March 12, 2019

On March 10, an Ethiopian Airlines (ET) Boeing 737 MAX 8 operating Flight ET-302 from Addis Ababa, Ethiopia (ADD) to Nairobi, Kenya (NBO) crashed shortly after takeoff, killing all 157 people onboard. The crash is the second, high-casualty incident in six months involving a 737 MAX 8 aircraft, following the October 2018 crash of Lion Air (JT) Flight JT-610 in Indonesia, and has led numerous countries and airlines to ground 737 MAX fleets due to safety concerns.

WorldAware recommends travelers strongly consider avoiding travel on the 737 MAX 8 and the larger 737 MAX 9 until more information is available regarding the cause of Flight ET-302's crash. Some small pieces of information available regarding Flight ET-302's crash parallel the Flight JT-610 crash, which authorities have linked to an issue with the 737 MAX's flight control system. Until authorities can rule out the possibility that the same issue contributed to Flight ET-302's crash, further groundings of the 737 MAX remain possible, including a potential worldwide grounding. Authorities will likely be able to prove or disprove the link between the flight control system issues and the crash of Flight ET-302 within the next two weeks; if they disprove the link, all existing groundings will likely be lifted.

Key Judgments

  • WorldAware recommends travelers strongly consider avoiding travel on 737 MAX aircraft until authorities determine whether a known issue with the aircraft's control systems played a role in Flight ET-302's crash.
  • Within the next two weeks, authorities are likely either to lift all existing groundings of the 737 MAX or ground all 737 MAX aircraft worldwide.
  • A worldwide grounding of the 737 MAX would not cause significant disruptions to global air travel, as the type only accounts for a small portion of the global 737 fleet.
  • Ethiopian Airlines has a reputation for strong operational and safety standards, and remains listed as Preferred in WorldAware's Worldcue Airline Monitor.


The Crash

Little information is available regarding the cause of Flight ET-302's crash. Although authorities have recovered the aircraft's cockpit voice recorder and flight data recorder, also known as the "black boxes," investigators have not issued any preliminary findings. According to the airline, the aircraft did not have any known maintenance issues before it took off, but the pilot reported a problem with the plane shortly after takeoff and asked permission to return to ADD. The airline did not specify the problem that the pilot reported.

Images from the crash site are consistent with an aircraft hitting the ground at high speed and in a steep dive, as the aircraft left an impact crater and was destroyed in the accident. News reports and images indicate debris from the crash was contained in a relatively small area, suggesting that the aircraft did not break up in flight. Some eyewitnesses indicated the aircraft was trailing smoke and trying to turn immediately before it crashed; however, eyewitness reports of plane crashes are frequently inaccurate and should not be taken as conclusive in the absence of corroborating evidence.

Data from flight-tracking website Flightradar24 indicates that the aircraft's vertical speed - the rate at which it was climbing or descending - was unstable throughout the flight, suggesting the aircraft alternated between climbing and descending. Flightradar24's coverage in the area of the crash is poor, however, and it remains unclear if the data is accurate.


737 MAX Groundings

Boeing 737 MAX 8 aircraft are being grounded worldwide due to safety concerns. Photo: Wikimedia Commons

As of March 12, authorities in numerous countries and the EU have ordered airlines in their territories to ground their 737 MAX fleets. Some countries have also banned the aircraft from their airspace. Most 737 MAX operators in other countries have also chosen to ground their 737 MAX fleets. As of the afternoon of March 12, the US, Canada, and Panama are the only remaining countries where airlines are continuing to operate the 737 MAX in significant numbers; it is unclear if regulators in these countries will ground the aircraft as well. All groundings so far have been precautionary and unrelated to specific findings from the crash of Flight ET-302.

The groundings of the 737 MAX only impact a small portion of the global 737 fleet. Of more than 7,000 Boeing 737s in service worldwide, only approximately 350 are 737 MAX aircraft. Some of the groundings have only affected the 737 MAX 8, the variant involved in both the Flight JT-610 and Flight ET-302 crashes, while others have also affected the larger 737 MAX 9 variant, which has the same flight control system that is causing concern on the 737 MAX 8. The 737 MAX 8 and MAX 9 should not be confused with the 737-800, -900, or -900ER variants, which are far more common and do not share the part of the 737 MAX flight control system that is causing the concerns. As such, these variants are not affected by any of the 737 MAX groundings.

A worldwide grounding of the 737 MAX fleet would not cause significant disruptions to global airline travel. The 737 MAX makes up only a small portion of the fleets of most airlines that operate the aircraft, and most airlines that operate it have other aircraft that can serve their 737 MAX routes. While sporadic flight cancellations or reschedulings would be likely, they would probably only last a few days until airlines can either fill the routes with their spare aircraft or lease aircraft to cover the gaps in their schedules. A few airlines operate 737 MAX aircraft on routes that none of their other aircraft can feasibly operate; airlines may have to suspend these routes unless they can lease suitable alternatives. The most notable examples of such flights are several of Norwegian Air International's (D8) transatlantic flights; Norwegian grounded the 737 MAX on March 12.

The status of the global 737 MAX fleet will likely be determined within the next two weeks. Airlines and regulators are closely monitoring the investigation into the crash of Flight ET-302 for evidence that it was linked to an aspect of the 737 MAX's flight control system, known as the Maneuvering Characteristics Augmentation System (MCAS). The MCAS played a role in the crash of Flight JT-610 in October 2018, but almost all pilots, airlines, and regulators had agreed that changes in pilot training and procedures had resolved the safety concerns posed by the system. MCAS issues are clearly discerned from an aircraft's flight data recorder (FDR), and authorities have recovered the FDR from Flight ET-302, so authorities should have firm evidence within two weeks on whether the MCAS played a role in Flight ET-302's crash.

