Boeing 737-Max: Apparently found a cause for the crashes

The co-pilot of the Lion-Air JT 610 flight begged Allah to make a miracle happen in the final seconds before the impact. As the sea surface got closer, he desperately tried to raise the nose of the Boeing 737 Max. The pilot to his left flicked through the manual helplessly. "God is great," these are the last words that were recorded by the voice recorder of the plane that crashed on October 29, 2018 into the sea off the Indonesian capital Jakarta.

What was recorded in the so-called black box was a strange up and down of the machine - and a dramatic increase in speed to over 700 km / h. Exactly here, aviation experts suspect, might explain why the Boeing 737 Max crashed in Indonesia; at the end of a long chain of technical problems, overburdening pilots, and poor manufacturer information.

Accident investigators are currently feverishly looking into the complex accident scene of both the Lion Air aircraft and the Ethiopian Airlines Boeing of the same type that crashed in early March following the scenario that caused the crash. A good 380 Boeing 737 Max are currently on the ground, and unless it's clear what led to the two crashes, they will not lift off again, which represents a financial disaster for the US aircraft manufacturer.

But maybe the experts have taken a step forward, and that could be the high speed that both jets have flown in the last few minutes. The phenomenon is called "blowback" in aviation. It appears at low altitudes, such as those 1500 meters where the Ethiopian Airlines plane was located. There prevails high air pressure, which exerts a fatal effect on the ever faster becoming machine. "The engines for moving the control surfaces do not manage to resist the pressure of the incoming air," explains Björn Fehrm, author of the US aviation website Leeham News.

Stephen Brashear / AFP

The machines of the type had fallen into disrepute after two crashes.

According to Fehrm, the complete scenario that caused the two 737 Max to crash is as follows: The aircraft both had a faulty sensor that measures the angle of attack of the aircraft. The wrong data has led to the onset of a computer system that is supposed to maneuver the plane out of dangerous flight. But instead of saving it, the so-called MCAS ensures that the tail of the horizontal stabilizer steers the aircraft into a dive. This is what both crews, those in Indonesia and those in Ethiopia, have tried to stop by fighting against the false control commands of the air traffic controller and in turn steering the oars in the opposite direction.

The whole acts on the recorded height profiles of the machine like a kind of rodeo, a desperate up and down like a roller coaster ride.

At the same time, the captains speeded up their engines, as this was to prevent the aircraft from stalling. Pilots do this almost instinctively to save themselves from the high-risk flight attitude. Here comes the phenomenon of the blowback (in English "recoil") into play, at least according to Leeham author Fehrm. In the flight data of the Lion Air flight, which have already been published in an interim report of the Aircraft Accident Board of Indonesia, this increase in speed can be seen. The machine accelerated to over 550 km / h, which according to Fehrm "in the zone of the elevator-blowback" comes.

This moment is "deadly"

The air flows at this moment with such force around the control surface at the rear of the machine that the engines can not hold against it to move the rudder against the air masses. The plane has lost the fight against the relentless laws of physics. This moment is "deadly," according to the American expert. In his post, he raises the question of why after the crash of the Lion-Air-Boeing those responsible have given no indication to the pilots of this aircraft pattern, which warns of too high acceleration. So probably the mistake of the Indonesian crew could happen again in a fatal way, just in that crash in Ethiopia.

The cause of the accident is still unclear, and the new explanations are only a theory. But even now, the complexities raise many questions about the responsibility of the Group. Obviously, both crews were completely overwhelmed with the situation. The stress came from the faulty MCAS computer system, whose behavior they could not understand. Their reaction, ie the acceleration of the machine, would therefore be a consequential error, according to Fehrm even the all-important. This would have avenged that the pilots have not received intensive training for the new aircraft types, a selling point of Boeing to the airlines.

Equally irresponsible would have been that the aircraft manufacturer had not even considered it necessary to alert the pilots to the existence of the MCAS, which was necessary because of the particularly large new engines and the changed aerodynamics. In the beginning, and this has already been proven for both crashes, however, was the faulty sensor that has ever triggered the wrong reaction of the flight computer. Here is a decision of the Boeing engineers in the sights of accident investigators and the US judiciary. Thus, the system has no redundancy, that is, it does not use the flight data of the second sensor for its calculations, which also measures the angle of attack of the aircraft.

Between the readings of these two sensors was a 22 degree discrepancy, both in the Lion Air flight and in the Ethiopian Airlines flight. 22 degrees that made the difference between life and death.