UPDATE 1-Airbus issues safety advice on Tiger helicopters flying in turbulence

(Adds further information from source)

BERLIN, Sept 6 (Reuters) - Airbus Helicopters has warned pilots of its Tiger military helicopters to be careful of rapid switches from auto pilot to manual mode during turbulence, after initial indications that such a switch may have played a role in a fatal crash in Mali.

The unit of European aerospace giant Airbus said in a statement that the warning was aimed at increasing operators’ safety and should not be seen as an indication of the possible root cause of the crash during a U.N. mission in July, which killed both crew members.

According to a source who has seen the Airbus Helicopters’ bulletin that carried the warning, the bulletin said an unexpected switch from automatic to manual flight mode “may have played a role in the accident, according to information currently available”. The bulletin did not say whether the unexpected switch had happened automatically or been done manually.

German officials last week met to discuss the accident in the Mali desert, but decided to maintain existing flight restrictions on the aircraft after failing to reach a definite conclusion about the cause of the crash.

Airbus said its safety guidance - sent to operators in Germany, Australia, France and Spain - was meant to “standardise all flight manuals and remind operators that crews must adjust their attention to environmental conditions while using the auto pilot during turbulence.”

The guidance reiterated passages already in the flight manuals which instruct pilots not to intentionally enter areas with more than moderate turbulence, and to avoid flying through “areas of severe turbulence.”

A German defence ministry report last month said the Tiger that crashed in Mali had been flying at 250 kilometres (155 miles) per hour at a height of 550 metres (1,800 feet) when it “suddenly sank its nose and entered a sharp dive.” The helicopter crashed 10 seconds later and burst into flames.

The report, however, said it was too early to speculate about the causes of the crash.

German officials continue to investigate the cause of the crash.

Officials say it could take months to complete the probe. At the time of the crash, they said there were no signs the helicopter was downed by an attack.

Germany’s deployment of four Tiger helicopters to Mali earlier this year was controversial since the aircraft required extra maintenance given the strong heat and other environmental conditions in the African country, although officials say the aircraft had been performing normally.

Germany agreed to deploy the Tiger helicopters and four NH-90 transport helicopters after the Dutch military said it could not continue the work in Mali.

But Germany’s increased support was heavily debated in parliament, and required a waiver from the German military allowing the helicopters to operate in higher temperatures.

Germany currently has 26 Tiger helicopters. (Reporting by Sabine Siebold and Andrea Shalal; Writing by Andrea Shalal; Editing by Susan Fenton)