Accident Kawasaki BK 117B-1 B-77009,
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ASN Wikibase Occurrence # 161466
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Date:Wednesday 16 October 2013
Time:08:20 LT
Type:Silhouette image of generic BK17 model; specific model in this crash may look slightly different    
Kawasaki BK 117B-1
Owner/operator:Sunrise Airlines
Registration: B-77009
MSN: 1059
Year of manufacture:1990
Fatalities:Fatalities: 3 / Occupants: 3
Aircraft damage: Destroyed
Location:Jade Mountain -   Taiwan
Phase: Landing
Departure airport:Taipei Songshan Airport
Destination airport:Tataka
Investigating agency: ASC
Confidence Rating: Accident investigation report completed and information captured
A helicopter with two pilots and one passenger crashed during internal-cargo operations to support a weather station located in mountainous terrain.
The helicopter crashed 500 meters east of the Central Weather Bureau's observation station on Yushan, also known as Jade Mountain.

Findings related to probable causes:

1. Neither did the flight crew precisely calculate the aircraft loading, nor did the ground staff actually weight the loading at the sites, and the flight crew did not request ground staff to perform it. This above mentioned operation could not confirm and control the loading of the aircraft; therefore the gross weight may exceed the performance limits of the aircraft. Conservatively estimated the gross weight of the aircraft at the occurrence flight, it would exceed the limit of hover ceiling in ground effect on the flight manual. Based on the assessment of the aircraft manufacturer, the aircraft tail rotor performance may have been in a critical condition while it conducted the landing on the Yushan heliport.

2. The tail rotor control margin may have been in a critical condition when the occurrence aircraft was landing under overweight condition. Following the negative impact of inappropriate operation of the flight crew or the gust wind, it may lost the tail rotor effectiveness which then caused the aircraft yawing to the right. The cockpit voice recorder (CVR) and video indicated that the wind speed and direction at 0808:42.4 to 0808:56.7 time period were normal while the aircraft approaching to the Yushan heliport. The aircraft descended obviously at about 13 feet height above the heliport. At 0808:58.1 aircraft hovering about 3-4 feet height above the ground, it suddenly yawed to the right and rose aloft. This phenomenon may be caused by the flight crew rising the collective lever to control the rate of descent for landing. Due to the aircraft overweight, the tail rotor may not have sufficient thrust to balance the increased torque of the main rotor, and then following yawing to the right. At the same period, it may be also possibly affected by the gusts which severely increased the rate of rotation.

3. In accordance with the Federal Aviation Administration (FAA) AC90-95, the situation of occurrence aircraft (high gross weight, high altitude, high power, low air speed, right turning at landing phase, power increased) are either the conditions or factors which could conducive the unanticipated right yaw. There was no available information of wind speed and direction at occurrence site, but according to the video data, the aircraft suddenly yawing to the right, the unexpected gust wind may contribute the aircraft loss it tail rotor effectiveness.

4. The situation awareness and knowledge related to loss of tail rotor effectiveness of flight crew were insufficient which resulted in aircraft existing in situations that was prone to loss of tail rotor effectiveness. When the aircraft encountered the loss tail rotor effectiveness, there was probably no more rudder available to stop the right yawing even the flight crew applied full left rudder. When the aircraft off from the heliport, the flight crew probably was unable to take proper action to escape due to the aircraft rapid spinning and the surrounding terrain. Finally the aircraft was loss of control and crashed into terrain.

Accident investigation:
Investigating agency: ASC
Report number: 
Status: Investigation completed
Download report: Final report



Revision history:

16-Oct-2013 20:54 mcollins Added
17-Oct-2013 07:02 krasatpi Updated [Time, Aircraft type, Other fatalities, Departure airport, Destination airport, Source, Narrative]
17-Oct-2013 07:31 krasatpi Updated [Damage]
17-Oct-2013 07:49 TB Updated [Aircraft type, Registration, Cn]
17-Oct-2013 17:25 Anon. Updated [Registration, Cn, Source]
31-Oct-2014 19:11 harro Updated [Phase, Source, Narrative]
05-Jun-2021 14:26 harro Updated [Accident report]

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