Introduction
On the afternoon of the accident, a Keystone Air Service Ltd. Piper PA-31-350 Chieftain (serial number 31-7752107) was conducting an instrument flight rules flight from Pukatawagan, Manitoba, to Winnipeg, with a refuelling stop at Flin Flon. The aircraft carried one pilot and seven passengers.
Sequence of Events
The flight departed Flin Flon with full fuel tanks. At 1741 central standard time, while conducting an instrument landing system approach to runway 36 at Winnipeg International Airport, radar contact and radio communication were lost. The airport crash alarm was activated, and emergency services initiated a search. A passenger called 911 via cellular phone to report the crash. Winnipeg city police located the aircraft about an hour later in a wooded area approximately two nautical miles south of the airport.
Two of the eight occupants sustained serious injuries; several others had minor injuries. The aircraft was substantially damaged, and there was no post-crash fire.
Weather Conditions
At the time of the accident, the weather at Winnipeg airport was: temperature 2°C; wind 010° magnetic at 22 knots, gusting to 30 knots; overcast clouds at 500 feet above ground; visibility 3 statute miles in light rain and mist. Icing in cloud was not observed or reported by landing aircraft.
Pilot Information
The pilot held a valid commercial pilot licence with a Group 1 instrument rating. He had completed a pilot proficiency check in September 2000 and met recency and currency requirements. Total flight time was approximately 1500 hours, with about 200 hours on the accident aircraft type. He had flown about 47 hours in the last 30 days, including 19 hours in the last 7 days, and had a day of rest before the occurrence. At the time of the accident, he had been on duty about 10.5 hours, with 4.6 hours of flight time. The flight was conducted under Canadian Aviation Regulation 703 (Air Taxi Operations), and the aircraft was certified for flight into light-to-moderate icing conditions.
Approach and Engine Failure
Radar data showed the aircraft was in instrument meteorological conditions at 2500 feet above sea level (asl) on radar vectors when cleared for a straight-in ILS approach to runway 36. The pilot descended to 2200 ft asl to intercept the localizer, then gradually descended to 1900 ft asl 1.5 miles before the Whiskey beacon (final approach fix, minimum crossing altitude 2000 ft asl, glidepath check altitude 2110 ft asl). Until reaching the beacon, the pilot maintained 105-110 KIAS. The aircraft's indicated airspeed then decreased to 80-90 KIAS before crossing the beacon, further reducing to 70-80 KIAS after descending to 1700 ft asl. The landing gear were extended and flaps in approach setting.
Near the Whiskey beacon, the right fuel flow warning light illuminated. The pilot confirmed fuel boost pump switches ON and main fuel tanks selected, and observed the right main tank at three-quarters full. About 20 seconds after crossing the beacon, the aircraft yawed suddenly to the right when the right engine lost power. The pilot rechecked boost pump and fuel selector switches and attempted a restart, but this delayed the basic emergency response.
The pilot then performed an engine-out drill: increasing power on the left engine, raising the landing gear, and feathering the right engine, but left the flaps in approach setting. Raising flaps was likely essential to reach the runway, but could not be done safely until airspeed increased. The stall warning tone sounded repeatedly. When left engine power was increased, the aircraft yawed and rolled right; the pilot countered by reducing power. The aircraft descended through cloud base at an average of 800 ft/min at about 80 KIAS. The pilot selected landing gear down and retarded left throttle to idle as the aircraft settled into trees.
Post-Crash Examination
The aircraft came to rest upright with gear down and flaps partially extended. The right inboard fuel cell was ruptured; a considerable amount of aviation fuel remained in the right surge tank. A globule of ice (approximately one cup of water when melted) was removed from inside the right surge tank. The left inboard tank was about three-quarters full; some fuel had escaped through an impact-damaged drain. Cockpit fuel selector switches were at the inboard position. All four fuel caps were securely fastened.
Each inboard fuel tank has a small surge tank (about 4 gallons) with a one-way flapper valve from the large segment. Analysis showed the right fuel flow warning light was on at impact. A rust line on the large segment of the right tank indicated water had reached the level of the flapper valve. Tests at the regional Transportation Safety Board office showed that water could freeze and immobilize the flapper valve in the closed position.
The right engine was examined and test run with no pre-impact anomalies. The left engine's turbocharger was jammed, but likely due to impact; no pilot-noticed power differential occurred during flight.
Probable Cause
It is probable that the water froze around the one-way flapper valve in the right inboard tank, obstructing the flow of fuel into the surge tank. When the inboard tanks were selected, the fuel in the surge tank was quickly depleted, the low-fuel sensor activated the right fuel flow warning light, and the right engine stopped because of fuel starvation.