Haryo Satmiko, second from right, deputy head of Indonesia's National Transportation Safety Commission, delivers a preliminary report on Lion Air Flight 610 during a news conference Wednesday in Jakarta. (Bay Ismoyo/AFP/Getty Images)

Boeing’s latest airliners lack a common override feature that, in some dangerous circumstances, allows pilots to reliably pull planes out of nosedives and avert crashes such as last month’s fatal plunge by Lion Air Flight 610, aeronautics experts and pilot groups say.

The state-of-the-art 737 MAX 8 airplanes do not have this feature, yet the company failed to prominently warn pilots of the change even as airlines worldwide began taking delivery of the new jets last year, pilots say.

“We were completely in the dark,” said Dennis Tajer, a 737 pilot and spokesman for the Allied Pilots Association, representing American Airlines pilots.

Questions surrounding the crash have turned a harsh spotlight on Boeing’s latest update to its workhorse 737 line, the world’s most popular commercial airliner. Boeing’s stock is down nearly 12 percent since the Oct. 29 crash, even after a slight uptick on Wednesday amid a broad market upswing.

Revelations about the doomed Lion Air flight, released Wednesday in a preliminary report by Indonesian investigators, also exacerbated long-standing debates over what degree of automation is safest for airplanes — and how human pilots should be able to take full control.

“Automation is there to make us safer and more productive in the cockpit,” said Jon Weaks, president of the Southwest Airlines Pilots Association, a union representing pilots at Southwest Airlines. “But that never replaces the overriding commandment that the pilot has to fly the airplane and know what the aircraft is doing.”

Boeing said in a statement Wednesday that it had addressed the “flight control functionality” of its updated automated system with more than 60 airlines worldwide and at regional conferences since 2016.

“We are confident in the safety of the 737 MAX,” the company said. “Safety remains our top priority and is a core value for everyone at Boeing. We are taking every measure to fully understand all aspects of this accident, working closely with the investigating team and all regulatory authorities involved. While we can’t discuss specifics of an ongoing investigation, we have provided two updates for our operators around the world that re-emphasize existing procedures for these situations.”

The Boeing 737 aircraft first flew in 1967 and — with several iterations and upgrades — quickly became the mainstay of international short-haul aviation. The 737 MAX is the fastest-selling plane in Boeing history, with almost 4,700 planes sold or on order, and it is flown by nearly 40 airlines worldwide.

Boeing issued a bulletin on Nov. 6 that described how 737 MAX pilots should override the automated system suspected of causing the Lion Air crash.

The investigative report, which stops short of determining the cause of the crash, chronicles the chaotic moments aboard Flight 610 before it hit the waters off the coast of Java last month, killing all 189 passengers and crew on board.

That end came after a battle between its flight crew and a computerized control system that repeatedly tilted the plane downward because of a malfunctioning sensor, according to the report.

Correcting the path of the plane would have required a multistep process, something that pilots and other aeronautics experts said may have been difficult to remember and execute during a life-threatening emergency.

Members of the Lion Air flight crew repeatedly attempted to manually arrest the plane’s dive, but the system reasserted itself each time. The crew lost control of the jet, which struck the water at 450 miles per hour, the report found.

“What they were focused on was keeping the airplane in the air,” said Clint R. Balog, a pilot and aeronautics expert at Embry-Riddle Aeronautical University. “That’s always your first priority. You troubleshoot problems only after you’ve got the aircraft safe.”

Previous iterations of 737s would have switched off key automatic control features when the pilot first pulled back the control column, a standard manual override feature in generations of airplanes. Investigators found that the final yank on the control column of Flight 610 registered almost 100 pounds of pressure, suggesting desperation in the cockpit as the plane plummeted.

Pilots expressed concern about the changing nature of the controls and Boeing’s delayed disclosure of the change. The company sent out its public alert more than a week after the Lion Air crash. Tajer and others said they were aware of no earlier notice of the change in how 737 MAX planes operate compared with their predecessors.

Aeronautics consultant Douglas M. Moss, a retired United Airlines pilot, said that Boeing and government regulators, among others, share blame for allowing the delivery of planes that operated in unexpected ways during emergencies and for failing to make the changes clear to pilots charged with flying them safely.

“All those systems failed the crew and passengers,” said Moss, of AeroPacific Consulting. For pilots of a diving plane, he added, “the initial instinctive reaction is to pull back the control column, and in this case, that’s not going to work for very long.”

Moss said that aircraft makers seek market advantage by convincing buyers that new generations of planes can be easily flown by existing pilots, without expensive new training. The computer system that failed, called the Maneuvering Characteristics Augmentation System, or MCAS, sought to make the 737 MAX operate as similarly as possible to the older 737s, despite having larger engines placed farther forward on the wings. 

The investigation found that, for days before the crash, the 737 MAX had experienced trouble with a sensor that measures the plane’s “angle of attack” — essentially whether it is dipping down, tipping up or level. The malfunctioning sensor is key to correct operation of the MCAS, which is charged with detecting and correcting dangerous stalls. 

The report suggests the MCAS acted as though the plane was stalling because it was receiving incorrect information from the faulty sensor. Every time the flight crew pulled the nose back to level, within seconds, the MCAS tipped it back downward.

The Federal Aviation Administration reiterated the caution in Boeing’s bulletin.

“What we do as a matter of practice when any manufacturer puts out a bulletin such as this, we put out what’s called an Airworthiness Directive,” said Gregory Martin, of the FAA, “which gives those instructions and procedures the full weight of the legal authority of the FAA to ensure that those bulletins are performed.”

The pilots’ concerns echoed a broader debate over how commercial jets can be automated safely. Manufacturers including Airbus and Boeing have been integrating computerized processes into commercial piloting procedures since the 1980s. The Airbus A320 sparked controversy after it was introduced in 1988 because it was among the first planes to have its flight functions directed via computer as opposed to stick and rudder controls.

In 1988, an Airbus A320 crashed at a French air show, killing a woman and two children. That accident was ultimately attributed to pilot error, but the pilot reportedly blamed factors including incorrect altitude information fed through the plane’s computers. 

In the decades since, computerized processes have been integrated into nearly every industry. Experts say automation has made airlines safer.

“Automation isn’t the debate,” said Richard Aboulafia, an analyst with Teal Group aerospace consultancy. “It’s about the ease of manual override and the extent to which that is included in training and communications.”