Outboard Engines Swapped By Outsourced Maintenance Facility

Heads are likely rolling at Japan Airlines and Singapore's ST Aviation Services after the airline discovered one of its 747s has been flying for seven months with the left outboard and right outboard engines mistakenly swapped.

Airline officials admitted the error Wednesday, stating it occurred when ST Aviation Services performed an overhaul on the aircraft in February. The plane began flying passenger routes with the mis-attached engines in April.

The swap of the aircraft's two outboard engines never compromised the safety of the aircraft, said JAL authorities to Kyoto News.

While its true the engines operated just as they would normally under regular thrust conditions, the engines are not interchangeable with each other: the engines' thrust reversers were incorrectly positioned in the swap.

During reverse thrust braking procedures, each engine directed the thrust towards the fuselage of the aircraft, instead of away from it as intended -- causing little issue with braking performance, although it possibly added to the noise level in the cabin.

Also as a result of the mistake, components in one of the engines were not inspected at the scheduled 650 flight-hour interval -- instead flying over 850 hours before the switch was discovered during a November maintenance check.

According to Kyoto News, Japan's Land, Infrastructure and Transport Ministry directed the airline "to take measures to prevent any recurrence" of the engine swapping error. For its part, JAL will revise its in-house procedures to ensure that inspections on the planes are conducted after outsourced maintenance work.

The airline's current policy only calls for checking documents after the completion of maintenance work.

FMI: www.jal.com