NTSB Identification: LAX97LA019.
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Nonscheduled 14 CFR
Accident occurred Tuesday, October 15, 1996 in PHOENIX, AZ
Probable Cause Approval Date: 12/18/1998
Aircraft: Aero Commander 690, registration: N15VZ
Injuries: 4 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 pilot reported that during flight, the nose gear dropped from the wheel well, he noted the hydraulic pressure had dropped to 600 psi, & the landing gear in-transit light illuminated. He said he accomplished emergency procedures, but was unable get the main landing gear to lock in the down position. The main landing gear collapsed during touchdown, & the belly of the airplane was damaged. The brake & landing gear systems were powered by 2 engine driven pumps (1 on each engine) & an auxillary (electrical) pump. For backup operation, gas pressure from an emergency nitrogen storage cylinder was continuously provided to a 2nd set of main gear actuators to provide pressure for main gear extension. During gear retraction, nitrogen was compressed back into the nitrogen cylinder. During extension, hydraulic pressure & nitrogen pressure work together to extend the main gear. After the accident, a hydraulic fluid leak was found at a hydraulic line fitting on the right main landing gear brake system, but no other leak was found. The leak was repaired, & the landing gear was functionally checked; the retraction & extension cycle functioned normally, & no system fault was found. No reason was found to explain why gas pressure from the emergency nitrogen storage cylinder did not lock the main gear in the down position.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: failure of the main landing gear to fully engage in the down-and-locked position for undetermined reason(s). Loss of hydraulic pressure to the main gear for undetermined reasons(s) was a related factor. Full narrative available
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