PHOENIX, AZ, USA
N15VZ
Aero Commander 690
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.
On October 15, 1996, at 0300 hours mountain standard time, an Aero Commander 690, N15VZ, collided with the runway surface after the landing gear collapsed on runway 26R at the Sky Harbor International Airport, Phoenix, Arizona. The airplane sustained substantial damage. The airline transport pilot, two flight nurses, and one patient were not injured. The airplane was being operated by Sun West Aviation, Inc., Ogden, Utah, as an air medical transport flight under 14 CFR Part 135 when the accident occurred. The flight originated from Show Low, Arizona, at 0158. Visual meteorological conditions prevailed at the time and a company VFR flight plan was filed. The pilot reported a hydraulic failure 35 miles east of Phoenix. He indicated the landing gear in transit light stayed illuminated and he was unable to get the landing gear to lock using the emergency extension procedure. The landing gear collapsed during touchdown and the airplane slid to a stop. The damage to the plane was limited to the belly area of the fuselage. The airplane was examined by the Federal Aviation Administration (FAA) and was found to have an hydraulic fluid leak at a hose attachment fitting to the right main landing gear brake system. Examination of the fitting revealed the hydraulic line had fractured at the flare joint in the fitting. On November 21, 1996, the landing system was functionally checked after the leak had been repaired. The check included testing of the emergency extension procedure. According to the FAA there were no defects noted with the airplane's landing gear system.
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.
Source: NTSB Aviation Accident Database
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