Boeing found itself in hot water following two fatal passenger airplane crashes of its 737 MAX aircraft in just six months.

Boeing CEO Dennis Muilenburg sought to reassure airlines in a letter last month, saying “safety is at the core of who we are.”

“We know lives depend on the work we do, and our teams embrace that responsibility with a deep sense of commitment every day. Our purpose at Boeing is to bring family, friends and loved ones together with our commercial airplanes — safely,” said Muilenburg.

The Boeing CEO also said the company will release a software update and further train pilots for flying the 737 MAX, addressing concerns related to the recent Lion Air crash.

“The tragic losses of Ethiopian Airlines Flight 302 and Lion Air Flight 610 affect us all, uniting people and nations in shared grief for all those in mourning,” he added. “Our hearts are heavy, and we continue to extend our deepest sympathies to the loved ones of the passengers and crew on board.”

The United States and several other countries grounded the plane after last month’s Ethiopian Airlines crash.

“Based on facts from the Lion Air Flight 610 accident and emerging data as it becomes available from the Ethiopian Airlines Flight 302 accident, we’re taking actions to fully ensure the safety of the 737 MAX. We also understand and regret the challenges for our customers and the flying public caused by the fleet’s grounding,” added Muilenburg.

“Work is progressing thoroughly and rapidly to learn more about the Ethiopian Airlines accident and understand the information from the airplane’s cockpit voice and flight data recorders. Our team is on-site with investigators to support the investigation and provide technical expertise.

The Ethiopia Accident Investigation Bureau will determine when and how it’s appropriate to release additional details.”