Boeing’s boss has refused to admit that a system introduced in its 737 Max 8 aircraft was flawed following two fatal plane crashes.
Appearing in front of investors and the media, Dennis Muilenburg maintained the system was only one factor in a chain of events that led to the disasters.
But new reports have raised fresh questions about the plane’s safety.
It has emerged that whistleblowers connected to Boeing contacted the US airline regulator about the system.
Meanwhile, the Wall Street Journal revealed that Boeing failed to activate a safety feature linked to sensors on 737 Max planes bought by its biggest customer, Southwest Airlines.
The 737 Max is grounded worldwide after an Ethiopian Airlines flight crashed near Addis Ababa in March, killing all 157 people on board.
It follows a crash by Lion Air in Indonesia five months earlier, which claimed 189 lives.
‘Chain of events’
Facing shareholders and the press for the first time since the Ethiopian Airlines tragedy, Mr Muilenburg said that both accidents occurred because of faulty data from a sensor which triggered the plane’s Manoeuvring Characteristics Augmentation System (MCAS).
The system, which is designed to stop the plane from tipping higher and stalling by forcing the nose lower, was a new addition to the 737 Max when the aircraft was launched in 2017.
Mr Muilenburg said that the MCAS system met its “design and certification criteria” and pointed to a number of other scenarios that may have contributed to the fatal accidents including actions taken or not taken by pilots.
He added: “As in most accidents, there are a chain of events that occur. It is not correct to attribute that to any single item.”
A preliminary report into the Ethiopian Airlines flight found that the plane nosedived several times before hitting the ground.
In the case of the Lion Air flight, a report suggested that the system malfunctioned, and forced the plane’s nose down more than 20 times before it plummeted into the sea.
Boeing has developed and is testing a software update for MCAS.
Mr Muilenburg appeared amid reports that a number of whistleblowers had contacted the Federal Aviation Administration (FAA) after the Ethiopian Airlines crash, regarding issues related to the sensors and MCAS system.
It also emerged that Boeing did not activate a “disagree alert” feature on the 737 Max 8 that warned pilots if the sensor was transmitting faulty data about position of the plane’s nose.
The Wall Street Journal reports that Southwest was not aware of the “angle of attack” sensor feature until after the Lion Air crash and that the warning was available only if a company bought an additional safety feature.
Mr Muilenburg claimed early on Monday: “We don’t make safety features optional.”
In a later statement, Boeing then said: “The disagree alert was intended to be a standard, stand-alone feature on Max airplanes. However, the disagree alert was not operable on all airplanes because the feature was not activated as intended.
“The disagree alert was tied or linked into the angle of attack indicator, which is an optional feature on the Max. Unless an airline opted for the angle of attack indicator, the disagree alert was not operable.”
It said that once the 737 Max 8 returns to the skies, it will “have an activated and operable disagree alert and an optional angle of attack indicator”.
Boeing has already seen a $1bn (£773m) drop in revenues related to the 737 Max crisis and some customers have reviewed their orders.
On Tuesday, Virgin Australia said it had reached an agreement with Boeing to defer deliveries of 737 Max aircraft.
In a statement, the company said it would delay first deliveries of Boeing Max 737 jets from November 2019 to July 2021.
“We will not introduce any new aircraft to the fleet unless we are completely satisfied with its safety,” Virgin Australia Chief Executive Paul Scurrah said.