Incident Overview
At approximately 1648 Alaska daylight time on July 11, 2015, a Cessna 210 airplane (registration N3607Y) equipped with retractable landing gear sustained substantial damage during landing at Juneau Airport (JNU), Juneau, Alaska. The pilot and a single passenger were uninjured. The aircraft was operated under Title 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed at the time, and no flight plan was filed.
Landing Gear Malfunction
According to an interview with the NTSB investigator-in-charge, the pilot reported that while approaching Hoonah Airport, he set the flaps to 20 degrees and selected the landing gear handle down. The nose gear extended and locked, but the left and right main landing gear extended only halfway and stopped. The pilot then cycled the landing gear selector to the up position, but the gear did not move despite hearing the hydraulic pump run. Returning the selector to the down position, the pilot decided to divert to Juneau Airport, which had Aircraft Rescue and Fire Fighting (ARFF) personnel and equipment. He estimated that during the flight from Hoonah to Juneau, he pumped the emergency hand pump hundreds of times without ever feeling resistance in the hydraulic lines.
Post-Landing Examination
After the landing, the airplane was lifted with a crane to manually pull the landing gear into position and secure it with pins. While the aircraft was in a level attitude, hydraulic fluid was observed leaking from the bottom. On August 5, 2015, an FAA air safety inspector and a certified mechanic, under NTSB direction, examined the hydraulic system. The reservoir was filled, and the emergency hand pump was operated, revealing a large leak under the pilot seat. Removal of the floor inspection panel showed a fracture in the left main landing gear hydraulic actuator at the end cap and along its side.
Actuator Fracture Analysis
The hydraulic actuator (part number 1280501-1, serial number 21058107) was sent to the NTSB Materials Laboratory for detailed examination. It exhibited cracks about the barrel section adjacent to the end cap, consisting of both circumferential and longitudinal components. After removing the end cap, a crescent-shaped fragment of the barrel separated. Scanning electron microscope examination revealed two thumbnail-shaped cracks with striations consistent with fatigue crack propagation. The remaining fracture surface showed dimple rupture, indicative of overstress. Ratchet marks at the thumbnail-shaped cracks suggested multiple fatigue crack initiation sites. No material or mechanical defects were found at these initiation sites, but multiple corrosion pits were observed on the surface of the retaining ring groove.
Weather Conditions
The nearest weather reporting station was Juneau Airport. At 1553, the METAR reported wind from 120 degrees at 11 knots, few clouds at 500 feet, broken at 2,700 feet, overcast at 5,500 feet, visibility 10 statute miles, light rain, temperature 60°F, dewpoint 55°F, and barometric pressure 29.72 inHg.
The pilot did not complete and return the required NTSB Accident Reporting Form 6120.1.