Incident Overview
On Saturday, November 16, 2013, a Cessna TU206G, registered JA4000, operated by Honda Airways Co., Ltd., was conducting an aerial survey over Akita Prefecture, Japan. The aircraft, with a pilot and a passenger on board, departed from Honda Airport in Saitama Prefecture at 09:09 Japan Standard Time (JST). After completing photography over Yurihonjo, the aircraft climbed toward Noshiro City. At about 11:27, while at an altitude of 6,500 ft, the pilot noticed the oil pressure gauge indication slightly below 30 psi, outside the normal range. The pilot decided to divert to Odate Noshiro Airport but later changed to Akita Airport due to weather and equipment issues. At approximately 11:40, engine vibration occurred, and the pilot requested an emergency landing. The engine halted at about 11:43 JST, and the pilot made a forced landing at the site of the closed Akita Airport in Akita City. The aircraft sustained slight damage; no one was injured.
Sequence of Events
According to air traffic control communication records, GPS data, and statements from the pilot, passenger, and maintenance engineer, the flight history is as follows: At 11:03, the pilot reported to Akita Tower at 3,700 ft south of Akita Airport. By 11:27, the aircraft was abeam of Akita Airport at 6,500 ft. The pilot reported engine trouble to Sendai Flight Service Center at 11:28 and changed destination to Odate Noshiro Airport. At 11:30, the aircraft began descent. At 11:37, the pilot requested landing at Akita Airport. At 11:40, the pilot reported low oil pressure and engine vibration at 2,700 ft. At 11:41, emergency landing clearance was requested and issued. At 11:42, the pilot reported a forced landing to the seacoast. The aircraft descended and landed at the closed Akita Airport at 11:43.
Aircraft Examination
Post-incident examination revealed that the engine had lost oil due to a detached hose connecting the oil gage rod housing and the housing extension. The hose clamp was found out of position, toward the end of the hose, resulting in inadequate clamping. Engine vibration transmitted through the loose connection caused the hose to detach, leading to oil leakage and eventual engine failure. The aircraft's oil level had been full (12 quarts) before departure.
Probable Cause
It is probable that this serious incident occurred due to the fact that the engine of JA4000 continued to be operated in a state where the oil was leaking and had become insufficient; accordingly, the engine was broken, leading to engine halt in flight. It is probable that the cause of the oil leakage was due to the fact that engine vibration was being transmitted to the loose connection between the hose of the housing extension and the oil gage rod housing on the engine body, and then the hose detached from the housing. It is somewhat likely that the hose had come loose at the connection to the oil gage rod housing because the hose clamp had been installed in a state where it was out of position toward the end of the hose and jutted out toward the engine body; accordingly, uniform and adequate clamping of the hose was not achieved.