with a burst pressure of 3,750 psi. A relief valve in the landing gear system was set to 1,800 psi.

TESTS AND RESEARCH

Examination of the actuator revealed that a crack was present through the length of the cylindrical section of the body. The actuator was deformed with an outward bulging of the body in the area of the crack. The actuator was sent to Cessna Aircraft Company's manufacturing facility with an NTSB investigator for further examination. Cessna conducted a material conformity test by performing a chemical analysis, electrical conductivity test, a hardness test, and a grain flow examination. All of the conformity tests revealed that the actuator met the manufacturer's specifications. The actuator was observed under a stereomicroscope; however, no fracture origin could be found. It was determined that the bulging of the material was due to excess pressure within the cylinder. The source of the excess pressure was not determined.

A search for similar actuator failures was conducted by the NTSB Materials Laboratory in Washington, D.C. Two previous accidents were documented with similar actuator failures (NTSB Accident Numbers FTW97LA370 and MIA92LA188). Three actuators with similar failures were examined by the NTSB Materials Laboratory as a result of the two aforementioned accidents. One of the actuators examined by the NTSB Materials Laboratory was involved in an off airport landing and was exposed to high loads from hitting a ditch. This actuator was examined for comparison reasons. All of the actuators failed in a near identical manner as a result of sudden overstress, and all of the previously examined actuators met and/or exceeded Cessna's manufacturing requirements.

ADDITIONAL INFORMATION

The actuator was returned to the owner on February 4, 2002.

NTSB Probable Cause

the overload fracture of the left main landing gear actuator which resulted in the loss of all hydraulic fluid and led to a wheels up landing.