A helicopter crew who were forced to ditch their aircraft off the capital’s coast have been praised for their “prudent” decision.

They landed the AgustaWestland 139 helicopter near Mubarraz Island on April 29 after an alert from the warning system and hearing mechanical noise, said a preliminary report by the General Civil Aviation Authority.

The report said the authority’s review of data from the flight recorder showed the engine oil’s temperature had risen to 119°C, from the normal operating level of about 85°C.

The problem was the failure of an oil-cooling fan, which was an isolated fault, said Leonardo, an Italian aerospace company that produces AgustaWestland aircraft.

Ditching of aircraft occurs about once or twice a year worldwide, when an aircraft’s crew cannot get it to a heliport, oil rig or dry land, said an expert who worked on the investigation.

“These helicopters are operated throughout the GCC in support of the oil and gas industry and are generally reliable, and they operate seven days a week without incident,” said Capt Darren Straker, former head of air accident investigation at the authority and an independent investigator at Straker System Safety.

“Full praise to the pilots for their prudent decision in making the precautionary water landing during the routine flight operated by Abu Dhabi Aviation.”

Capt Straker said the helicopter’s warning system alerted the pilots about the rising engine oil temperature and oil pressure in the main rotor gearbox. The fault was probably caused by a maintenance fault or defective components of the gearbox oil cooling fan assembly, he said.

“This is a serious warning and the emergency checklist advises the pilots to land as soon as possible,” he said.

“Offshore support helicopters are required to have flotation devices attached to the helicopter in case they have to ditch. Normally, the pilots will divert to the closest heliport to avoid damage to the helicopter.”

But the pilots also heard a loud and unfamiliar mechanical noise from the main rotor gearbox.

Previous accidents have been caused by rotor gearbox failures. In Britain in 2009 and Norway in 2006, the rotors of support helicopters separated from the aircraft while in flight.

“This changes the dynamic of the pilots’ concern, as a main rotor gearbox failure is a catastrophic failure,” said Capt Straker.

“The cause of the mechanical noise was not the main rotor gearbox failing. It was related to the internal failure of the main rotor gearbox’s oil cooling fan assembly, which directly leads to the oil temperature increasing and triggers the warning to the pilots.”

Similar incidents in the North Sea in 2012 led to the suspension of helicopter flights.

Last year, an accident which caused a helicopter to be ditched off Lagos in Nigeria forced an entire fleet of helicopters to be grounded.

In Abu Dhabi, the two crew members and passenger of the AgustaWestland 139 helicopter were unscathed. They got into an emergency raft before being rescued by the UAE Coastguard.

The helicopter was in the sea but flotation devices kept it afloat until it was recovered.

There has been several helicopter accidents involving oil rig workers in the UAE. In 2008, seven people were killed in one such accident.

An image of an HNZ AW139 was mistakenly used in this article and has now been removed. This incident is not associated with HNZ helicopters if any way.

Source: www.thenational.ae