What happened
On July 19, 2011, a SAAB 340 operated a cargo flight from LROP to LZIB. During the initial takeoff roll on runway 08R, the crew observed that the co-pilot's airspeed indicator was not providing readings. At a speed of 70 knots, the crew decided to abort the takeoff and returned to the parking stand.
Prior to this flight, the aircraft had arrived at LROP the previous day during heavy rain and icing conditions. Upon inspection, a mechanic found water in the system drains. After draining the lines, the aircraft was cleared for flight. However, during the subsequent takeoff attempt, the same lack of airspeed indication on the co-pilot's side was observed, leading to another aborted takeoff.
Following the replacement of the instrument with a new unit, a third takeoff attempt on July 20, 2011, resulted in erroneous, low airspeed readings on the co-pilot's side. After further draining and testing, a fourth takeoff attempt was successful, and the flight proceeded without further incident.
On July 22, 2011, during a repositioning flight at EPWR in rainy conditions, the crew again encountered discrepancies, with the right airspeed indicator showing 40 knots while other instruments indicated 70 knots. The takeoff was aborted, and the system was drained and blown out with nitrogen by the duty mechanic.
The investigation
The investigation focused on the recurring presence of water in the pitot-static system drains and the subsequent instrument failures. The decommissioned airspeed indicator was sent to the manufacturer, where tests confirmed that the instrument was out of calibration and required repair. The investigation could not definitively rule out that moisture ingress contributed to this decalibration.
Findings
- The primary cause of the incident was significant water contamination within the pitot-static system supplying pressure to the co-pilot's airspeed indicator.
- The airspeed indicator itself was found to be out of calibration.
- The improper use of Pitot tube covers was identified as a probable contributing factor to the system contamination.