The US Federal Aviation Administration has identified a new risk that Boeing Co must address on its 737 MAX before the grounded jet can return to service, the agency said on Wednesday.
The risk was discovered during a simulator test last week and it is not yet clear if the issue can be addressed with a software upgrade or will require a more complex hardware fix, sources with knowledge of the matter told Reuters.
The FAA did not elaborate on the latest setback for Boeing, which has been working to get its best-selling airplane back in the air following a worldwide grounding in March in the wake of two deadly crashes within five months.
The new issue means Boeing will not conduct a certification test flight until July 8 in a best-case scenario, the sources said, but one source cautioned it could face further delays beyond that. The FAA will spend at least two to three weeks reviewing the results before deciding whether to return the plane to service, the people said.
Last month, FAA representatives told members of the aviation industry that approval of the 737 MAX jets could happen as early as late June.
The world's largest planemaker has been working on the upgrade for a stall-prevention system known as MCAS since a Lion Air crash in Indonesia in October, when pilots were believed to have lost a tug of war with software that repeatedly pushed the nose down.
A second deadly crash in March in Ethiopia also involved MCAS. The two accidents killed a total of 346 people.
"On the most recent issue, the FAA's process is designed to discover and highlight potential risks. The FAA recently found a potential risk that Boeing must mitigate," the FAA said in the statement emailed to Reuters. "The FAA will lift the aircraft’s prohibition order when we deem it is safe to do so."
Boeing said in a securities filing late on Wednesday that the FAA has asked it to address through software changes a specific flight condition not covered in the company's already-unveiled software changes.
The US planemaker also said it agreed with the FAA's decision and request, and was working on a fix to address the problem.
"Boeing will not offer the 737 MAX for certification by the FAA until we have satisfied all requirements for certification of the MAX and its safe return to service," Boeing wrote in the filing.
Boeing's aircraft are being subjected to intense scrutiny and testing designed to catch flaws even after a years-long certification process.
Two people briefed on the matter told Reuters that an FAA test pilot during a simulator test last week was running scenarios seeking to intentionally activate the MCAS stall-prevention system. During one activation it took an extended period to recover the stabilizer trim system that is used to control the aircraft, the people said.
It was not clear if the situation that resulted in an uncommanded dive can be addressed with a software update or if it is a microprocessor issue that will require a hardware replacement.
In a separate statement, Boeing said addressing the new problem would remove a potential source of uncommanded movement by the plane's stabilizer.
A hardware fix could add new delays to the plane's return to service.
The FAA also said on Wednesday that it continues "to evaluate Boeing's software modification to the MCAS and we are still developing necessary training requirements. We also are responding to recommendations received from the Technical Advisory Board. The TAB is an independent review panel we have asked to review our work regarding 737 Max return to service."
American Airlines Group Inc and Southwest Airlines Co earlier canceled flights through early September as a result of the grounding. On Wednesday, United Airlines said it also was removing MAX flights from its schedule through Sept. 3.
737 Max accidents
On October 29, 2018, Indonesian Lion Air Flight 610 from Soekarno–Hatta International Airport in Jakarta to Depati Amir Airport in Pangkal Pinang, crashed into the Java Sea 12 minutes after takeoff. All 189 passengers and crew were killed in the accident. The preliminary report tentatively attributed the accident to the erroneous angle of attack data and automatic nose-down trim commanded by MCAS. The 737 MAX aircraft was delivered 2 months and 16 days prior, on August 13, 2018.
Later on March 10, 2019, Ethiopian Airlines Flight 302 from Addis Ababa in Ethiopia to Jomo Kenyatta International Airport in Nairobi, Kenya, crashed six minutes after takeoff near Bishoftu, killing all 157 passengers and crew aboard the aircraft. This plane was delivered 3 months and 23 days prior, on November 15, 2018, two weeks after the Lion Air accident.
Initial reports indicated that the pilots struggled to control the airplanes. Experts suggested evidence pointed to MCAS as at fault in the crashes. After the crash of flight ET302, Ethiopian Airlines spokesman Biniyam Demssie said in an interview that the procedures for disabling the MCAS were just previously incorporated into pilot training.
Signs of MCAS activation in both accidents came from satellite data, as each aircraft experienced extreme fluctuations in vertical speed, and witnesses saw the Ethiopian flight crash at an extreme nose-down angle. Pilots in both aircraft reported flight control problems and requested permission to return to the airport.
What is Mcas?
Maneuvering Characteristics Augmentation System (MCAS) is a computerized function of the aircraft flight control system and is referred to as a "flight control law" in avionics terminology. The placement of the 737 MAX's larger CFM LEAP engines gave the airplane a tendency to pitch up under certain conditions, and the MCAS was intended to mitigate those effects to make the 737 MAX handle like its immediate predecessor, the 737 Next Generation, "particularly at slow speeds and high angles of attack". .
The MCAS is vulnerable to a single point of failure, contrary to established design principles requiring redundancy for safety critical systems. In reading a single angle of attack sensor, the system has no safeguards against erroneous information that can activate MCAS and trigger other cockpit warnings.
Boeing finally publicly acknowledges MCAS problem
All Boeing 737 Max planes were grounded in March. On April 4, 2019 Boeing publicly acknowledged that MCAS played a role in both accidents and described a software update that would prevent the possibility of unintended MCAS activation. Boeing also said it would upgrade the cockpit display to give pilots a better indication of MCAS status and would improve pilot training materials.
Technical specs of 737 Max