MOSES LAKE — The fleet of four Mitsubishi Regional Jets (MRJ) currently undergoing flight testing here were grounded following an engine problem last week that forced a plane into an unscheduled landing in Portland.

“Safety is our first priority,” Mitsubishi spokesperson Morgan Heysse told the Columbia Basin Herald. “Per our operation manuals and the safety protocols of our flight test program, we will resume flights once the cause has been identified.”

According to Heysse, the left engine on MRJ No. 2 shut down unexpectedly and without being told to during flight testing near Portland. The aircraft landed safely at Portland International Airport.

A problem was discovered in the engine, a Pratt & Whitney PW1200G. According to Heysse, the malfunctioning engine was replaced, and the plane flown back to Moses Lake.

“The damaged engine has been transported to a (Pratt & Whitney) facility for a more thorough investigation,” she said.

Matthew Bates, a spokesman for Pratt & Whitney, said the company was working with Mitsubishi to assess the problem “and any further implications to the flight test program.”

According to a report from the Aviation Analysis blog, this is the second failure for Pratt & Whitney’s latest generation of geared turbofan engines, which includes the PW1200G. The first failure, in 2014, involved a related engine on a Bombardier CS-100, a small jetliner designed to carry 100-130 passengers — slightly larger than the MRJ.

The engines include a complex gear mechanism designed to make them more fuel-efficient.

Mitsubishi Aircraft established a flight test center in Moses Lake about two years ago, and has been testing four aircraft — including a model set to be delivered to All-Nippon Airways — intensively since they began arriving late last year.

The largest customer for the MRJ is Utah-based regional carrier SkyWest, which has ordered 100 of the larger MRJ90 models, with an option for 100 more. SkyWest operates as contract regional carrier serving over 230 cities for Alaska Airlines, United Airlines, American Airlines, and Delta.

Charles H. Featherstone can be reached via email at [email protected].