Cessna 402C N121PB accident near Watertown, New York

Probable cause

The pilot's decision to continue the approach with a known anomaly with the left airspeed indicator. Contributing to the accident was an undetermined malfunction of the left airspeed indicator and the condition of the runway, resulting in decreased braking capability.

NTSB analysis

The pilot of the scheduled passenger flight was conducting a visual approach to runway 25 at the destination airport in marginal visual meteorological conditions. As the airplane descended to the traffic pattern, the pilot noticed the airspeed decrease from 145 knots to 85 knots. The pilot applied full power but did not observe an increase in airspeed. He elected to continue the approach and, due to weather conditions, joined the traffic pattern for runway 7. It is likely that the pilot felt pressure to complete the flight due to the deteriorating weather conditions, rather than taking time to identify and correct the anomaly or to attempt to cross-reference with other instruments. When the pilot deployed the wing flaps and extended the landing gear, he noted that the airplane felt as though it was traveling faster than its indicated airspeed. The airplane touched down approximately 1,000 feet past the runway threshold and bounced. The pilot attempted to apply brakes, but reported that the braking action was "nil" due to runway contamination. The airplane continued down the runway, departed the paved surface, and came to rest 366 feet past the runway’s end. Postaccident testing revealed that the pitot tubes were warm to the touch when the pitot heat switch was turned on. Unregulated air pressure was applied to the right pitot tube and to the left pitot line downstream of the tube. The corresponding airspeed indicators displayed needle movement with no leaks detected. Since no further examination of the pitot-static system was conducted, the cause of the airspeed anomaly could not be determined.

Text from the NTSB. Open the NTSB docket for ERA10LA128 for the full record.