Accident Overview
On November 7, 2015, a Beech Super King Air 350 aircraft, registration NA-302, operated by the National Airborne Service Corps (NASC), was conducting an aerial survey and mapping mission over the Nantou to Miaoli Houlong area. The crew consisted of a pilot-in-command, a copilot, and two aerial survey operators. The aircraft departed Taichung/Ching Chuan Kang Airport at 1034 local time and returned to the airport around 1310.
During the initial approach, the landing gear indicator lights showed only the nose gear light illuminated. The crew executed a go-around. On a subsequent approach, after extending the landing gear, only the left main gear indicator light failed to illuminate, but the landing gear handle lock appeared engaged. The crew concluded that the indication issue was due to a faulty bulb. After receiving landing clearance, the crew extended the flaps to the full position, which triggered a landing gear warning horn. The horn persisted until touchdown.
Upon touchdown, the left and right main landing gear and the nose gear abnormally retracted, causing the aircraft to slide on its belly to a stop. Post-accident inspection revealed damage to the left and right main gear doors, left and right engine nacelles, left and right flaps, and left and right propellers.
Findings
The investigation identified that the 2-amp circuit breaker controlling the landing gear power pack was found in the tripped position, indicating a loss of electrical power to the hydraulic pump during approach. This prevented the landing gear hydraulic system from building pressure. As a result, the landing gear did not reach the down-and-locked position when the crew operated the gear lever.
Despite anomalous gear indications and the activation of the landing gear warning horn when flaps were extended, the flight crew misinterpreted these as false signals. They did not follow the aircraft manual's procedures for manual gear extension. The crew's understanding of the landing gear system and warning system was found to be insufficient, and crew resource management was ineffective in addressing the abnormal situation.
Probable Cause
The landing gear power circuit breaker was tripped, preventing hydraulic pressure buildup; the landing gear did not reach the down-and-locked position; the crew misinterpreted the gear warning indications as false and did not execute the manual gear extension procedure.