Models of a Boeing Co. 737 Max 7 jetliner stand on display at their factory in Sheffield, U.K. (Photographer: Matthew Lloyd/Bloomberg)  

Boeing Close to Issuing Safety Warning on 737 Max

(Bloomberg) -- Boeing Co. is preparing to send a safety warning to operators of its new 737 Max jets in response to the investigation of last week’s fatal crash off the coast of Indonesia that left 189 dead, said a person familiar with the matter.

The bulletin from Boeing will alert airlines that erroneous readings from a flight-monitoring system can cause the planes to abruptly dive, said the person, who asked not to be named discussing details of the manufacturer’s plans. Boeing will warn pilots to follow an existing procedure to handle the problem, the person said.

The warning is based on preliminary findings from the accident involving a Lion Air jetliner, the person said. Under some circumstances, such as when pilots are manually flying, the Max jets will automatically try to push down the nose if they detect that an aerodynamic stall is possible, the person said.

One of the critical ways a plane determines if a stall is imminent is a measurement known as angle of attack, which is a calculation of the angle at which the wind is passing over the wings.

Boeing Close to Issuing Safety Warning on 737 Max

The Lion Air 737 Max 8 dove into the Java Sea on Oct. 29 minutes after takeoff, nosing downward so suddenly that it may have hit speeds of 600 miles an hour before slamming into the water. The pilots radioed a request to return to Jakarta to land, but never turned back toward the airport, according to Indonesia’s National Transportation Safety Committee and flight-track data. The committee said they were dealing with an erroneous airspeed indication.

Indonesia’s transport ministry has scheduled a briefing at 3 p.m. in Jakarta on Wednesday to share updated information on the Lion Air accident.

It wasn’t immediately clear if the airspeed issue had any connection with the angle-of-attack matter. A spokesman for Chicago-based Boeing couldn’t immediately be reached for comment.

In a statement Nov. 5, the Indonesian transportation-safety committee called on the U.S. National Transportation and Safety Board and Boeing “to take necessary steps to prevent similar incidents, especially on the Boeing 737 Max, which number 200 aircraft all over the world.” The committee, charged with finding the cause of the crash, is set to hold a briefing at 4 p.m. in Jakarta.

Boeing Close to Issuing Safety Warning on 737 Max

While additional details of the bulletin aren’t known yet, the warning is the first concrete action to come out of the accident investigation. Boeing has an existing procedure that allows pilots to continue flying in the event that angle of attack readings become erroneous.

Boeing Close to Issuing Safety Warning on 737 Max

The Chicago-based planemaker has delivered 219 Max, the latest and most advanced 737 jets, since the new models made their commercial debut last year with a Lion Air subsidiary. Boeing has more than 4,500 orders for the airliners, which feature larger engines, more aerodynamic wing and an upgraded cockpit with larger glass displays. The single-aisle family is Boeing’s biggest source of profit.

Boeing Close to Issuing Safety Warning on 737 Max

Aircraft and engine manufacturers routinely send bulletins to operators noting safety measures and maintenance actions they should take, most of them relatively routine. But the urgency of a fatal accident can trigger a flurry of such notices.

After an engine on a Southwest Airlines Co. plane fractured earlier this year over Pennsylvania, killing a passenger, CFM International Inc. issued multiple bulletins to operators of its CFM56-7B power plants.

In addition, aviation regulators such as the U.S. Federal Aviation Administration and the European Aviation Safety Agency often follow such actions by mandating that carriers follow the bulletins.

Boeing Close to Issuing Safety Warning on 737 Max

Airlines Await

Lion Air President Director Edward Sirait said the carrier hadn’t yet received any bulletins from Boeing.

“We are still focusing on handling the families of the victims, including returning their remains to their home,” Sirait said by phone. “We will leave the investigation of the accident to KNKT,” he said, referring to the Indonesian transportation safety committee.

Indonesia’s Garuda airlines said it hadn’t received any bulletins from Boeing, either.

“We will tighten up our monitoring and inspections and wait for final report on the investigation,” Garuda Indonesia’s President Director I Gusti Ngurah Askhara Danadiputra wrote in a text message. “So far, there’s no disruption on the operation of our Max jet.”

The nation’s rescue agency, scouring the sea for victims’ remains, said Wednesday that it will extend the search by three more days.

Past Accidents

Pilots raise and lower the nose of Boeing jetliners by pushing and pulling on a yoke in the cockpit, which controls panels at the tail known as elevators. In addition, a system known as elevator trim can be changed to prompt nose-up or nose-down movement.

The angle of attack readings are fed into a computer that in some cases will attempt to push down the nose using the elevator trim system. In the early days of the jet age, the elevator trim system was linked to several accidents. If pilots aren’t careful, they can cause severe nose-down trim settings that make it impossible to level a plane.

Such an issue arose in 2016 at Rostov-on-Don Airport in Russia when a FlyDubai 737-800 nosed over and slammed into the runway at a steep angle, according to an interim report by Russian investigators. That case didn’t involve the angle-of-attack system. One of the pilots had trimmed the plane to push the nose down while trying to climb after aborting a landing, the report said. All 62 people aboard died.

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