Accident Overview
On December 8, 2023, a Daily Air (德安航空) Kawasaki BK117 helicopter, registration B-55507, was conducting an external load operation. The flight departed from the Tongfu temporary landing site in Xinyi Township, Nantou County at 0728 local time, tasked with resupplying the Guan Gao area along the Chenyoulan River. The crew consisted of two pilots: the pilot flying (PF) in the right seat and the pilot monitoring (PM) in the left seat. While performing an engine power check near the 209 forest compartment, the crew noticed that the slung load had detached unexpectedly. They immediately decided to return and landed at Tongfu at 0748. The crew and aircraft were safe.
Investigation Findings
The Taiwan Transportation Safety Board (TTSB) investigated the incident. The investigation examined potential causes for the unintended release, including electrical release circuit anomalies, manual mechanical issues, and improper shackle use—all of which were ruled out. The possibility of inadvertent activation of the cargo hook release switch by the crew could not be confirmed. The report noted that the flight crew did not follow standard operating procedures (SOPs) and standard callouts during the external load operation, which increased the risk of inadvertent release and compromised situational awareness. Additionally, deviations from SOPs were not communicated between crew members, indicating inadequate crew resource management.
Risk-Related Findings
Common non-compliance with SOPs among Daily Air BK117 pilots regarding arming the cargo hook before takeoff was identified, suggesting an unsafe culture. Daily Air's internal audit mechanisms failed to detect such deviations, and the Civil Aeronautics Administration's oversight was also limited due to the difficulty of conducting in-flight checks during special operations. Discrepancies between different Daily Air manuals (Aircraft Operating Manual, External Load Operations Manual, and Flight Crew Training Manual) regarding sling load procedures created potential for inconsistent execution. The use of webbing slings as cargo straps caused significant vibration during flight, affecting handling.
Other Findings
Both pilots held valid licenses and medical certificates; no medical, drug, or alcohol factors were found. The aircraft's weight and balance were within limits, and preflight airworthiness information showed no anomalies.