SEATTLE (Reuters) - Boeing Co’s top executive told employees on Monday he was confident in the safety of the U.S. manufacturer’s fastest-selling 737 MAX aircraft in the wake of two deadly crashes since October.

FILE PHOTO: Dennis Muilenburg, CEO, Boeing speaks during a roundtable discussion on defense issues with U.S. President Donald Trump at Luke Air Force Base, Arizona, U.S., October 19, 2018. REUTERS/Jonathan Ernst/File Photo

An Ethiopian Airlines passenger jet bound for Nairobi crashed minutes after take-off on Sunday, killing all 157 people on board and raising questions about the safety of the Boeing 737 MAX 8 model. The same type flown by Lion Air crashed off the coast of Indonesia in October, killing all 189 on board.

“We are confident in the safety of the 737 MAX and in the work of the men and women who design and build it,” Boeing Chief Executive Officer Dennis Muilenburg told employees in an email seen by Reuters. “Since its certification and entry into service, the MAX family has completed hundreds of thousands of flights safely.”

Muilenburg said Sunday’s crash was “especially challenging” coming only months after the loss of Lion Air Flight 610.

Boeing rolled out the fuel-efficient MAX 8 in 2017 as an update to the already redesigned 50-year-old 737. That family of single-aisle aircraft is the cash cow of the world’s largest planemaker, competing against European rival Airbus SE’s A320neo family.

Boeing has delivered more than 370 MAX Airplanes to 47 customers, Muilenburg said.

In the wake of Sunday’s crash, China ordered its airlines to ground the jet, a move followed by Indonesia and Ethiopia. Other airlines, from North America to the Middle East, kept flying the 737 MAX 8 on Monday after Boeing said it was safe.

Southwest Airlines Co, which operates the largest fleet of 737 MAX 8s, said it remained confident in the safety of all its Boeing planes even as it received a rush of queries from customers wanting to know if they were booked to fly on a 737 MAX 8.

There are still unanswered questions about the causes of the Lion Air crash, and officials and safety experts said it was too soon to draw links with the Ethiopian incident.

Muilenburg said Boeing was fully supporting the crash investigation and providing technical assistance under the direction of the U.S. National Transportation Safety Board and Ethiopian authorities.

Muilenburg also said Boeing was “further strengthening” support to the 737 team, manufacturing operations and customer service. He urged employees to “stay centered on the facts and avoid speculation” while the investigation unfolds.

“Speculating about the cause of the accident or discussing it without all the necessary facts is not appropriate and could compromise the integrity of the investigation,” Muilenburg said.