Occurrence
On June 13, 2008, at approximately 1140 Central Standard Time, a Cessna 337D (registration C-GYHW, serial number 337-1111) operated by Meadow Air Limited made a forced landing in a swampy area on the east shore of Churchill Lake, Saskatchewan, after a dual engine power loss. The aircraft was returning to Buffalo Narrows from Stony Rapids, Saskatchewan, following a passenger drop-off. The pilot declared an emergency about 14 miles northeast of Buffalo Narrows airport. The aircraft was substantially damaged. The pilot was transported to hospital in Île-à-la-Crosse and subsequently released with minor injuries.
Aircraft and Pilot Information
The aircraft was contracted to the Saskatchewan Government Ministry of Environment for forest fire detection. The operator owned two other Cessna 337s and had operated the type for several years. On June 12, 2008, the aircraft was fully refueled and completed a 0.9-hour training flight. It was not refueled before departing for Stony Rapids on June 13, as the pilot believed there was sufficient fuel for a round trip.
The pilot held valid certification and qualifications. He had accumulated 1100 total flying hours, including approximately 10 hours on the C-337 type, all from initial training. He was a new hire and the occurrence flight was his first operational trip on the C-337 with Meadow Air. He had been on duty for five hours at the time of the event.
Fuel System and Mismanagement
The C-337D fuel system includes two outboard main tanks and two inboard auxiliary (aux) tanks. Auxiliary fuel pumps can only draw fuel from the main tanks. To access auxiliary tank fuel, the pilot must first burn off one hour of fuel from the main tanks and then select the auxiliary tanks; this prevents return-line fuel venting. The main tanks hold 92 gallons, and the aux tanks hold 36 gallons, for a total of 128 gallons. Cruise power fuel consumption is about 18 US gallons per hour, but training flight consumption can be up to 25 gph.
The flight to Stony Rapids was uneventful. About 1 hour and 30 minutes into the return flight, the front engine lost power, followed shortly by the rear engine. The pilot switched both fuel selectors to auxiliary tank positions and turned on auxiliary boost pumps, but the engines did not restart. The main fuel tanks were found empty; both auxiliary tanks were full. The pilot had not used auxiliary fuel prior to the power loss because he believed enough fuel remained in the main tanks. Total flight time since refueling was about 4.5 hours.
Investigation Findings
Examination of the wreckage revealed no pre-accident anomalies. Propeller damage indicated the engines were not operating at impact. The investigation found that the pilot's fuel estimate for the round trip was inaccurate, leading to main tank depletion. The pilot did not understand the correct procedure to access auxiliary tank fuel; his operation of the fuel system rendered the auxiliary fuel unusable after the main tanks were empty. The operator's training program for the C-337D did not establish or test knowledge of fuel system operation, including auxiliary tank procedures. Several similar fuel management occurrences for this aircraft type were noted. The design and nomenclature of the fuel system (e.g., 'aux' pumps that cannot draw from aux tanks) can complicate operation during high workload.
Probable Cause
The Transportation Safety Board's investigation identified as causes and contributing factors: the pilot's inaccurate estimates of fuel remaining and required for the flight, leading to fuel exhaustion; the pilot's incomplete understanding of the aircraft's fuel system, which prevented use of auxiliary tank fuel after main tank depletion; and the operator's training program failing to establish adequate knowledge of fuel system operation.