Incident Overview
On July 19, 2011, a SAAB 340 cargo aircraft operated by an unspecified carrier was preparing for a flight from Warsaw Chopin Airport (LROP) to Bratislava Airport (LZIB). During the takeoff roll on runway 08R at 06:06, the crew observed that the first officer's (F/O) airspeed indicator showed no reading. At 70 knots, the crew decided to reject the takeoff, informed the tower, and taxied back to the parking position.
First Maintenance Action
The aircraft was handed over to a mechanic who had flown with the crew on the previous day's flight, which had encountered heavy rain and icing conditions. Inspection of the pitot-static system revealed water in the system drains. After draining the system, the mechanic cleared the aircraft for flight. The crew started the engines and reported ready for departure. Taking the same runway, during the takeoff roll, the F/O's airspeed indicator again malfunctioned. The crew rejected the takeoff a second time and returned to the parking position.
Second Maintenance and Part Replacement
The mechanic again found water in the system drains. With support from the operator's technical department at the home base, a system tester and compressed nitrogen were ordered. The mechanic purged the system and performed tests, noting significant discrepancies between the standby airspeed indicator and the right airspeed indicator (ASI). The right ASI was removed and replaced with a new unit. The aircraft was then returned to service.
Continued Issues
On July 20, 2011, the crew reported for duty at 05:00 UTC and began takeoff on runway 08R at 05:57 UTC. Again, the F/O's airspeed indicator showed erroneous readings; it was functioning but indicating lower than the left ASI and standby indicator. The takeoff was rejected and the aircraft returned to the parking position. The technical personnel drained the system once more, again finding water, and performed a system test before clearing the aircraft. During a subsequent takeoff at 07:21, the F/O's airspeed indicator readings were correct, so the crew continued the takeoff and the flight proceeded without further issues. That day, the aircraft completed three additional flights without incident and returned to its home base at Wrocław Airport (EPWR) the same day.
Further Investigation and Final Incident
On July 21, 2011, the technical department inspected and purged the pitot-static system while the aircraft was at home base, finding no abnormalities. The next day, July 22, 2011, at 01:56, the aircraft taxied out at EPWR for a positioning flight. During takeoff in rain, the crew noticed irregularities in the right airspeed indicator: it showed 40 knots while the others showed 70 knots. The takeoff was rejected and the aircraft returned to the apron. The duty mechanic drained and purged the system with compressed nitrogen, then cleared the aircraft for flight. Subsequent flights occurred without further issues.
Examination of Removed Instrument
The airspeed indicator that had been removed at LROP was sent to the manufacturer for testing. The tests revealed that the instrument was out of calibration and required repair. The report did not describe the reasons for the de-calibration; therefore it cannot be ruled out that moisture ingress caused the de-calibration.
Probable Cause
According to the investigation, the incident was caused by significant water contamination in the pressure system supplying the first officer's airspeed indicator. The reasons for the water contamination were not conclusively identified. Additionally, the airspeed indicator was found to be de-calibrated. A probable cause is the possible improper use of the pitot tube cover.