Air North: the DC-3 / C-47 Era
The Transportation Safety Board of Canada (TSB) investigated this occurrence for the purpose of advancing transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.
The DC-3 aircraft, with the captain, first officer, and an apprentice aircraft maintenance engineer on board, was to be ferried from Vancouver, British Columbia, to Whitehorse, Yukon. Just after take-off from runway 08, as the first officer was setting the engine power, the right propeller began to over-speed. The captain told the first officer to shut down and feather the right engine. The first officer did as instructed, and advised the Vancouver tower controller of the engine problem and that they would return to the airport to land on runway 08.
The captain turned the aircraft to the right, onto downwind for runway 08; however, because the aircraft's altitude and airspeed were decreasing, the first officer advised the tower controller that theywouldlandonrunway30. Theaircraftcontinuedtoloseheight, narrowly avoiding buildings in its path, and crashed to the ground, one mile short of runway 30. The three occupants were seriously injured during the impact and the post-crash fire; the captain died of his injuries eight days after the accident.
Other Factual Information
The weather at the time of the occurrence was suitable for visual flight; the temperature was 20°C, and the wind was from 110 degrees magnetic at six knots.
The captain and the first officer were certified and qualified for the flight in accordance with existing rules and regulations. They were not working full time for the company; however, at one time they both had been employed as company check pilots on the accident aircraft type.
The aircraft had been operated on a two-year sub-charter by a Vancouver based company. The charter was complete, and the accident flight was to ferry the aircraft to the operator's main base at Whitehorse. While the aircraft was based in Vancouver, it was maintained in accordance with the operator's Maintenance Control Manual by a apprentice aircraft maintenance engineer (AME) under the supervision of a DC-3 endorsed AME. The aircraft's weight and centre of gravity were within limits on this flight.
Although the aircraft was partially destroyed by the post-crash fire, an examination of the wreckage confirmed the continuity of the flight controls, and that the landing gear and flaps were up at impact. Fuel samples taken from both engines indicated that the correct fuel was used.
There was no oil in the right engine's oil tank; a flange at the lowest point of the tank had been pushed in by impact forces and the oil had drained out. There was oil on the ground beside the right engine nacelle that might have drained from the tank, but the amount could not be quantified. The amount of oil on the ground and on the aircraft did not appear to account for the contents of a full oil tank. The right engine's oil tank was removed from the airframe, opened, and examined. The airframe-side oil hoses, shut-off valve, fittings, and oil cooler were examined. No malfunction or defects were found that would have precluded the normal circulation and distribution of engine oil.
Examination showed that, at impact, the right engine was not operating, the left engine's propeller was turning at about 2,700 rpm, and the left engine manifold pressure was about 54 inches. Take-off power settings are 2,700 rpm and 48 inches of manifold pressure.
The left engine was found to be capable of producing full power; however, there was some internal damage, consistent with operating the engine above its normal rated power. There was some internal damage to the right engine, consistent with inadequate lubrication during operation. No other discrepancies were observed that would have precluded its normal operation.
Examination of both propellers and the propeller domes revealed no defects. The right engine propeller constant speed unit and the feathering pump were found to be operable. The propeller shim plates were recovered. They revealed that the left propeller blade angle was about 26 degrees, normal for the power setting; the right propeller blade angle was about 60 degrees, 28 degrees less than fully feathered.
The flight crew were both aware that the oil consumption of the right engine had been high in the recent past. During his pre-flight inspection, the first officer checked the engines for visible oil leaks, and he checked the oil levels of both engines; there were no leaks and the oil quantities were sufficient. The crew flight planned for a stop in Prince Rupert, British Columbia, en route to Whitehorse for the sole purpose of checking the engine oil levels.
While still on the ramp, the flight crew ran up both engines in preparation for departure and, as the right engine was run-up, the first officer noted that the oil pressure was fluctuating within the normal range. The first officer and the apprentice AME said that they saw no signs of an oil leak before, during, or after the run-up, and that there was no oil on the ground in the area of the run-up. They reported that all other engine systems, including the propeller feathering system, operated normally during the run-up.
