When Boeing pilots were flight testing the new MAX-8 version of the venerable 737 jet they discovered a problem that made the airplane difficult to handle when its speed dropped to a point where it was in danger of triggering an aerodynamic stall, and a loss of control that could lead to a crash.
This is revealed in new reporting by Aviation Week. The report suggests that in order to mitigate the problem Boeing introduced a new system to the flight controls – a system called Maneuvering Characteristics Augmentation System, MCAS, that is at the center of the investigation of the crash of Lion Air Flight 610 that plunged into the Java Sea, killing all 189 people on board.
Pilots flying the more than 200 MAX-8s now in service with airlines across the world have said that they were unaware that the MCAS had been installed and were never instructed in how to use it. That would have included the Lion Air pilots. They were also, therefore, unaware of the reasons why Boeing decided to add the MCAS system.
The problems that were revealed in the test flights arose from the adoption of new engines for the MAX series of the 737. They are larger, heavier and more powerful than on earlier models of the jet.
Fixing these engines to the 737’s wings put Boeing’s engineers up against some unique and challenging problems caused by the age of the jet’s basic design, originating in the mid-1960s.
The 737 sits lower to the ground than other Boeing jets. This is because its designers wanted baggage and cargo to be hand-loaded from the tarmac without mechanical assistance, since the airplane was intended to bring jet service for the first time to many small airports not then equipped for that purpose.
This innovation swiftly became pointless as airports became better equipped and, more vitally, the 737 became the best-selling single-aisle jet in history and Boeing’s most enduring cash cow.
However, the 737’s shorter ground clearance, just 17 inches, became problematic as jet engines grew larger. This could have been countered by a new fuselage and normal length landing gear. But although Boeing introduced new wings, tail surfaces and many other upgrades the fuselage and landing gear remained fundamentally unchanged over decades.
A final crunch moment came with the MAX series. The performance of the 737 was greatly enhanced by the new engines, jointly made by General Electric and the French company Safran, providing a new sweet spot for airlines who wanted the improved economies of a small jet that could fly longer routes, often over oceans.
But those virtues were possible only with an increase in the size of the engines. The size of the MAX engines, specifically the diameter of the huge fan blades at the front, is nearly 70 inches, compared to 61 inches on the older engines, and they weigh 849 pounds more.
In order to attach the new engines and still get a safe distance between them and the ground Boeing lengthened the nose wheel by 9.5 inches and, crucially, had to move the engines, inside their bulging nacelles, further forward from the wing.
It now appears that the changes in the 737’s low-speed handling characteristics resulted from this shift in the weight of the engines, as well as the effects of their increased power.
(In response to questions from The Daily Beast, Boeing declined to confirm the details of the Aviation Week report.)
Normally the onset of an aerodynamic stall is indicated by “stick shake” – the joystick, more accurately the yoke, begins to shake and pilots are trained to instinctively increase speed and push the nose down to recover stability.
As a result of the test flights Boeing seems to have decided that the airplane itself should be able to sense this problem and cure it through its automated flight management system, using MCAS to move the horizontal stabilizer to push down the nose. What they apparently did not anticipate was the possibility that an erroneous message from another system, an angle of attack (the pitch of the wings) sensor, could initiate action by the MCAS, unknown to pilots.
This decision goes to the core of a continuing debate among pilots and safety experts about how far cockpit automation should intervene between pilots and the airplane to detect and correct problems, like this one, that are directly related to retaining control in a potentially dangerous sequence of events.
Many details of a modern jet’s automation systems are buried layers down in architecture that pilots are not required to understand or even know about – unless they turn out to have a potentially dangerous role in some circumstances.
“Loss of control” is now the last remaining consistent cause of crashes. Other once fatal events like flying into unseen terrain or into undetected wind shear on approach to landing have been virtually eliminated by technology that automatically gives the airplane and pilots a new level of situational awareness.
One of several studies directed at loss of control made in the last decade, led by the Federal Aviation Administration, warned that “A high level of competency in hand-flying (both the physical and the cognitive aspects) is necessary for safe flight operations, regardless of the level of autoflight equipment installed…[italics added for emphasis].”
But the challenge to pilots becomes a lot more acute if they are unaware of a critical new system, as in the case of MCAS in the 737 MAX-8.
Aviation Week quotes a pilot who has flown three generations of the 737 who pointed out that a pilot confronted with the “stick shake” alert of an imminent stall could be unaware that the MCAS was activated. He said this was “the most insidious problem” in the new system that “makes the aircraft more difficult to control.”
Boeing president and CEO Dennis Muilenburg has pushed back against the idea that the company had intentionally withheld information about the new system in the MAX-8. In an internal memo directed to employees he said, “You may have seen media reports that we intentionally withheld information about airplane functionality from our customers. That is simply untrue. The relevant function is described in the [operations manual] and we routinely engage customers about how to operate our airplanes safely.”
This seems, at best, disingenuous. The FAA had to issue an emergency directive to airlines to update their flight manuals according to new instructions from Boeing. Muilenburg seems to be alluding to “runaway trim procedures” common to all models of the 737, a series of manual interventions required by the pilot in the event of an upset in the jet’s stability.
Another pilot with a deep knowledge of the 737’s systems told The Daily Beast that Boeing would be looking at whether the Lion Air pilots should have been able to have recovered from the problem by using the runaway trim procedure “in a timely manner.”
But, as the veteran 737 pilot pointed out to Aviation Week, if a pilot is unaware that the problem has been triggered by the MCAS, and was unaware even of that system’s existence, he may not understand the crisis he is confronting in a situation that requires a rapid series of manual actions to correct it.
These are issues that the investigation into the Lion Air crash is attempting to understand in the absence of the one of the most relevant piece of evidence: the cockpit voice recorder. This remains lying at the bottom of the Java Sea (again underlining the aviation industry’s failure to adopt real time streaming of key data to ground bases). Retrieving that data would reveal how the pilots lost control in the final minutes of the short flight on the climb out of Jakarta.
Earlier this week Boeing cancelled a conference call with airlines intended to explain its position on the MAX-8’s flight control systems. It now plans to brief airlines, region by region, next week. More than 90 airlines have ordered the jet, making a total so far of 4,783 due for delivery over the next few years. More than 10,000 737s have been produced since the first flight in 1967.
Its safety record has been outstanding. As each successive model entered service the accident rate has decreased and now stands at 9 fatal accidents for every million flights. The pressure is on Boeing to reassure the airlines – and the public – that the problems with the MAX-8 will not setback that reputation and will be swiftly understood and explained transparently.
“Boeing needs to communicate more and better – not less” Jim Corridore of the aviation research firm CFRA told the Financial Times.
A pilot told the Seattle Times: “I’ve been flying the MAX-8 a couple of times per month for almost a year now, and I’m sitting here thinking, what the hell else don’t I know about this thing?”