The ban came after satellite trajectories showed pilots attempting to arrest the descent of the bucking airliner that was similar to an October Lion Air 737 MAX-8 disaster in Jakarta, Indonesia, officials said. The combined death toll from the two accidents included 346 passengers and crew.
Acting FAA Administrator Daniel K. Elwell told CNBC that the aviation agency was “working tirelessly” since the most recent accident to determine a cause. New information the agency received March 13 “verified for us” that the Ethiopian Airlines flight track “was close enough to the track of the Lion Air flight” that crashed in October “to warrant the grounding of the airplanes so that we could get more information from the black boxes and determine if there is a link between the two, and if there is, to find a fix to that link.”
The “space-based ADS-B” satellite data the agency initially received was “very raw and very hard to interpret,” Elwell noted. Most general aviation pilots are familiar with Automatic Dependent Surveillance-Broadcast technology, which determines an aircraft’s position from celestial-derived data and delivers it to the cockpit and air traffic controllers.
“There was not an obvious link … initially,” he added, until “the company that has that data, Aireon, the NTSB, and Boeing, were able to do some enhancements to that track return” that triggered similarities the agency could not discount. “The full track of the Ethiopian flight was very close to Lion Air.” Evidence discovered on the ground at the Ethiopian crash site “was very similar” to the Indonesian crash.
Elwell reiterated to CNBC that the emergency order to ground the aircraft was authority vested in the FAA “with me. I did make the decision” to take the fleet out of service after consulting “all counsel and expertise” available to the FAA. He said he also discussed it with Transportation Secretary Elaine Chao and President Donald Trump, who agreed with the decision.
The Seattle-based commercial aircraft manufacturer faced growing criticism surrounding the implementation of its Maneuvering Characteristics Augmentation System (MCAS), proper documentation, and pilot training.
The technology was designed to automatically control and stabilize the large aircraft, particularly upon takeoff and climb when pilots could experience an upward pitching moment from the airliner’s larger and more energy-efficient jet engines, pilots familiar with the system said.
An airline pilot with 737 MAX-8 flying experience who wished to remain anonymous explained to AOPA that the new augmentation system affected the stabilizer trim but noted several ways to defeat it. “It doesn’t move any primary controls,” and MCAS doesn’t function when the autopilot is active. “When the autopilot is on, it isn’t even a player,” the pilot added. Switching off the electric trim overrides the system and cut-off switches are located on the center pedestal “near the red fire cutoffs between the pilot and first officer and both of them” can access the switches. The pilot also noted MCAS doesn’t work if flaps are extended in the aircraft’s normal takeoff configuration.
A system malfunction “should appear to a pilot the same way a runaway trim wheel appears,” the pilot continued. “The result is that we have a runaway trim checklist—and a procedure” to work around it. You turn off the electric trim and go to a manual reversion. It’s something we train for. It is true that Boeing didn’t tell anyone about it [MCAS]—so that is problematic.”
He noted that the control yokes on models with the new technology have a lighter feel than on previous 737 models and can be touchy at high angles of attack. “The idea of the new system is, if it trims a little down, you’ll pull the same [force] as in the old airplanes.” In previous versions of the 737, “When you pull five pounds of force on the yoke, you get five degrees of pitch change, and when you pull 10 pounds, you get 10 degrees” of pitch change.
However, “On the MAX, it only takes about a 10-pound pull to get 15 degrees of pitch” because the aircraft responds quicker to input. “The trim system dials in about 2.5 degrees of nose-down trim in a little less than 10 seconds,” he added. “On the ground it feels different on the nose and the sight picture is a little different” from previous 737 models. “It’s [enough to be] noticeable,” the pilot said.
In the air, the 737 MAX “flew just like a Boeing. I like to hand-fly it myself and they did a pretty good job of the control input and on response. It didn’t feel much different” than other 737s.
“When Boeing built the MAX, in order to increase fuel efficiency, they went with a different engine, explained Fred Tecce, a commercial aviation expert. “Because the 737 sits pretty low on its landing gear, [Boeing] had to move the engines up a little bit and move them forward a little bit” on the MAX versions. “In order to compensate, they extended the nose gear by eight to 12 inches" and repositioned the engines which "affected the airplane’s pitch characteristics and center of gravity.”
Tecce concurred that control inputs and the resulting pitch changes were challenges that had to be overcome in the latest version of the world’s best-selling aircraft.
“In order to compensate for what the engineers perceived to be an issue with respect to pitch, they added this MCAS system that operates when the autopilot is off and the angle of attack exceeds certain limitations and when the airplane is banked pretty steeply.” He said the technology runs the stabilizer pitch down for several seconds and it “reassesses and will start again until it believes the airplane has reached a safe angle of attack, and it operates without the pilots knowing [about it].”
Tecce noted that in the case of the Lion Air Boeing 737 MAX crash, “now the airplane is pitching down and actually moving the control wheel will not stop that system. If the pilot uses the trim system on the yoke, the [MCAS] system will stop" but "if the airplane isn’t in the proper attitude it will reactivate,” Tecce said, further forcing the aircraft downward if pilots fail to recognize the situation and take proper corrective action.
A pilot familiar with the system pointed out that recognizing this scenario was crucial to determine if there was a problem that warranted activating the trim cutoff switches. Additionally, if the autopilot is engaged, activating a yoke trim switch disconnects the autopilot and gives full control back to the pilot immediately.
Tecce did not fault the FAA for taking a wait-and-see approach. “A lot of people throwing a lot of rocks at the FAA. Since 2010 we’ve had one aviation fatality” in the United States. “Our safety record is astonishing,” he said. “I don’t think there’s anything wrong with the airplane. If you talk to the pilots who fly them, they’ll tell you it’s not the airplane so much as whether or not the manual properly describes what’s going on.”