Speaking in London, Steve Dickson, head of the US Federal Aviation Administration (FAA), said he would not clear the Max to resume commercial operations until he has flown the aircraft himself.

Dickson did, however, reveal a “certification flight” could take place in the coming weeks, the BBC reports, as Boeing continues to work on a software update for the 737 Max.

The admission saw Boeing’s stock close 3.6% up on Thursday (6 February) at $342.16.

The 737 Max has been grounded worldwide since March last year following two fatal crashes in just a five-month period.

Lion Air flight 610 crashed shortly after taking off from Jakarta in October 2018, killing all 189 people onboard.

Then in March, Ethiopian Airlines flight 302 came down en route to Nairobi. All 157 people onboard were killed.

Boeing is working on a fix for a flight control system believed to have been active when both aircraft crashed. It is also developing new training and documentation for pilots.

The US manufacturer last month said it didn’t expect the 737 Max to return to service until “mid-2020”; Dickson though said it was "not helpful" to discuss specific timelines for the 737 Max’s return.

Boeing posted a $636 million annual (2019) loss last month, down from a $10.5 billion profit in 2018. It expects the cost of the Max grounding to increase to more than $18 billion.

Norwegian and Tui both have grounded Max aircraft, while Ryanair has been forced to postpone planned capacity growth owing to the ongoing delay in delivery of its new Max fleet.