The manufacturer of the helicopter that crashed in Norway last week, killing13 people, says it has sent an advisory to all customers using the Airbus EC-225LP to inspect the suspension bars and fittings of the main rotor, which came loose from the aircraft just before it crashed near a tiny island.

Guillaume Steuer, Airbus Helicopters spokesman, said Wednesday the alert service bulletin, with "mandatory compliance," advises users to send the results of their inspections to the company.

Steuer said the notice was sent late Tuesday to customers using the 176 helicopters currently in service worldwide.

Norwegian investigators said the crash was caused by mechanical failure while flying from an offshore oil rig in the North Sea with 11 Norwegians, one Briton and one Italian on board.