South Korea has grounded its fleet of Korea Aerospace Industries (KAI) KUH-1 Surion utility helicopters, pending the replacement of gearboxes.

According to a report by state news agency Yonhap, quoting an official at Seoul’s Defence Acquisition Program Administration, Airbus Helicopters informed it that the fatal crash of an H225 in Norway was due to a “defective main gearbox”. The report adds that 57% of the Surions in military service will need their gearboxes replaced, and that Airbus will reimburse the South Korean government.

KAI confirms that it is working with Airbus Helicopters to “retrofit the defective Surions”. The rotorcraft, which resembles the AS332 Super Puma, was developed indigenously in South Korea, with extensive assistance from the European company.

Responding to the report, Airbus Helicopters states: “As the supplier of the Surion main gearbox, which bears close similarities with the AS332 L2 and EC225 LP main gearboxes, Airbus Helicopters has issued an emergency alert service bulletin calling for the withdrawal of a specific type of second-stage planet gears in order to provide increased reliability and safety across the Surion fleet.

"We are providing our full support to Korea Aerospace Industries and Korean operators as they manage the associated retrofit programme,” it adds.

Flight Fleets Analyzer shows that there are 52 Surions in service, with another 49 on firm order.

KAI Surion

Korea Aerospace Industries

The South Korean army operates 45 examples, with orders for 47 more, KAI has four, and the Korea National Policy Agency has three, with a firm order for another. In addition, the South Korean Forestry Aviation office has a single Surion on order.

There are also 204 letters of intent, from the army (153), the South Korean marines (40) and the police (11).

On 30 June, Norwegian investigators reiterated their belief that metal fatigue in a gearbox component was behind the fatal crash of an H225 near Bergen in late April. The SHT agency also warns that mechanisms installed in the Super Puma to provide advance warning of a gearbox failure may be inadequate.

The rotorcraft (LN-OJF) came down after the main rotor assembly broke away from the fuselage at around 2,000ft . All 13 people on board were killed.