Trans-Canada Air Lines Flight 304

Trans-Canada Air Lines

Industry	Airline
Founded	April 1, 1937 (1937-04-01) in Canada
Headquarters	Canada
Products	Air transportation

Trans-Canada Air Lines Flight 304 involved a Vickers Viscount 700 series aircraft operated by Trans-Canada Air Lines. On July 9, 1956, during a flight from Chicago, Illinois to Toronto, Ontario and continuing to Montreal, Quebec, the aircraft’s No. 4 propeller detached from its engine while flying over Flat Rock, Michigan in the United States. A single propeller blade penetrated the passenger cabin, resulting in the death of one passenger and injuries to four other passengers as well as one flight attendant. The crew diverted and successfully performed an emergency landing at Windsor, Ontario. This incident marked the first occurrence of propeller separation on a turbo-prop aircraft in scheduled service and was also the initial accident involving a Vickers Viscount.

Aircraft background

Trans-Canada Air Lines was the pioneer among North American carriers to receive the Viscount aircraft. Unlike traditional piston engine airliners such as the Douglas DC-6 and the Lockheed Constellation frequently used by North American airlines at that time, the Viscount was known for its quieter operation and minimal engine vibration. Its Rolls-Royce Dart engines delivered smoother performance compared to piston engines, leading Vickers engineers to consider propeller detachment an unlikely event.

Accident details

On the morning of July 9, while cruising at an altitude of flight level 190 over Flat Rock, Michigan, the aircraft’s No. 4 engine experienced a sudden RPM drop followed by an overspeed reaching approximately 14,000 RPM—well above normal cruise levels. Attempts by the flight crew to feather the propeller were unsuccessful as the engine RPM continued rising and airspeed decreased. The pilots declared an emergency and initiated an immediate descent while depressurizing the cabin. Shortly after descending through 9,000 feet, the propeller separated from the No. 4 engine. One blade penetrated through the cabin wall and seats in the first row, fatally wounding a young woman travelling with two small children. Additionally, three members of another family seated across the aisle and a flight attendant standing near the front of the cabin sustained injuries. The victim’s children were unharmed. The aircraft landed safely at Windsor; only after touchdown did crew become aware of casualties inside the cabin. A small fragment of the blade remained lodged inside, while the main portion along with the remaining three blades were recovered near Flat Rock.

Investigators from Canada determined that failure of a bevel gear within the oil pump drive caused loss of lubrication to the propeller mechanism. This failure led to decoupling of the propeller from its engine drive shaft, allowing it to windmill uncontrollably at high speed. During their emergency descent, pilots allowed airspeed to approach maximum limits which likely placed excessive stress on the windmilling propeller contributing to its in-flight failure. The potential for bevel gear failure resulting in propeller windmilling had not been anticipated by Vickers engineers and was consequently absent from both training materials and operational manuals.

This accident prompted manufacturers and engineers to reconsider prior assumptions that turbo-prop aircraft were inherently less susceptible to propeller separation incidents.

Aircraft

The aircraft involved was a four-engine Vickers Viscount model, which initially took to the skies in the United Kingdom in 1955. It was originally delivered to Trans-Canada Air Lines on 21 June 1955. In January 1964, the plane was acquired by a private American owner before being transferred to Air Inter in France in June 1965. The aircraft was retired from service at Orly Airport in October 1974 and subsequently dismantled and scrapped throughout 1975.

References

Notes

Sources

• "'Flying' Prop Kills One, Injures Five". The Deseret News. Salt Lake City, UT. UP. July 10, 1956. p. 4. Retrieved July 23, 2014.
• "Propeller Tears Loose, Kills Passenger Aboard Airliner". The Wilmington News. Wilmington, NC. AP. July 10, 1956. p. 1. Retrieved July 23, 2014.
• "Propeller Flies Off, Kills One". The Gazette. Montreal, Quebec. CP. July 10, 1956. p. 1. Retrieved July 23, 2014.
• "Propeller slices through plane". The Argus. Melbourne. July 11, 1956.
• "Woman Killed By Piece Off Propellor". The Canberra Times. Canberra. AAP - Reuters. July 11, 1956.
• Durfree, James R; Gurney, Chan; Denny, Harmar D; Minetti, G. Joseph (1957). CAB Accident Investigation Report: Trans-Canada Air Lines Viscount, CF-TGR, Flat Rock, Michigan, 9 July, 1956. United States Civil Aeronautics Board.
• Eastwood, Tony; Roach, John (1990). Turbo Prop Airliner Production List. The Aviation Hobby Shop. ISBN 0-907178-32-4.
• Knight, Clayton; Knight, K. S. (1958). Plane Crash: The Mysteries of Major Air Disasters and How They Were Solved. Greenberg Press.
• Job, Macarthur (2001). Air Disaster, Vol. 4: The Propeller Era. Australia: Aerospace Publications Pty. Ltd. ISBN 978-1-875671-48-9.

External links

• Report - Civil Aeronautics Board - PDF
• Accident details from airdisaster.com database
• Accident information at Aviation Safety Network