Final Report: Pilot-heat switch failure led to loss of control

 - March 22, 2007, 9:50 AM

CESSNA 425 CONQUEST I, SAN JOSE, CALIF., MARCH 6, 2002–The NTSB concluded that the in-flight breakup of Conquest N444JV was caused “by the pilot’s loss of control, which resulted in exceeding of the design stress limits of the aircraft, leading to an in-flight structural failure.” The loss of control was blamed on the loss of primary airspeed reference resulting from pitot tube icing, caused by the internal failure of the pitot heat switch. Additional factors were the pilot’s distraction caused by the airspeed reading anomaly and spatial disorientation.

The airplane crashed six minutes after departing Reid-Hillview Airport in San Jose on an IFR flight plan. It was climbing at about 2,000 fpm through 6,700 feet when it began a series of heading and altitude changes inconsistent with its ATC clearance. The airplane turned right and climbed to 8,600 feet, then turned left and descended to 8,000 feet. It turned right and climbed to 8,500 feet, and began a rapidly descending right turn. As the aircraft was descending through 7,000 feet, the pilot advised ATC, “Four Juliet Victor, I just lost my needle give me…” No further transmissions were received and the last radar return showed the airplane descending through 3,200 feet at about 11,000 fpm. The airplane was close to Vmo (230 knots) at the last mode-C return.

An airmet was in effect for occasional moderate rime to mixed icing in clouds and in precipitation and there were multiple cloud layers from 4,000 to 13,000 feet, with a freezing level around 7,000.
Witnesses saw the airplane come out of the clouds in a high-speed spiral descent just before it broke up at about 1,000 feet agl. The aircraft was destroyed and the pilot and two passengers were killed. All structural failures were the result of overload.

The right pitot heat switch was found in the “on” position, while the left switch was in the “off” position. The left pitot heat switch toggle lever was noticeably displaced to the left by impact with an object in the cockpit. With the exception of the left pitot heat, the anti-ice and deice system switches were all configured for flight in icing conditions. The right switch was intact, while the toggle lever mechanism of the left switch was broken loose from the housing. Microscopic examination of the left switch revealed embedded debris and wear marks indicative of an old fracture, which had allowed an internal build-up of large coarse fibrous lint-like debris. The combined effects of the broken housing, the resulting misalignment of the toggle mechanism, the dirty contacts and the debris prevented reliable electrical switching of the device and presented the opportunity for intermittently open electrical contacts.

June 2017
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