Lion Air and Ethiopian Air crashes: an early look at possible mechanical or pilot error

The preliminary investigation of Lion Air flight 610 indicates that prior to the crash a system called Maneuvering Characteristics Augmentation System or MCAS had engaged, possibly without the pilots’ knowledge. The flight pattern of the Ethiopian Air crash is similar to that of the Lion Air crash: both planes crashed minutes after takeoff, during good weather, and with nose-down movements followed by nose-up corrections.

Was the crash a result of problems with the new system? Or did pilot error come into play?

It’s way too early to draw conclusions, but here are a few things to think about…

the purpose of the MCAS

The 737 was designed with larger engines which were also placed higher on the plane, which made it more susceptible to stalling under some conditions (like low speed, like during takeoff).

In order to compensate for this, Boeing added the MCAS which was basically some software that would automatically push the nose down if sensors indicated that the angle –or nose position relative to the ground–was too high.

The MCAS was new to this aircraft yet pilots were not trained on the MCAS and many don’t even know it exists.

why no training on MCAS

Boeing persuaded its customers as well as the Federal Aviation Administration that the new model would handle similar enough to the existing model that 737 pilots would not have to retrain, saving the airlines time and money.

mechanical malfunction

The MCAS engaged during the first several minutes of the Lion Air flight. The Lion Air pilots appeared to have repeatedly tried to compensate for the nose-dive by manually moving the nose up. This pattern continued until the final nose-dive plunged the plane into the sea. The same flight pattern was seen in the Ethiopian Air crash.

possible pilot error

In established emergency procedures, pilots are trained to go through a check list.

The emergency check list states that the sensors for the MCAS should be turned off in the case of a nose-diving problem.

mechanical malfunction

A Lion Air pilot flew the SAME Boeing aircraft just prior to the fatal Lion Air crash. He encountered the same nose-diving.

possible pilot error

This (earlier) Lion Air pilot successfully disengaged the sensors that were sending bad information to the MCAS, according to established emergency protocol, and, in so doing, landed the plane safely. He then left notes in his flight log on the incident. These notes are supposed to be reviewed by the next pilot to fly the plane.

Boeing position

Boeing has maintained that the pilots of the Lion Air flight should have known how to handle the emergency despite not knowing about the MCAS modification.

They have said that various systems on both the MAX and earlier 737s can push the nose down, and that it’s up to the pilots to go through proper protocols when it happens.

Boeing didn’t hide the changes

According to reporting by the NYTimes, Boeing didn’t try to hide the new MCAS from buyers or pilots. The new system was described in maintenance manuals for the plane and was discussed when they met with airlines to talk about the differences between the MAX and earlier versions of the 737.

mechanical malfunction

sensors

In the Lion Air crash, it looks like the MCAS was receiving faulty sensor data about the angle of the plane.

These sensors are located on either side of the fuselage, with the purpose of measuring the angle of the nose. Right now, the theory is that the sensor on the pilot’s side of the plane was sending faulty data.

According to reporting by the NY Times, Boeing’s new 737 simplified the sensor system by only using ONE sensor at a time, while prior designs used sensors on both sides of the fuselage simultaneously. In other words, the new 737 only uses one sensor to collect and send data regarding nose angle to the MCAS, which obviously makes the aircraft more vulnerable.

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