Boeing is changing the design of a part around the engine of the 737 MAX and dropping the original supplier, over concern that the part couldn’t be produced at high rates.

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The new Boeing 737 MAX has hit its first development snag, though it won’t affect the planned entry into service in 2017.

Boeing said Tuesday it’s changing the design of a part around the 737 MAX engine and dropping the original supplier, over concern that the part as designed cannot be produced fast enough in the future.

The part is the inner wall of the thrust reverser, a part at the rear of the engine that on landing shifts position to block the jet exhaust and redirect it forward, slowing the airplane.

In the original MAX design, the inner wall is made from a titanium honeycomb, which is more durable and can be made thinner than the carbon-fiber composite honeycomb used on other aircraft such as the 787.

This design was chosen in part to allow the 737 MAX engine pod, which has limited ground clearance because of the new larger engine fan, to be slightly smaller in diameter.

Boeing spokeswoman Lauren Penning said the new design still meets the ground-clearance requirement by substituting thinner insulating panels for the composite blankets used on today’s 737.

“The lines of the airplane do not change … and there is no weight change on the new design,” Penning said.

GKN, the supplier of this new technology, has already produced a number of the titanium parts at its facility in Santa Ana, Calif.

The Wall Street Journal reported Tuesday that the GKN-made titanium parts will be installed on the first 30 or 40 MAXs before the switch to the new supplier. That preserves the schedule for the initial program milestones: rollout of the first one next month, first flight in early 2016 and first delivery the following fall.

However, GKN is having problems manufacturing from this new material at high rates, an issue first reported by The Journal in August.

As a result, Boeing has decided to drop the new material and is negotiating with a new supplier to provide a more conventional version of the part.

“We made this decision to ensure we have a product that is … producible at the high production rates of the 737 program,” Boeing said in a statement.

Boeing has announced that it will ramp up the 737 assembly lines from 42 jets per month now to 47 per month in 2017, to 52 jets per month in 2018, and possibly higher beyond that.

Penning said the performance of the 737 MAX will be unaffected by the switch and that the substituted part will still be more durable and easier to maintain than the same part on the current 737 model.