Engine failure leads to hard landing in Alberta

Casualties unknown • Manning, Alberta 75 nm NE, CA

A Bell 204B helicopter experienced a sudden loss of engine power during a seedling delivery operation in Wadlin Lake, resulting in a heavy impact and serious injuries to the pilot.

What happened

At approximately 14:20 mountain daylight time, a Delta Helicopters Ltd. Bell 204B helicopter, registration C-GTNP, was performing slinging operations near Wadlin Lake, Alberta. The aircraft was descending to position a load of tree seedlings, attached to a 15-foot longline, when the pilot heard a scraping noise and felt a vibration. Immediately following this, the engine lost power, causing the helicopter to descend rapidly. During the descent, the cargo load struck the ground first, followed by the aircraft impacting the terrain approximately 80 feet beyond the load. The pilot sustained serious, but non-life-threatening, injuries and was rescued from the site later that evening.

The investigation

Investigators examined the Lycoming T53-11B engine and discovered that two blades had separated from the power turbine disc. This separation caused extensive damage to the turbine nozzle, shrouds, and other blades. Specifically, blade No. 1 fractured at the disc platform due to a pre-existing fatigue crack, while blade No. 52 fractured due to a separate fatigue crack; the second blade was subsequently damaged by debris from the first failure. While the exact origin of these cracks could not be identified through electron microscope examination, no evidence of corrosion, manufacturing defects, or mechanical nicks was found.

Technical analysis also reviewed the aircraft's weight and performance. At the time of the accident, the helicopter was carrying approximately 3,775 lb of cargo. While the total weight was within the modified maximum gross weight limits for the aircraft, it exceeded the maximum allowable weight for a hover out-of-ground-effect.

Findings

  • The engine failure was caused by the overstress extension of pre-existing fatigue cracks in two power turbine blades.
  • The loss of engine power occurred at a low altitude and low airspeed.
  • The aircraft was operating at a weight that exceeded the maximum out-of-ground-effect hover weight.
  • The combination of low altitude, the attached load, and the aircraft's position on the height-velocity (H-V) diagram contributed to the severity of the impact, as the decaying rotor speed left the pilot with insufficient kinetic energy for control.

Probable cause

The engine failed due to the fracture of two turbine blades caused by the expansion of pre-existing fatigue cracks. The severity of the resulting hard landing was compounded by the aircraft operating at a weight exceeding its out-of-ground-effect hover limit and within a critical area of the height-velocity chart.

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Frequently asked questions

What happened in the 2003-07-13 Bell 204B C-GTNP accident near Manning, Alberta 75 nm NE, CA?

A Bell 204B helicopter experienced a sudden loss of engine power during a seedling delivery operation in Wadlin Lake, resulting in a heavy impact and serious injuries to the pilot.

What aircraft was involved and where did it happen?

The accident on 2003-07-13 involved a Bell 204B C-GTNP, operated by Delta Helicopters Ltd., at Manning, Alberta 75 nm NE, CA.

What was the probable cause of the accident?

The engine failed due to the fracture of two turbine blades caused by the expansion of pre-existing fatigue cracks. The severity of the resulting hard landing was compounded by the aircraft operating at a weight exceeding its out-of-ground-effect hover limit and within a critical area of the height-velocity chart.

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