The Boeing engineer who has played a key role in the company’s response to the grounding of the 737 Max is retiring. Boeing said Wednesday that John Hamilton planned to retire last year as chief engineer of commercial airplanes, but he stayed on to help get the Max back into service.

Hamilton appeared before Congress in October alongside CEO Dennis Muilenburg to defend and explain the design and production of the Max, which has been grounded since March following two deadly crashes.

Hamilton has spent 35 years at Boeing and served as chief project engineer for several planes including the 737 NG, the version that preceded the Max. He will be replaced by Lynne Hopper, vice-president of engineering for Boeing’s commercial airplanes business.