The US government has ordered an investigation into the way Boeing’s 737 MAX got its licence to fly.

This comes after the aircraft was involved in two major crashes since October that investigators say share “clear similarities”.

Transport secretary Elaine Chao asked the US inspector general to audit the aircraft’s certification process, according to the BBC.

Chao asked inspector general Calvin Scovel to “assist the Federal Aviation Administration (FAA) in ensuring that its safety procedures are implemented effectively”.

A key focus for investigators so far has been the Max’s anti-stall system, which preliminary investigations suggest may have played a part in the Lion Air tragedy.

Boeing released a statement earlier this week to confirm it is finalising development of a previously-announced software update and pilot training revision for the anti-stall system.

According to Reuters, the US justice department has also begun preliminary inquiries into the FAA’s oversite of the aircraft.

Boeing CEO Dennis Muilenburg has penned a letter to airlines, passengers and the aviation community to express Boeing’s concern for safety and commitment to investigating the two crashes.

“Safety is at the core of who we are at Boeing, and ensuring safe and reliable travel on our airplanes is an enduring value and our absolute commitment to everyone,” he said.

“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.”

The letter was released shortly after Boeing launched their latest aircraft, the Boeing 777X, which the manufacturer has hailed the “largest and most efficient twin-engine jet in the world”.