What happened
On March 1, 2009, at 16:20 UTC, a Boeing 737-347, registration VP-BBL, operated by Atlant Soyuz Airlines, experienced an excursion from taxiway A at Brno Tuřany Airport (LKTB).
The aircraft was initially parked at apron M. After receiving clearance to start engines, the pilot successfully started engine number one. Following the engine start, the pilot requested departure information and was informed by ATC that the departure would be from runway 10.
While attempting to taxi toward taxiway A, the aircraft moved without having requested or received taxi clearance. During this movement, the aircraft failed to reach the intended heading of 275° and veered off the paved surface onto the grass on the southern side of taxiway A. The crew ceased radio communications with the tower once the excursion began. After realizing the aircraft was off the taxiway, the pilot shut down engine number one. Passengers were evacuated via stairs, and no injuries were reported among the 93 passengers or the 8 crew members.
The investigation
The ÚZPLN investigation examined the aircraft's systems, the pilot's actions, and the airport environment. Investigators found that the pilot was fully qualified and familiar with the Brno airport layout. The weather conditions were favorable, with good visibility and dry runway surfaces.
Upon inspecting the aircraft's cabin, investigators discovered that circuit breakers for the hydraulic pump electrical circuits on panel P6-2 had tripped. The investigation also looked into the functionality of the nose gear steering and braking systems. While the pilot had begun taxiing without ATC permission, the investigation focused on why the aircraft could not be steered or stopped as intended.
Findings
- The primary cause of the incident was the tripping of circuit breakers in the electrical circuits for the hydraulic pumps, which supplied the nose gear steering and braking systems.
- The loss of electrical power to these pumps led to a rapid decline in hydraulic pressure, rendering the steering and brakes ineffective.
- The pilot initiated taxiing from apron M without obtaining the necessary taxi clearance from ATC.
- The aircraft's movement could not be controlled or halted by the crew due to the simultaneous loss of steering and braking capability caused by the technical failure.