Accident Sequence
On January 27, 2009, at about 1110 Pacific standard time, a Cessna 210, registration N210TF, collided with terrain after sliding off the runway during a landing with its main landing gear partially extended at Henderson Executive Airport, Las Vegas, Nevada. The sole occupant, an airline transport pilot, was not injured. The airplane, belonging to a client of the pilot's company, sustained substantial damage.
The flight was a 14 Code of Federal Regulations Part 91 post-maintenance test flight that had departed Henderson Executive Airport about 45 minutes prior. The flight operated in visual meteorological conditions, and no flight plan was filed.
According to the pilot, the test flight aimed to confirm proper function of the landing gear retraction and extension system and the flap activation system following maintenance on the hydraulic system. Shortly after takeoff and turning out of the traffic pattern, the pilot retracted the landing gear. After that sequence completed, he lowered the landing gear handle to the down position, but the main landing gear only extended partway. He attempted to recycle the gear to the up position; the nose gear remained down, and both main gear remained partially extended. Unable to lower or retract the gear using the normal system, the pilot tried the emergency extension hand pump, which also failed. His attempt to extend the flaps was unsuccessful. After airport emergency equipment was in position, the pilot landed with the nose gear fully extended and both main gear partially extended. Following touchdown, the airplane initially stayed on the runway but eventually slid off the side and collided with uneven terrain, causing internal damage to the horizontal stabilizer.
Maintenance History
The airplane's owner originally brought it to the maintenance facility due to a hydraulic leak. During troubleshooting, the hydraulic power pack would not operate the flaps with the engine running, and the emergency extension gear handle had excessive pressure against it after engine shutdown. The hydraulic leak was traced to the overflow vent line from the power pack.
The hydraulic power pack, which controls landing gear extension/retraction and flap positioning, was removed and replaced with a used serviceable unit. The replacement unit and the system were leak-checked and operationally tested with a hydraulic service mule, including a normal landing gear swing and an emergency gear extension check. During testing, a couple of leaks at the hydraulic pack fittings were repaired with new seals.
After removal from jacks, an engine ground run tested the engine-driven hydraulic pump and flap operation. The airplane was then left for a couple of days to confirm no ongoing leaks. A subsequent flight for a post-maintenance operational check revealed that the landing gear retracted normally but did not fully extend when the gear handle was lowered; the pilot extended the gear using the emergency hand pump and landed uneventfully. Following that flight, the hydraulic pump was replaced with an overhauled unit, and the gear and flap systems were again tested with the service mule and an engine ground run. The accident flight followed.
Post-Accident Investigation
A post-accident inspection of the airplane's hydraulic system and fittings revealed no evidence of anomalies or fluid leakage. The hydraulic power pack and engine-driven pump were removed and sent to the Federal Aviation Administration Aircraft Certification Office in Wichita, Kansas, for oversight of testing and inspection at FAA-approved repair stations.
Component Examination
The hydraulic pump (Cessna Part Number 20240-LCB, Serial Number 112) was tested at Ametek B & S Aircraft Parts and Accessories. It met required specifications at ambient temperature (about 100°F) and at an operational fluid temperature of about 145°F. The pump was not disassembled.
The hydraulic pack (Electrol EA1332-1, Serial Number X-001) was manufactured in 1974 and overhauled by Airight Products at an undetermined date. At APPH Wichita, Inc., it underwent a functional test and disassembly inspection. Although the pack functioned properly on the test bench, including successful emergency extension hand pump activation, several discrepancies were noted: leakage past some poppet valves, permanent set deformation of larger O-rings (flat on one side), visible witness marks on poppet valve seats, wear of the poppet valves (not excessive for the unit's age), and a fine black residue on some internal components. According to APPH personnel, the residue likely resulted from an overheat condition at some point in the past, and the pack appeared to be an old unit in need of an overhaul.
The APPH technician who tested and disassembled the unit suggested that the pack may have malfunctioned in both normal and emergency gear extension modes due to a restriction of poppet valve movement or alignment from internal contamination. Such contamination could have been dislodged by forces during the accident and flushed from the system by fluid flow during the bench test. No other anomalies or issues with the gear and flap actuating systems were found.