Last week's Lion Air crash in Indonesia has invited Boeing to issue a security warning to all 737 MAX airlines,…
Last week’s Lion Air crash in Indonesia has invited Boeing to issue a security warning to all 737 MAX airlines, instruct pilots on what to do if a specific sensor error occurs.
Following the lethal crash of a Lion Air jet in Indonesia last week, Boeing prepared Tuesday night to warn all airlines operating its new 737 MAX of the possibility of an instrument failure that could lead to the plane entering a dangerous dive, according to a person who is informed about the details of the bulletin.  The security alert comes in what is called a service bulletin that is issued to all airplane operators and contains instructions on exactly what pilots should do if the permit occurs.
It is normal for the Federal Aviation Administration to follow such a warning with an “Airworthiness Directive” which makes it mandatory, and this is expected in the next few days.
Investigators look at the cause of the Lion Air crash, which killed all 189 passengers and crew, has identified a potential failure of a sensor telling the pilot and the airplane computer the “attack angle” of the aircraft, which is the angle between the wing and the flow  A plane will have a high angle of attack when climbing. Too high angle would cause a boat.
The concern caused by the flight pattern and the first survey of the Indonesian crash is that the sensor may possibly supply incorrect information about this angle to the airplane, which in turn triggers other errors.
Especially with the sensor that falsely indicates that the nose is too high, if it does not, it causes an automated system response that “trims” the horizontal tail of the plane to begin to lay the nose on the planet.
At the same time, it causes a minimum speed indicator to tell the pilot that the plane is near a stall, which also causes the pilot’s control column to shake as a warning. And the air velocity indicators on both sides of the airplane are disagreeable.
Pilots can use extra force to fix the nose, but the error repeats so that the nose pressure starts again 10 seconds after correction.
“If the nose is trimmed on an airplane, it will be difficult for the crew to keep it,” said the person informed of Boeing’s bulletin. “The nose goes down and they have to fight it. It takes a lot to keep it from diving. Especially if you have a crew that’s confused and do not know what’s going on.”
This description fits exactly the fly pattern of the Lion Air- the jelly that crashed.
For 12 minutes before it crashed the heights up and down as if the pilots fought to maintain the height, move the plane up and then swing down again repeatedly.
Pilots are usually trained on how to handle a runaway trim situation, said the person informed about Boeing bulletin, but it is with everything that works as it should. In this case, the control column, the shake alert and the disagreement of the aviation indicator combine all to create confusion and keep the pilots very busy.
Boeing instructs pilots in the bulletin that if this failure occurs, “initially, higher control forces may be needed to overcome the nasal wear stabilizer’s trim.” The instructions continue to say that after initial stabilization, the automatic trim system on the horizontal tail should be turned off and trimmed performed manually.
Pilots can turn off the auto trim system with a shut-off switch driven by the thumb on the control column.
“Everything comes from the Indonesian crash,” said the person who was informed of the Boeing bulletin. “I’m not aware of any other operator who has this problem.”
More than 200 MAX are in service around the world. Boeing is building 737 in Renton, and expects that 40 to 45 percent of those built this year are MAXs, the rest being the previous model.
The news of the service bulletin was reported on Tuesday evening by Bloomberg News. A Boeing spokesman refused to comment.