Lithuanian investigators revealed that the flap of the Boeing 737-400 cargo ship remains withdrawn during the final approach to Vilnius.
About 10 minutes before the crash involving the Swiftair aircraft on November 25th last year, the cockpit voice recorder detected a “audible double click.” This coincided with the engine-driven pump and the electric pump of the hydraulic system “B”.
The “B” hydraulic system enhances several systems, including trailing edge flaps and Autopilot B.
Investigators said in a preliminary finding that the autopilot had been cut off and attempted to rekindle it. As a result, the assistant officer continued to fly the aircraft manually with AutoTrust active.
The captain spent time trying to contact the Vilnius approach control, but had to be corrected using the wrong frequency.
Approximately five minutes after the hydraulic system was turned off, the crew completed the approach checklist, but the landing checklist did not complete.
The first mate also asked if the engine's anti-ice was turned on, which the captain confirmed, but the flight data recorder indicates that the anti-ice is not activated. The engine anti-ICE switch is a direct switch on the overhead panel hydraulic system pump.
Both pilots realized what the aircraft needed to slow down. The captain extended the speed brakes and advised the assistant officer to raise his nose before the crew began to select a flap setting.
The flap handle has been moved, but flight data indicates that the flap did not unfold.
The aircraft entered the final approach at 2,700 feet, but the first mate asked for a “flap 15” and an extension of the landing gear, but the flap remained withdrawn.
According to the investigation, the captain said “it was still very fast and (the assistant officer) had to slow down first.”
After approach controls instructed the crew to contact the approximately 4nm tower from the runway, another radio mixing meant that the aircraft was neither the tower nor the frequency of approach.
When the captain made visual contact with the runway, he told the first mate again to reduce the speed.
Flight-Data recorder information shows an increase in the 737 pitch and its attack angle, and the assistant officer realized that the flap was still being withdrawn, just as when the aircraft's stick shaker was triggered and warned of a possible food stall.
The ground-mounted warning system also issued “sinkrate” and “pull-up” warnings.
The crew asked for a go-around, and the engine power began to increase, but a terrain warning sounded and the aircraft collided with the ground. Of the four residents, the captain was fatally injured, while the other three were seriously injured.
The Lithuania Transportation Accident Investigation Department has yet to reach a conclusion on the cause. National prosecutors have recently tried to raise questions to the surviving pilots after saying that the “activated hydraulic system” controlling the flaps probably led to crashing.
