Boeing has said it does not expect its 737 Max plane to return to the skies before the summer, which is longer than initially expected.
The jet has been grounded since March after two fatal crashes, which together killed 346 people.
Boeing has said it is working on a software update intended to fix the problem blamed for the crashes.
But the company has struggled to convince regulators that the planes are safe to fly.
It previously said it expected the planes to be cleared for approval before the end of 2019. But in December, Boeing announced plans to halt production of the aircraft and last week, it confirmed it had found a new problem in the software.
‘Number one priority’
Boeing shares dropped by more than 5% on Tuesday as word of the delay started to spread, prompting the New York Stock Exchange to temporarily halt trading until the company’s formal update.
Boeing said its new guidance was “informed by our experience to date with the certification process”.
“Returning the Max safely to service is our number one priority, and we are confident that will happen.”
The grounding has already cost Boeing more than $ 9bn, and the consequences are starting to spread, with at least one major supplier announcing layoffs. Several airlines dependent on the Max had already said they were not counting on the plane until the summer.
- 29 October 2018: A 737 Max 8 operated by Lion Air crashes after leaving Indonesia, killing all 189 people on board
- 31 January 2019: Boeing reports an order of 5,011 Max planes from 79 customers
- 10 March 2019: A 737 Max 8 operated by Ethiopian Airlines crashes, killing all 157 people on board
- 14 March 2019: Boeing grounds entire 737 Max aircraft fleet
This is the first update on the 737 since new chief executive David Calhoun started last week, and one week before he faces investors when Boeing publishes its quarterly results.
Boeing has been under intense scrutiny since two 737 Max planes crashed within five months of each other, first in Indonesia and then in Ethiopia.
Air safety officials investigating the tragedies have identified an automated control system in the plane, known as MCAS, as a factor in both crashes.
Boeing has said the MCAS software system, which relied on a single sensor, received erroneous data, which led it to override pilot commands and push the aircraft downwards.
It has said it is fixing the software and has overhauled its review procedures.
But US lawmakers, who are investigating the company, have said the firm was aware that the software system could be unreliable. They have accused the company of trying to hide the risks and rush the plane back into service, while criticising the US regulator – the Federal Aviation Administration – for failing in its duty of oversight.
The 737 Max is Boeing’s fastest selling aircraft. An updated version of the company’s short- and medium-haul workhorse, it was designed to be more fuel efficient than its predecessors.