Ruth Fremson/The New York Times

A Boeing 737 MAX 8 plane at the Boeing plant in Renton, Wash., March 20, 2019. After the crash of a Lion Air Boeing 737 Max 8 jet in Indonesia, information largely went unshared as involved parties went into a defensive crouch, a New York Times investigation found.

April 11, 2019

Professor of Aerospace and Mechanical Engineering Shares Insight on the Recent Boeing Plane Crashes

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Over the course of six months the Boeing 737 Max 8 airplane model has been involved in two crashes, killing over 300 people in total. The similarities between the two crashes brought the model into question. Prof. Perrine Pepiot, mechanical and aerospace engineering, weighed in on the mechanics of the crashes based on preliminary data.

The first of the two crashes, Lion Air Flight 610, occurred in Indonesia on October 29, 2018. The latter of the two, Ethiopian Airlines Flight 302, crashed on March 10 en route to Nairobi, Kenya.

“Safety is key for aircrafts, I am not sure if there is any other instance of such a thing to have happened. You can be very unlucky, Malaysian Airlines for example, was very unlucky a few years back,” Pepiot said.

However, unlike crashes in the past, Flights 302 and 610 both demonstrated similarly faulty machinery.

“The two consecutive [Malaysian Airlines] accidents clearly had two different features associated with them. Here [with the Max 8’s] we had the same characteristics, which in aeronautics is extremely worrisome,” Pepiot said.

Boeing has served as a staple in the aerospace industry, holding the distinction of the largest aerospace company as well as the United States’ largest exporting manufacturer. The aerospace titan has ties with Cornell in several facets; most notably through a joint online masters program in Systems Engineering with Cornell’s College of Engineering.

Additionally, the Boeing Company has served as a corporate partner for Cornell Engineering and for the Center for Advanced Human Resources Study. This affiliation has resulted in the matriculation of several notable Cornell alumni to the Boeing Company. Lewis Platt, Mechanical Engineering ‘62, was the chairman of Boeing from 2003 until 2005 and Bill Nye, B.S ‘77, worked as a mechanical engineer developing the 747.

The Boeing 737 is by no means a new plane model: it was first introduced in 1967 and was the company’s introduction into commercial twinjets of this size. Having better fuel economy, quieter engines and more space for passengers, the 737-300 was more economically efficient than its predecessors.

The Max 8, the model involved in both flights 610 and 302, is part of the “Next-Generation 737,” a line of new iterations of the 737 with more efficient engines.

“One way you make an engine more efficient, is by having a larger fan in front of it, so a more efficient engine is larger,” Pepiot said.

To compensate for the enlargement of the engines, the placement of the engines had to be moved further forward and upward.

“On the new version, because the engines are a bit further in front, when you start reaching a high angle of attack, or tilt, the engines are going to be producing a little bit of lift. That will exacerbate the [plane’s] tilting motion,” Pepiot said.

According to Pepiot, while the aircraft is climbing, the placement of the engines tilts the plane further upward at an angle that causes the vessel to stall. To counteract this over-tilting and stalling, Boeing engineers created sensors, known as the Maneuvering Characteristics Augmentation System, to monitor and automatically adjust the plane’s flight angle.

“What the Boeing engineers did was create a software that accounts for this extra [lift] force from the engine and as soon as you were too high in angle of attack an automatic software would bring the [tail of the plane] down to create a force and bring the aircraft back down,” said Pepiot.

However, the MCAS system only requires information from one of these sensors to trigger the response to tilt the plane downward.

“In aeronautics everything is redundant, there are two pilots, anytime there [are] sensors, there are in fact at least two of them installed. But with two sensors providing conflicting information, it can be difficult to resolve which one was giving the right information,” said Pepiot.

In the recent crashes, it is hypothesized that one of the sensors provided incorrect information regarding the positioning of the plane. The sensor wrongly indicated that the plane was tilted too far upward and triggered a response to tilt the nose of the plane downard.

However, since the plane was not actually tilted upward in the first place, the sensor caused the plane to overshoot the downward adjustment, and subsequently plummet in altitude. Early data displays fluctuations in the altitude of the plane, which indicates that the pilots of both flights attempted to rectify the positioning of the plane, only to be overridden by the automated system.

The two crashes have raised questions regarding the regulation of Boeing and the 737, especially under the realization that many pilots were not aware of the M.C.A.S. system’s implementation until the first of the two crashes.

Without any prior knowledge of the system it would be difficult for pilots to overcome a malfunction. It has come to light that Boeing engineers, as opposed to Federal Aviation Administration officials, were vetting the 737 Max 8 for flight.

Questions remain with regard to the future of Boeing, with the grounding of 737 Max 8’s around the globe, and ongoing investigations into the relationship between Boeing and the FAA.