Safety Concerns with the MCAS

The Boeing 737 MAX family of aircraft is the newest generation of Boeing's popular 737 model, having entered service in 2017. Like all modern airliners, the 737 MAX is subject to strict certification requirements and underwent rigorous testing before entering service, but questions about the aircraft's safety have risen since the crash of Flight JT-610 in October 2018.

While outwardly similar to the older 737 models it replaced, the 737 MAX had several crucial differences, including relatively poor handling in high angle of attack (AOA) situations - situations in which the aircraft's nose points steeply upward but the plane does not climb. These handling issues made the aircraft vulnerable to an aerodynamic stall, an issue that can cause a crash. To address the issue, Boeing added the MCAS to the 737 MAX's flight controls, which uses the aircraft's trim system to automatically push the aircraft's nose down if the AOA becomes too high.

The crash of Flight JT-610 showed that a single faulty AOA sensor can cause the MCAS to activate repeatedly when the aircraft is in level flight. If the pilots do not react, this activation pushes the aircraft into a nosedive. According to Boeing, pilots can counteract the MCAS by pulling the aircraft's nose back up and resetting the aircraft's trim, but the MCAS will reactivate five seconds later. Pilots can ultimately stop the MCAS from activating by pressing the automatic trim cutout switches, which disables the entire automatic trim system. The pilots of Flight JT-610 did not press these switches, possibly because their training course for the 737 MAX did not mention the MCAS; the MCAS ultimately activated approximately 30 times on the flight before the aircraft crashed.

Although some of the limited information available regarding Flight ET-302's crash bears striking parallels to the Flight JT-610 crash, there is currently no conclusive evidence that the flight experienced an MCAS issue. The pilot's reports of aircraft problems shortly after takeoff, the unstable vertical speed, and the final steep dive were all features of both crashes. However, other issues could account for this sequence of events, so the parallels are not proof that both aircraft encountered the same issues. Other pieces of evidence from Flight ET-302's crash, including the eyewitness reports of smoke coming from the aircraft and the unstable vertical speed immediately from takeoff are not consistent with an MCAS issue; the MCAS only activates when the aircraft flaps have been retracted, so it would not affect an aircraft immediately after takeoff when flaps are deployed.

Following the crash of Flight JT-610, there was significant controversy over two aspects of the MCAS. Some experts criticized the MCAS design for taking data from only one AOA sensor, meaning that a single failure can cause an erroneous and potentially dangerous MCAS activation. Indonesian authorities, US pilots' unions, numerous industry experts, and some former Boeing employees all criticized Boeing for allegedly not providing adequate documentation of the MCAS in 737 MAX manuals and training materials. Numerous 737 MAX pilots said they were unaware of the system before Boeing outlined it in a technical bulletin after the crash.

Boeing, airline authorities, and regulators have since addressed the documentation and pilot training issue. Boeing has provided specific guidance to pilots on how to deactivate the MCAS. The procedures are relatively straightforward, and 737 MAX pilots have expressed confidence they would be able to quickly and effectively deal with any future erroneous MCAS activations. The presumed effectiveness of these procedures was a major factor behind airlines and regulators retaining confidence in the 737 MAX following the crash of Flight JT-610. Boeing is also working on an update to the 737 MAX flight control systems that would reduce the likelihood of an erroneous MCAS activation.

Should evidence from the crash of Flight ET-302 indicate that the MCAS played a role, it would disprove beliefs that the MCAS issue had been adequately addressed and likely lead regulators to ground the 737 MAX worldwide until Boeing developed a permanent fix for the issue. Such a grounding would likely last for several months while Boeing developed, tested, and certified a permanent fix.

Conversely, if data from Flight ET-302's FDR shows that the MCAS did not play a role in the recent crash, all existing groundings of the 737 MAX will likely be lifted within a day. The MCAS is the main cause of airlines' and regulators' concerns over the 737 MAX, and proof that it did not contribute to the Flight ET-302 crash would strengthen airlines' and regulators' belief that improved training has adequately addressed the MCAS issue.

Ethiopian Airlines

Ethiopian Airlines is listed as "Preferred" in WorldAware's Worldcue Airline Monitor, and WorldAware does not have any current plans to downgrade the carrier. Ethiopian Airlines has a good safety record and has earned a reputation for strong operational and safety standards. The airline is certified under the International Air Transport Association's (IATA) IATA Operational Safety Audit (IOSA) program, the most comprehensive global airline audit program, and holds certifications from both EU and US authorities for flights to their respective territories. The airline is also a member of Star Alliance, one of the world's three major airline alliances, and has numerous codeshare agreements with major international carriers, indicating these operators' confidence in Ethiopian Airlines' operational and safety standards, by allowing their customers to fly on the carriers' flights.

WorldAware will be monitoring the investigation into Flight ET-302's crash closely for any indications of shortcomings in Ethiopian's operational and safety standards. WorldAware cannot rule out the possibility of downgrading the airline to "Not Preferred" status in the future. The airline's current "Preferred" status is not considered marginal, however, so any downgrade would require clear evidence of significant problems with the airline's operational and safety standards.


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