Factual Information
On September 23, 2021, at about 09:14 Japan Standard Time, a Robinson R44 II helicopter (registration JA76EL) took off from a taxiway at Nagasaki Airport. The aircraft was operated by a private owner under an entrusted flight operation to Ogawa Air Co., Ltd. The captain, aged 39, held a commercial captain certificate for rotorcraft and had a total flight time of 2,374 hours 02 minutes. The flight was planned under visual flight rules from Nagasaki Airport to Kagoshima Airport for personnel transport.
The aircraft had requested departure instruction at 09:11 and was instructed to use Runway 32 and taxi to the runway holding point on Taxiway T2. While taxiing, the aircraft called the tower control position and was cleared for take-off with the phraseology "RUNWAY32 AT T2, CLEARED FOR TAKE-OFF" at 09:13. The captain read back the clearance but interpreted it as clearance to take off from Taxiway T2. The aircraft then took off from Taxiway T2, which is parallel to Runway 32, at about 09:14.
The tower observed the aircraft turning right on Taxiway T2 and became concerned due to its unusual movement. After visually recognizing the take-off from the taxiway, the tower re-issued the take-off clearance from Runway 32, but the captain continued climbing. The tower then instructed the aircraft in Japanese to take off from the runway, at which point the captain realized the mistake. The aircraft then made a left turn about 800 m ahead of Taxiway T2 and moved over Runway 32 to continue the flight.
The captain had been a contract pilot since April 2021, based at Kagoshima Airport, and was familiar with helicopter operations there. This was the captain's first flight operation at Nagasaki Airport. The captain was aware that Taxiway T2 at Nagasaki Airport did not have a helipad. However, when given the take-off clearance, the captain interpreted it as permission to take off from Taxiway T2, as the captain was accustomed to taking off from T2 Helipad at Kagoshima Airport, where a helipad is installed and published on Taxiway T2.
At Nagasaki Airport, the ATC Operational Guidelines stipulate that take-off and landing areas for helicopters under visual flight rules are runway or helipad. Helipads are installed in two locations on the parallel taxiway, but not on Taxiway T2. At Kagoshima Airport, a helipad is installed on Taxiway T2 near the helicopter apron.
The ATC Standards set by the Civil Aviation Bureau of Japan specify that for intersection departures, the intersection name should be included in the take-off clearance (e.g., "RUNWAY34 AT T2, CLEARED FOR TAKE-OFF"). For helicopter take-offs from areas other than the runway, the clearance should state the take-off area at the end (e.g., "CLEARED FOR TAKE-OFF FROM T2 HELIPAD"). The tower issued the clearance using the standard phraseology for an intersection departure.
Analysis
The Japan Transport Safety Board (JTSB) analyzed that the captain most likely expected to take off from T2 intersection at Runway 32 when instructed to taxi to the holding point. When the take-off clearance was issued promptly, the captain misinterpreted it as clearance to take off from Taxiway T2. The JTSB concluded that this misinterpretation was probable due to the captain's customary practice of taking off from T2 Helipad at Kagoshima Airport and the captain's failure to correctly recognize the difference between phraseologies for intersection departure and helipad take-off.
Probable Cause
The JTSB concluded that the probable cause was more likely the captain's misinterpretation that, when cleared for take-off from T2 intersection at Runway 32, the aircraft was cleared for take-off from Taxiway T2, leading to the take-off from the taxiway.
Safety Actions
On the day of the incident, the company reminded all employees that take-off from any area other than runway or helipad is not authorized.