A scale model of Boeing’s 737 Max aircraft.
Photo: Stephen Brashear (AP)

Aerospace giant Boeing is preparing to alert pilots of its new 737 Max line of passenger jets warning that inaccurate readings in an onboard flight-monitoring system can cause the planes “to abruptly dive,” Bloomberg reported on Tuesday, citing a source with knowledge of the matter.

According to Bloomberg, the safety warning is linked to the crash of a Lion Air aircraft last week off the coast of Indonesia, killing an estimated 189 people. The news agency wrote that “existing procedure” can be used to compensate for the issue, which appears to be the result of a serious problem with systems designed to prevent the jets from stalling at dangerously high speeds:

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.

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The news agency noted that angle-of-attack errors can cause pilots to lose control of an aircraft and make it impossible to correct the course of a flight, and this was particularly an issue when jet aircraft were first entering circulation. However, it’s unclear whether the warning is being issued because investigators have conclusively determined that a flight-monitoring system error was the cause of the crash. Such warnings are commonplace after a serious aviation accident, given how grave those disasters tend to be.

However, Bloomberg wrote that the pilots in the Lion Air crash reported an “erroneous airspeed indication” after taking off from Jakarta airport and before they slammed into the water at around 600 miles per hour, according to Indonesia’s National Transportation Safety Committee.

According to the Insurance Journal, the U.S. Federal Aviation Administration has yet to require 737 Max jets undergo inspections, and the issue hasn’t been reported domestically:

“Any action that the FAA would take regarding that incident would have to wait until we have findings,” agency acting Administrator Daniel Elwell said Monday after a speaking engagement in Washington.

Investigators haven’t disclosed any reports of other airspeed failures on 737 Max aircraft. The FAA, which regulates the U.S. aviation industry, hasn’t received any reports of airspeed issues occurring on the model in the U.S., said a person familiar with the agency’s reviews. The person asked not to be named because he wasn’t authorized to speak about the issue.

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Over 200 737 Max jets are already in use in commercial aviation, Bloomberg added, though Boeing has orders for 4,500 more.

[Bloomberg]