On August 17, 2003, a Bell 204B helicopter was involved in forest fire suppression at Bonaparte Lake, B.C. At about 11:05 Pacific Daylight Time (PDT), the helicopter departed a staging site, eastbound, slinging an empty water bucket on a 100-ft longline. Shortly after takeoff, the helicopter emitted a high-pitched, oscillating sound. The flight path and behaviour of the helicopter were normal as it went out of view over some trees. Immediately thereafter, there was a pronounced slap sound of the main rotor blade, followed by sounds of impact with the trees. The helicopter struck the ground just short of a small clearing adjacent to a fire road, about 0.25 NM southeast of the staging site. A post-impact fire ensued, which destroyed the helicopter. The main driveshaft assembly remained attached to the engine and transmission input quill assembly. The water bucket was found in a tree, detached from the longline, on the approach to the accident site. The longline was wrapped around another tree and lay in a direct line to the helicopter. The pilot was fatally injured.

Findings as to causes and contributing factors

1.        An imbalance of the engine compressor rotor assembly developed during the operation of the engine, resulting in contact between the rotor and stator assemblies. The contact led to the destruction of the compressor rotor assembly and engine failure. No conclusion could be reached with respect to the mode of failure that caused the imbalance.

2.        The combination of altitude, terrain features and the trailing longline, negatively affected the pilot’s ability to complete a successful emergency landing in autorotation.

Findings as to risk

1.        Some procedures used in the engine overhaul process were not in accordance with the manufacturer’s overhaul manual; failure to comply with the manufacturer’s instructions could compromise the integrity of the assembly and result in failure.

2.        Field adjustments to the engine fuel control takeoff trim without the confirmation of an N1 topping check for accuracy, introduce a risk of frequent or continuous operations at gas generator speeds and internal temperatures beyond established limits.

3.        An inconsistent placement of the external cargo release switch increases the risk of pilot confusion during an emergency when trying to activate the external cargo hook-release mechanism, possibly complicating an emergency landing.

4.        The foot pedal backup quick release is an approved system. However, its effectiveness is reduced because it requires the pilot to take one foot off of a primary flight control in an emergency.

Safety action taken

In December 2003, a Federal Aviation Administration (FAA) inspection of the engine overhaul company’s facilities and procedures was conducted. It was determined by the FAA that, at the time of the inspection, the inspectors “[were] confident that the company [had] the data, experience and knowledge to properly overhaul the engines for which they are rated.”

All Canadian operators of the T5311B engine were advised of the safety concerns identified during the overhaul process at the company’s facilities.

The helicopter operator has standardized the cyclic grips in all of its aircraft (excluding the Robinson 44s, which are incompatible for such a modification), so that the switches are the same in each type. It has also moved the emergency (manual) release to the collective in its Eurocopter AS350 and is searching for supplemental type certificates (STC) applicable to the rest of its fleet. The rationale is that the emergency-release systems (isolated pull handles or foot pedals) in the other aircraft also require the use of either hands or feet for operation; therefore, requiring the pilot to let go of a flight control in order to release an external load via the emergency release. With the manual release on the collective, activation is possible without requiring pilots to remove their hands or feet from primary flight controls.