Boeing 737 MAX still faces questions over MCAS flight control update before flying again**

Boeing 737 MAX
The Boeing 737 MAX has sensors on either side of its fusilage to detect Angle of Attack. With the latest flight control software updates to MCAS, both sensors will need to agree on a reading to activate MCAS, which can only be activated once and won't override a pilot's ability to control the plane using the control column. (Boeing)

The Federal Aviation Administration on Wednesday rescinded its order grounding the troubled Boeing 737 MAX, but some pilots and engineers remain unconvinced that airlines can safely fly those planes.

A major concern remains over Boeing’s update in recent months to its flight control software known as MCAS and its ability to prevent future MAX crashes.

In late 2018 and early 2019, two MAX planes crashed, killing 346 passengers and crew aboard Lion Air Flight 610 and Ethiopian Airlines Flight 302. The plane was grounded afterwards.

MCAS (Maneuvering Characteristics Augmentation System) was cited early on by Indonesian investigators for relying on just one Angle of Attack (AOA) sensor on the Lion Air MAX plane, which had a fault,  instead of both of sensors on either side of the fuselage.

 As a result, Lion Air pilots were unable to determine their true airspeed and altitude and every time pilots tried to pull up from a dive, MCAS pushed the nose down, eventually resulting in a fatal crash.  A similar situation occurred in the Ethiopian Airlines crash because a single AOA sensor continued to incorrectly reported a high AOS, causing MCAS to activate, Boeing said later.

Boeing’s updates to MCAS now compare measurements from two AOA sensors and MCAS will only be activated if both sensors agree.  Additionally, MCAS will only be activated one time and the software will never override a pilot’s ability to control the plane using the control column alone.

The FAA was careful to say that its Nov. 18  decision  doesn’t allow the MAX to return immediately to the skies. The agency must still approve pilot training and related changes for each U.S. airline. American Airlines is the first airline planning to use the plane daily on flights from Miami to New York from Dec. 29 through Jan. 4 as part of a phased approach to return the MAX to service.

Software concerns remain

Veteran pilot and career software engineer Gregory Travis told Fierce Electronics that Boeing has not fixed structural design problems with the MAX aircraft and is instead relying on updated MCAS software to provide critically needed safety for pilots.   

“Given how badly [Boeing] screwed up the original MCAS implementation, there is no confidence that a significantly more complicated implementation, created by the same people responsible for the first, will do anything other than add additional failure nodes,” Travis said via email.

“For well over a year now, Boeing has fought tooth and nail to keep MCAS on the 737 MAX as opposed to deleting it and seeking a waiver…or developing aerodynamic modifications to the airframe to make MCAS unnecessary,” he added.

“Instead, Boeing has spent billions of dollars trying to make MCAS viable,” he added. “What that tells me is there is a serious aerodynamic/handling problem that presents itself if MCAS is not operational. Otherwise, they would have gone the faster and cheaper route of getting rid of it altogether.”

Ultimately, Travis worries if MCAS becomes inoperable in a future flight, that a flight crew could face an emergency.

Boeing's response

**A Boeing spokesman said in response to Travis that his basic assertion is inaccurate and that MCAS is not required for aerodynamic stability, a view held by Patrick Ky, executive director of the the European EASA regulatory safety body, in a recent public slide presentation that says the 737 MAX "is stable even without MCAS."

**The Boeing spokesman added on Sunday, "In fact, MCAS is not designed to operate during normal flight conditions at all; rather, it works to improve pilot handling qualities only when the plane encounters unusually high angles of attack." 

**Also, the Boeing spokesman pointed to the FAA's Airworthiness Directive on page 10 that adds, "The MCAS on the 737 MAX improves the pilot handling qualities (maneuvering characteristics) during non-normal flight conditions, specifically when the airplane is at high AOAs." 

**On the Boeing website, an FAQ notes that MCAS only activates when three conditions happen at the same time during a flight:  the AOA reaches a high value due to very slow speeds or aggressive maneuvering; the pilot is flying manually and the airplane flaps are up.

**Travis said Boeing's explanation was "b.s." adding, "If MCAS was only for handling and not to cure some fundamental problem, then Boeing would not have wasted 18 months and billions of shareholdr money trying to fix it.  They would have simply deleted it and made pilots and airlines aware that a high angles of attack, the 737 MAX behaves differently that early generation 737s."

**He added that Boeing and the FAA need to supply test data to verify their claims rather than relying on the EASA to do so.

Concerns over FAA disclosures

Travis has been outspoken about MCAS and is one of 11 pilots and engineers concerned with how the FAA has reviewed the MCAS updates and other actions related to ungrounding the MAX.  That group includes Chesley “Sully” Sullenberger, known for his successful landing of an airliner in the Hudson River and Sara Nelson, president of the largest flight attendant union, Association of Flight Attendants.

All 11 in the group support a freedom of information request before a federal court filed by, a non-profit public interest group, seeking disclosure of FAA documents pertaining to the ungrounding of the MAX.

 The case is before Judge Colleen Kollar-Kotelly in the U.S. District Court for the District of Columbia.

“Clearly, Boeing doesn’t want to make any changes to the plane and its hardware, and that’s the fundamental problem,” said Paul Hudson, president of FlyersRights, in a telephone interview.  “The MAX is aerodynamically unstable and you keep it in the air with software, basically.”

If there is a malfunction in MCAS, it will disconnect and “the pilots will be on their own to operate it manually,” Hudson added. “Because the FAA has not released data on how pilots can operate MAX without MCAS and autopilot, it makes the plane safety, in our view, very problematic.”

Because not all testing protocols and test results have not been made public, there is no way to know if the MAX can fly, for instrance, over an ocean under manual pilot operation for five hours if an engine went out or faced another problem, Hudson said.  Hudson said he has met with top FAA officials for reassurances but has not obtained answers.

FAA fights full public disclosure

The FAA in the federal case (19-cv-03749) argued in a Nov. 18 filing that certain information must be kept from the public, citing confidential Boeing trade secrets. “Disclosure of Boeing’s confidential commercial information would lead to foreseeable harm to Boeing’s commercial interests and would interfere with the FAA’s ability to obtain necessary safety information,” the FAA argued in the filing. 

Hudson said he expects a full hearing on the information request before the judge by the end of the year. and other groups could also appeal the FAA ungrounding order separately as well, but Hudson would not comment on whether such an appeal will take place.

Specifically, the full FAA ungrounding order of 115 pages says tests have been conducted of MCAS and that MCAS passed the tests “but the FAA doesn’t say what the test were and what the results were,” Hudson said. “There’s no way outsiders like Travis can review whether the MCAS fix is going to work safely.”

Hudson said it is “real stretch” for the FAA to keep trade secrets and MCAS test protocols and results secret. In a prior case that brought against the FAA in 2017 over airplane seat sizes, a judge ruled that FAA could not use secret data to reach its rulings.

Pilots union backs ungrounding

Whether and others prevail in their safety concerns with MAX could be a long shot.  In addition to airlines that are depending on the MAX to provide greater fuel efficiency and other modern benefits, the huge Air Line Pilots Association International has supported the FAA ungrounding decision. 

“ALPA believes the engineering fixes to the flight-critical aircraft systems are sound and will be an effective component that leads to the safe return to service of the 737 MAX,” ALPA said in a statement on Nov. 18.  ALPA represents 59,000 pilots at 35 U.S. and Canadian airlines.

**This story was updated on Sunday, Nov. 22, with the comments from a Boeing spokesman in response to the original story and Travis' reaction to the Boeing comments.