Australia's safety watchdog has warned that Robinson R44 helicopters that do not receive a fuel tank upgrade will be grounded from 30 April.
"The Civil Aviation Safety Authority [CASA] has issued a direction to all affected R44 helicopter operators about the installation of flexible fuel tanks to reduce the risk of post-accident fires," CASA says in a statement.
"CASA has made it clear that R44 helicopter operators following the Robinson maintenance programme are required to install the new fuel tanks."
CASA says its decision was prompted by the fatal crash of an R44 helicopter in New South Wales on 21 March 2013. Australian media reports say the crash killed the helicopter's four occupants.
CASA notes that Robinson first notified R44 operators of the requirement with a fuel tank service bulletin in December 2010.
In September 2012, Robinson set 30 April 2013 as a deadline for the upgrade. This followed a CASA airworthiness bulletin in June 2012 recommending that the upgrade be undertaken as soon as possible. In February 2013, CASA wrote to R44 operators to emphasise the deadline.