AgustaWestland AW139 crash near Arabian Gulf, 8nm off Mubarraz Island, Abu Dhabi, United Arab Emirates

The AW139 had flown from Abu Dhabi to the Dhabi II rig with two crew and five passengers, four of whom disembarked, then continued towards the Bunduq installation. A minute into the climb, at about 490 feet, the crew received a high main rotor gearbox oil temperature warning reading 109°C. The commander levelled off and descended to 500 feet to reduce load per the quick reference handbook, and they diverted for Mubarras Island 18nm away. As the temperature continued rising he descended to 200 feet in preparation for ditching. Passing 210 feet at 119°C, the crew heard a loud grinding noise from the gearbox and the commander ditched. The flotation system was activated before touchdown and kept the aircraft afloat while all occupants evacuated to the life raft, from where the coast guard rescued them; the left aft float then slowly deflated and the helicopter capsized. Investigators found the deflation was caused by a tear in the bag fabric and seam delamination, and that in-flight activation of the floats was not compliant with the system's certification, causing the deployed float cover to fragment — the remains probably tearing the bag. Many flotation bags were found to fail inflation tests at shop visits because of seam problems. The gearbox oil temperature had risen because the oil cooling fan failed through bearing damage, stopping airflow through the cooler. The manufacturer subsequently issued instructions and additional maintenance tasks for early detection of cooling fan failures.