The first officer noted that right engine oil pressure was again fluctuating on take-off. When he reduced engine power after take-off, the right engine rpm increased from about 2,750, the maximum allowed, to over 3,300. The captain elected to shut down and feather the right engine because the over-speeding was uncontrollable. While the first officer was shutting down the right engine, the captain increased the power on the left engine to about 54 inches of manifold pressure because the aircraft was losing airspeed.
The aircraft's Pratt and Whitney engines (model R-1830-92) are equipped with Hamilton Standard (23E50-505) hydromatic, full feathering, constant speed, controllable pitch propellers. The propeller blades have a low pitch angle of 18 degrees, a full feather angle of 88 degrees, and an approximate constant speed operating range of 29 degrees. When the propellers are turning, centrifugal force acting on the blades tends to drive the blades towards the fine pitch stop. High pressure engine oil, metered by the constant speed unit (CSU) governor, counters the centrifugal force as required to maintain a constant propeller rpm. Should the CSU be deprived of oil, centrifugal force will drive the blades towards the fine pitch stop, and the propeller could over-speed. A high-pressure feathering pump, using engine oil, is incorporated to drive the blades to the full-coarse blade angle of 88 degrees for feathering. A standpipe, located in the oil tank, ensures a reserve of about two gallons of oil for propeller feathering.
The aircraft's left engine had been changed two months prior to the occurrence; its oil consumption was a normal half-gallon an hour. The right engine, which was near its overhaul time, was reported to consume up to two gallons per hour. Two days before the accident flight, the apprentice AME ran up both engines and discovered a major oil leak in the area of the crank case breather of the right engine. The engine was washed, topped-up with oil, run up several times, and topped-up with oil again; there were no more apparent oil leaks.
A climb performance analysis, based on the speed and altitude of the aircraft just before the crash and from air traffic control radar data, revealed that the aircraft's average rate of descent was about 250 feet per minute and the airspeed varied between 100 knots and 80 knots. The aircraft was approximately 600 feet above ground level at its highest point. The angle of bank during the right-hand turn toward the airport was 13 degrees and into the shut-down engine. The drag increase associated with this turn was calculated not to have significantly contributed to the loss of airspeed. The single engine rate of climb was calculated from the Aircraft Flight Manual data. Based on actual weather conditions and aircraft weight,the aircraft was capable of a rate of climb 400 feet per minute. Information provided by the manufacturer indicates that if the inoperative engine's propeller is not feathered the aircraft cannot maintain altitude.
The flight crew were aware of the right engine's history of oil consumption and oil leaks, and they planned to stop en route solely to check the oil quantity. Having had this concern, it is unlikely that the crew would depart Vancouver with less than full oil tanks.
The only aircraft system that appears to have malfunctioned is the right engine's oil system, as evidenced by interior engine damage typical of inadequate lubrication, the right propeller over-speed, and the failure of the right propeller to completely feather on shut-down. However,the Board was unable to determine the cause of the oil system malfunction.
Because the right propeller did not completely feather, the aircraft was not capable of maintaining level flight on one engine, and the captain was unable to prevent the aircraft from descending to the ground.
The following Engineering Branch reports were completed:
LP 116/95 Engines Examination
P 126/95 Aircraft Climb Performance Analysis LP 139/95 Propeller Blade Pitch Angle
LP 6/96 Propeller Feathering Pump
1. The flight crew were qualified for the flight in accordance with existing regulations.
2. The aircraft weight and centre of gravity were within limits.
3. The left engine and propeller were functioning normally.
4. No mechanical defects were found on the right engine, the right propeller, or their oil systems.
5. The right engine over-sped, probably because the CSU was deprived of oil.
6. The right propeller was not fully feathered at impact, probably because the feathering pump was deprived of oil.
7. The right engine exhibited internal damage typical of that caused by inadequate lubrication.
8. The aircraft was unable to maintain flight because of the drag generated by the windmilling right propeller.
Causes and Contributing Factors
The aircraft's right engine oil system malfunctioned for reasons that were not determined, and the right propeller did not completely feather during the emergency shutdown. The aircraft was unable to maintain flight because of the drag generated by the windmilling right propeller.
This report concludes the Transportation Safety Board's investigation into this occurrence. Consequently, the Board, consisting of Chairperson, John W. Stants, and members Zita Brunet and Maurice Harquail, authorized the release of this report on 30 May 1996.
This Transportation Safety Board of Canada (TSB) crash report has been reproduced in its entirety.