Tail rotor failure blamed for fatal 2019 game capture chopper crash

16 November 2021 - 16:15
The burnt-out wreck of the Bell 47 helicopter shortly after the crash. File photo.
The burnt-out wreck of the Bell 47 helicopter shortly after the crash. File photo.
Image: Supplied

The 2019 crash that killed a veteran game capture pilot and left his passenger severely injured and traumatised was caused by a tail rotor failure, according to a SA Civil Aviation Authority (Sacaa) investigation.

Pilot Coena Smith, 69, and Dean Oosthuizen, 25, were minutes into a game capture flight at Tshwarelano Game Lodge in Limpopo on July 30 2019 when the Bell 47-G-3B helicopter they were in began to spin out of control before hitting the ground seconds later.

“According to the passenger, the helicopter was flying at approximately 20 to 30 knots at 200 feet (about 65m) above ground level,” stated the accident report.

“Approximately 15 minutes into the flight, the tail section of the helicopter started vibrating. The pilot disengaged the fuel pump and then engaged it again, but the helicopter continued to vibrate. Approximately five seconds later, the helicopter started spinning to the right (clockwise) with the engine still running.

“The passenger stated the pilot lost control of the helicopter and it continued to spin about six times. The helicopter lost height and impacted the ground, coming to rest in an upright position facing west.”

While the report claimed Oosthuizen managed to free himself from the wreck, he later told You magazine his seat belt snapped on impact and he was thrown through the chopper’s windscreen.

Despite severe back and hand injuries, Oosthuizen managed to free Smith from the helicopter, which had caught fire. Shortly after, Smith complained about pain in his chest and collapsed.

The two men were taken by road to a medical facility in Alldays where Smith succumbed to his injuries.

“I don't know how I’m still alive,” Oosthuizen told the magazine. “If the helicopter had landed a little to the left or right, it would’ve been in long, dry grass and the fire would've spread quickly.”

The helicopter was almost entirely destroyed in the post-impact fire. The tail boom and tail rotor assembly, along with the critical gearbox, survived.

Smith, who had nearly 13,000 hours of flight time, including more than 300 hours on the Bell 47-type, was well-known in game capture circles. Posters on local aviation internet chat forum Avcom paid tribute to Smith’s experience and professionalism, with one noting his game capture facility was in “immaculate condition”.

In the event of a tail rotor failure, the pilot’s only options are to reduce power and carry out an emergency landing procedure called an 'autorotation'.

The Sacaa investigation determined Smith lost control  of the helicopter when the tail rotor failed, “resulting in the helicopter spinning uncontrollably before impacting the ground”.

The helicopter involved in the crash, registration ZS-HGY, was manufactured by Westland Helicopters in 1967. At the time of the crash, the chopper had logged a total of 3,743.9 hours of flight.

The helicopter first appeared on the SA aircraft register in 1978 after being retired from military service. After being issued an airworthiness certificate by the forerunner of the Sacaa, the Bell then operated until April 2012, after which it spent six years out of service, the report said.

In February 2018, the chopper was again issued with a certificate of release to service (CRS) by an aircraft maintenance organisation (AMO), which was valid until February 15 2019. In July 2018, the helicopter was reregistered as a non-type certified aircraft, a common procedure in aviation, especially with older aircraft on which the manufacturer no longer offers technical support.

The Bell’s authority to fly was valid until September 30 2019 or 3,843.9 airframe hours, whichever came first, the report said.

A Bell 47 helicopter similar to the aircraft involved in the accident.
A Bell 47 helicopter similar to the aircraft involved in the accident.
Image: Stefan Krause / Wikimedia Commons

The post-crash investigation discovered that while the tail rotor blades could be turned by hand, when the tail rotor shaft — which is driven by the engine — was turned, the rotor blades did not.

This showed a “discontinuity between the tail drive shaft and the gearbox”, the report said.

On stripping down the tail rotor assembly, investigators discovered that “the pinion gear teeth and bevel gear teeth were worn, resulting in poor contact (operation) during rotation”.

Although the previous two inspections indicated the tail rotor gearbox had been properly checked, the worn gears suggested the gearbox had too little oil and the oil in the housing was old. This might have caused the damage on the gear teeth, which in turn led to the failure of the tail rotor assembly, the investigation found.

The tail rotor counteracts the centrifugal force caused by the main rotor spinning overhead. If the tail rotor fails, the aircraft will begin spinning in the opposite direction of the main rotor and rapidly become uncontrollable.

In the event of a tail rotor failure, the pilot’s only options are to reduce power and carry out an emergency landing procedure called an “autorotation”.

The investigators concluded that the pilot either tried to recover from the spin, but there was not enough height to do so, or that he might have not closed the throttle quickly enough “to conserve power for the flare at the end of autorotation”.

TimesLIVE


subscribe

Would you like to comment on this article or view other readers' comments? Register (it’s quick and free) or sign in now.

Speech Bubbles

Please read our Comment Policy before commenting.