Sunday, March 12, 2017

Cessna 210C, N3607Y: Accident occurred July 11, 2015 in Juneau, Alaska

The National Transportation Safety Board did not travel to the scene of this accident. 

Additional Participating Entity:  
Federal Aviation Administration / Flight Standards District Office; Juneau, Alaska 

Aviation Accident Final Report - National Transportation Safety Board: https://app.ntsb.gov/pdf

Docket And Docket Items - National Transportation Safety Board: https://dms.ntsb.gov/pubdms

Aviation Accident Data Summary - National Transportation Safety Board:  https://app.ntsb.gov/pdf

http://registry.faa.gov/aircraftinquiry/NNum_Results.aspx?NNumbertxt=N3607Y

NTSB Identification: ANC15LA048
14 CFR Part 91: General Aviation
Accident occurred Saturday, July 11, 2015 in Juneau, AK
Probable Cause Approval Date: 02/13/2017
Aircraft: CESSNA 210, registration: N3607Y
Injuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The private pilot was conducting a personal cross-country flight. In preparation for landing at the destination airport, the pilot selected the landing gear handle to the “down” position. The nose gear fully extended and locked into place, but the left and right main landing gear extended only about halfway and then stopped. The pilot’s efforts to cycle the landing gear were unsuccessful, and he subsequently conducted an emergency landing to an alternate airport, during which the landing gear collapsed upon touchdown with the runway. 

After the accident, the airplane was lifted with a crane and positioned in a level attitude, and hydraulic fluid was observed leaking from the bottom of the airplane. A postaccident examination of the hydraulic system revealed that the left main landing gear hydraulic actuator was fractured due to a fatigue crack that had initiated at the retaining ring recess in the housing and propagated through most of the barrel housing cross-section. Once the actuator was substantially weakened, the housing cracked further from overstress.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
A loss of hydraulic fluid due to a fractured left main landing gear hydraulic actuator as a result of a fatigue crack, which led to the landing gear collapsing upon touchdown.

On July 11, 2015, about 1648 Alaska daylight time, a retractable landing gear-equipped Cessna 210 airplane, N3607Y, sustained substantial damage during landing at Juneau Airport (JNU), Juneau, Alaska. The pilot and passenger were uninjured. The airplane was registered to, and operated by, the pilot under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91 as a personal flight. Visual meteorological conditions prevailed at the time of the accident. No flight plan was on file.

During an interview with the National Transportation Safety Board (NTSB) investigator-in-charge on July 11, 2015, the pilot stated that while approaching the Hoonah Airport, Hoonah, Alaska, the flaps were set to 20 degrees down and the landing gear handle was selected to the down position. The nose gear fully extended and locked into place, but the left and right main landing gear extended about halfway and stopped. The landing gear selector was then placed back into the up position in an effort to cycle the landing gear. The pump was heard running, but the gear failed to move. The landing gear selector was placed again in the down position and in the interest of safety, the pilot decided to change the destination from the Hoonah Airport to the Juneau Airport where there was Aircraft Rescue and Fire Fighting (ARFF) equipment and personnel. He estimates that during the flight from Hoonah to Juneau, he pumped the landing gear emergency hand pump hundreds of times, but he never felt any resistance in the hydraulic lines.

During removal of the airplane from the runway, it was lifted with a crane so the landing gear could be physically pulled into place and secured with pins to prevent retraction. When the airplane was lifted and positioned in a level attitude, hydraulic fluid was observed leaking from the bottom of the airplane.

On August 5, 2015, an FAA air safety inspector from the Juneau Flight Standards District Office, along with a certified airframe and power plant mechanic, under the direction of the NTSB IIC, examined the airplane's hydraulic system. They hydraulic reservoir was serviced to a full level and the landing gear emergency hand pump was manipulated. A large leak was evident under the pilot seat. When the floor inspection panel was removed, the left main landing gear hydraulic actuator was discovered to be fractured at the end cap and along the side. The actuator was removed and sent to the NTSB Materials Laboratory in Washington, DC, for a more detailed examination by a Materials Research Engineer.

The hydraulic actuator (P/N 1280501-1, S/N 21058107) was cracked about the barrel section adjacent the endcap with a circumferential and a longitudinal component. Once the endcap was removed, a crescent fragment of the actuator barrel with the circumferential crack fell away. The fracture surface exhibited two thumbnail-shaped cracks, which were examined using a scanning electron microscope. The thumbnail region displayed striations consistent with fatigue crack propagation. Portions of the fracture surface outside of the fatigue crack revealed dimple rupture, consistent with overstress. The thumbnail-shaped fatigue cracks exhibited ratchet marks, consistent with multiple fatigue crack initiation. Examination of these initiation sites did not reveal any discernible material or mechanical defects. However, examination of the surface of the retaining ring groove did reveal multiple corrosion pits.

A detailed examination report including microscopic images is available in the public docket for this accident.

The closest weather reporting facility is Juneau Airport, Juneau. At 1553, an aviation routine weather report (METAR) from the Juneau Airport was reporting in part: wind from 120 degrees at 11 knots; sky condition, few at 500 feet above ground level (agl), broken at 2,700 feet agl, overcast at 5,500 feet agl; visibility 10 statute miles; light rain; temperature 60 degrees F; dewpoint 55 degrees F; barometric pressure 29.72 inHg. 

The pilot did not complete and return the required NTSB Accident Reporting Form 6120.1.

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