Virgin Australia has pushed back delivery of the first of its troubled Boeing 737 MAX 8 aircraft to 2025.

The move comes after safety concerns following two disastrous aircraft crashes.

The airline has also converted 15 of its MAX 8 aircraft on order to MAX 10s, with the first deliveries delayed from November this year to July 2021.

Virgin said the restructure would result in a significant deferral of capital expenditure and provided access to the “superior economic benefits” of the MAX 10.

“I’m pleased that we have reached an agreement with Boeing to convert a further 15 of our Boeing 737 MAX 8 aircraft to MAX 10s and defer deliver of our order to July 2021,” Virgin Australia group chief executive Paul Scurrah said in a statement to the ASX on Tuesday.

“Safety is always the number one priority for Virgin Australia. As we have previously stated, we will not introduce any new aircraft to the fleet unless we are completely satisfied with its safety. We are confident in Boeing’s commitment to returning the 737 MAX to service safely and as a long-term partner of Boeing, we will be working with them through this process.

“The revised timing also results in a number of positive commercial benefits for the Group. This includes a significant deferral of capital expenditure by extending the use of existing aircraft given the relatively young age of our fleet along with providing the Group earlier access to the superior operational economics of the MAX 10 aircraft.”

It came after the CEO of Boeing defended the company’s safety record and declined to take any more than partial blame for two deadly crashes of its best-selling plane even while saying Monday that the company has nearly finished an update that “will make the airplane even safer.”

Chairman and CEO Dennis Muilenburg took reporters’ questions for the first time since accidents involving the Boeing 737 MAX in Indonesia and Ethiopia killed 346 people and plunged Boeing into its deepest crisis in years.

Mr Muilenburg said that Boeing followed the same design and certification process it has always used to build safe planes, and he denied that the MAX was rushed to market.

“As in most accidents, there are a chain of events that occurred,” he said, referring to the Lion Air crash on October 29 and the March 10 crash of an Ethiopian Airlines MAX.

“It’s not correct to attribute that to any single item.”

The news conference, held after Boeing’s annual meeting in Chicago, came as new questions have arisen around the MAX, which has been grounded worldwide since mid-March.

Southwest Airlines said over the weekend that Boeing did not disclose that a safety feature on the 737 — an indicator to warn pilots about the kind of sensor failure that has been linked to both accidents — was turned off on the MAX.

Southwest said it found out only after the first crash of the Lion Air MAX. Published reports said that federal regulators and congressional investigators are examining safety allegations relating to the MAX that were raised by about a dozen purported whistleblowers.

And the pilots’ union at American Airlines said Boeing’s proposal for additional pilot training on the MAX doesn’t go far enough. For instance, the union for American Airlines pilots wants, at a minimum, mandatory additional training to include video demonstrations of how to respond to failures of systems on the plane.

The annual meeting came six months to the day since the Lion Air crash. Mr Muilenburg told shareholders that Boeing is close to completing an upgrade to flight software on the MAX “that will ensure accidents like these never happen again.”

In the brief news conference that followed, Mr Muilenburg said — as he has several times before — that the accidents resulted from a “chain of events” that included the erroneous activation of flight software known as MCAS.

Mr Muilenburg pointed to actions by the pilots on the two flights, who he said did not “completely” follow the standard procedure when uncommanded tail movements begin to push the jet’s nose down.

Boeing has conceded that in both accidents, MCAS was triggered by faulty readings from a single sensor and pushed the planes’ noses down.

“We know this is a link in both accidents that we can break. That’s a software update that we know how to do … this will make the airplane even safer,” Mr Muilenburg said.

Mr Muilenburg took six questions from reporters, including whether he will resign — he has no intention of doing that — and left as reporters persisted, including one who pointed to the deaths of 346 people and urged the CEO to take more questions.

Besides the software update, Boeing will present the Federal Aviation Administration with a plan for training pilots on changes to MCAS. The company is pushing for training that can be done on tablet computers and, if airlines want to offer it, additional time in flight simulators when pilots are due for periodic retraining.

A requirement for training in simulators would further delay the return of the MAX because of relatively small number of flight simulators. The union for American Airlines pilots wants mandatory additional training on checklists for responding to certain emergencies.

“Not every pilot that goes out there and flies is a Boeing test pilot,” said Dennis Tajer, a 737 pilot and spokesman for the pilots’ union at American. “The responsibility to train those men and women doesn’t rest just with the airlines, it rests with Boeing and the FAA too. If something happens anywhere in the world, it affects all of us.”

During the one-hour annual meeting, shareholders elected all 13 company-backed board nominees, including newcomer Nikki Haley, the former South Carolina governor who lobbied for a Boeing plant there, and former U.S. ambassador to the United Nations.

Several shareholder resolutions were defeated, including one to name an independent chairman whenever possible instead of letting the CEO hold both jobs.

A chairman-CEO “is not always a bad thing, but at times of crisis it’s hardly ever a good idea,” said Matt Brubaker, CEO of business-strategy consultant FMG Leading, who was not involved in the debate. “The place they are in now, they need the scrutiny of an inwardly focused CEO to drive change.”