Boeing has issued a safety bulletin to all airlines that operate the Boeing 737 Max aircraft, and the Federal Aviation Administration is expected to follow with an Airworthiness Directive mandating safety protocols for U.S. carriers.
The moves by Boeing and the FAA follow the Oct. 29 crash of a 2-month-old Lion Air Boeing 737 Max jet that killed all 189 onboard when the plane plunged into the sea shortly after taking off from Jakarta, Indonesia.
Safety regulators of other nations typically follow directives issued by the FAA.
The focus in the crash investigation appears to have turned to the flight data sensor and the possibility it returned erroneous readings.
Two U.S. airlines fly the Boeing 737 Max 8. Southwest has 26 while American Airlines has 16. Combined, the airlines have hundreds more on order.
United Airlines flies another variant, the 737 Max 9, which also is covered by Boeing’s bulletin. None of those U.S. airlines have reported the issue covered by Boeing’s bulletin regarding its 737 Max aircraft.
Bloomberg News was the first to report that the FAA planned to issue an airworthiness directive for the 737 Max. Bloomberg wrote that “under some circumstances, such as when pilots are flying manually, the Max jets will automatically try to push down the nose if they detect that an aerodynamic stall is possible.”
It’s the sensor readings that are thought to incorrectly show that such a stall is possible.
A Boeing statement said that its safety bulletin, sent to airlines on Tuesday, directs flight crews to “existing flight crew procedure” on how they should respond to erroneous data for the sensor which monitors an aircraft’s “angle of attack,” a vital measurement in determining lift after takeoff.
Aerospace industry expert Jon Ostrower writes via his blog The Air Current that “the erroneous (angle of attack) input can pitch the aircraft’s stabilizer trim down for up to 10 seconds at a time.”
Boeing’s bulletin is said to include instructions to pilots on how to compensate for automated controls that may be triggered by incorrect sensor readings.
After Boeing’s update, the FAA followed on Wednesday with a statement that, according to Bloomberg, it plans to issue an airworthiness directive on the issue and “will take further appropriate actions depending on the results of the investigation.”
The Wall Street Journal, also citing unnamed “people familiar with the matter,” writes “the moves are the first public indication that investigators suspect a possible software glitch or misinterpretation by pilots – related to an essential system that measures how high or low a plane’s nose is pointed – may have played an important part in the sequence of events that caused the Boeing 737 Max 8 to plunge into the Java Sea.”
“Boeing and the FAA are providing operators with information and a reminder of how to address a stabilizer trim nose down condition,” says John Cox, aviation expert and USA TODAY’s Ask the Captain author. “There are several steps a crew can take, but in the end they switch the electric stabilizer trim off and revert to manual trim.”
“Stabilizer trim” refers to flight controls addressing the pitch of the airplane, according to Cox.
It wasn’t immediately clear if Boeing planned an further update to its Tuesday bulletin, but comments made to The Associated Press indicated they expected one.
For now, that leaves airlines to ensure that they’re following the latest updates.
Boeing has delivered more than 200 models of the aircraft and has received orders for more than 4,500 of its 737 Max models.
For now, though, industry analysts played down the possible impact on U.S. airlines and travelers.
“No impact at all so far,” Richard Aboulafia, a vice president at Teal Group who analyzes commercial aviation, told USA TODAY. “There’s a working hypothesis, and a caution to watch crew procedure in the event that this problem repeats. If the hypothesis is correct, there could, conceivably, be minor equipment modifications and a renewed emphasis on crew procedure.”
He added, “there is nothing, so far, that indicates a serious problem for airlines and nothing that would impact the safest form of transportation ever created.”
Another industry Henry Harteveldt, co-founder of the Atmosphere Research Group travel consultancy, echoed those sentiments.
He said it’s too early make conclusions until the FAA actually issues its directive on the subject.
He points out the agency regularly issues directives. While some are for serious items, many address relatively minor issues.
“Right now, based on what information is available, it appears this will be a fairly unobtrusive type of directive in terms of affecting airline operations,” Harteveldt said. “I’m not expecting aircraft to be grounded. I’m not expecting airlines to take the airplanes out of service.”
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