What happened
On 22 November 1996, a King 56 departed Portland IAP at 1720 PST, operating under instrument flight rules for an overwater navigation evaluation toward North Island Naval Air Station. The flight proceeded normally through takeoff and climbout. Approximately 84 minutes into the flight, while cruising at FL 220, the flight engineer noted torque fluctuations on the number 1 engine.
Following this initial observation, the stability of all four engines degraded over a three-minute period, eventually leading to total engine failure. In response to the unfolding emergency, the engineer requested that the number 1 propeller be set to mechanical governing. The pilot subsequently ordered all four propellers to be placed in mechanical governing to manage what appeared to be a multi-engine rollback. During this period, the crew declared an in-flight emergency with Oakland ARTCC and altered course toward Kingsley Field in Klamath Falls, Oregon.
The radio operator also notified the USCG Humboldt Bay Station of the emergency. As the aircraft turned toward the coast, the number 3 and number 4 engines briefly regained some torque, but as the RPM on the number 3 engine fell below 94%, the final generator failed due to low frequency. By 1846 PST, the aircraft had lost all electrical power, leaving only the battery bus functional. The aircraft then entered a glide toward a ditching attempt.
During the sequence, the outboard wing sections and all four engines detached from the center wing section, which then separated from the fuselage. The engines and fuselage sank to the ocean floor at a depth of roughly 5500 feet. The wing sections remained buoyant for several days before sinking approximately 50 nm from the site of the impact. The accident resulted in 10 fatalities and one survivor.
Findings
- The flight experienced a progressive failure of all four engines following an initial torque fluctuation on the number 1 engine.
- Total loss of electrical power occurred when the final generator dropped offline due to low frequency following the decline of the number 3 engine's RPM.
- Structural failure occurred during the event, causing the separation of the engines, outboard wings, and fuselage.