What happened
On January 7, 2009, an EC 120B Colibri helicopter, registration CS-HEX, was involved in a runway incursion at Cascais Aerodrome (LPCS). The aircraft, operated by Heliportugal, was performing an operational flight with one pilot and two passengers.
While maneuvering within the aerodrome movement area, the pilot was performing an air-taxi from parking position 'E' to taxiway 'J'. Because the helicopter was configured with skids, the pilot landed the aircraft at the intersection of taxiways 'J' and 'W' to safely change radio frequencies. During this process, the pilot established contact with the Tower controller.
Upon receiving instructions from the Tower to 'hold short of the runway', the pilot misinterpreted the command. The pilot believed the instruction authorized the aircraft to move closer to the runway, leading the helicopter to cross the vertical projection of the runway holding position and enter the runway protection zone. The Tower controller, noticing the incursion, immediately instructed an aircraft on approach to execute a missed approach and alerted the pilot of CS-HEX that they were interfering with the runway. The pilot promptly reversed the maneuver and returned to taxiway 'J'.
The investigation
The GPIAAF investigation examined the communications between the pilot and the air traffic control units (Ground and Tower). The investigation found that the initial communications between the pilot and Ground were conducted in Portuguese. However, the Tower controller's initial instructions to the pilot were delivered in English and at a very high rate of speech, making them difficult to perceive.
While the pilot performed a correct readback after the Tower repeated the instruction more slowly, the pilot's interpretation of the phrase 'hold short' was flawed. The pilot stated that the word 'hold' implied movement, and further noted that they initially understood the instruction as 'stop', which contributed to the confusion. The investigation also noted that the pilot, while experienced in scientific missions in Africa, was less familiar with the specific operational environment of Cascais Aerodrome.
Findings
- The primary cause of the incident was the pilot's deficient interpretation of the Tower's instructions.
- The Tower's initial 'hold short' instruction was transmitted too rapidly for the pilot to clearly understand.
- The pilot interpreted the 'hold short' instruction as an authorization to approach the runway rather than an instruction to remain behind the holding point.
- The pilot's landing at the taxiway intersection to change frequencies, while intended to prioritize safety during a high-workload phase, placed the aircraft in a position where the subsequent instruction was misunderstood.
- The aerodrome lacks published specific procedures for helicopter air-taxi, take-off, and landing operations.