Boeing Commercial Airplanes Chief Engineer John Hamilton who led the response to the 737 Max crisis earlier this year, is retiring. Hamilton, along with Boeing CEO Dennis Muilenberg had testified before the House Transportation and Infrastructure Committee in October.

The retirement was revealed in an internal memo circulated by Boeing Commercial Airlines CEO and Boeing Chief Engineer Greg Hyslop.

“John had planned to retire last year, but we asked him to stay on to help us with the 737 Max investigations and return to service efforts ... We are immensely grateful to John for lending his expertise and leadership during a very challenging time,” the memo, which was accessed by CNBC Wednesday stated.

Lynne Hopper, Vice-President, Engineering for Commercial Airplanes, will take over from him. Hamilton retired after working for 35 years at Boeing.

The 737 Max is the fastest commercial airplane produced by Boeing and remains under scrutiny for flaws in its MCAS software, which is alleged to have produced cheaply, endangering safety.

The Boeing 737 Max design, avionics, and marketing are under scrutiny since two crashes in October 2018 and March 2018 causing deaths of 346 people in total.

Clients such as India’s SpiceJet, who have placed orders for the plane are now developing their own training programs and certifications, along with independent certifications. Many aviation authorities including the U.S. Federal Aviation Administration (FAA) are holding clearance for the jets to fly again.

The FAA is planning to review each 737 Max individually before clearing it, which is expected to further delay the certification of the airliners, which have been grounded since March. Boeing executives, though, have stated repeatedly, that they hope that FAA will sign off on clearance this quarter.

Carriers such as United Airlines, JetBlue and American Airlines have placed orders with competitor Airbus for long-range single-aisle planes during the same duration.