While the Federal Aviation Administration (FAA) has formally un-grounded the Boeing 737 MAX, a lot has to be done before the jet takes to the skies commercially.

Following 20 months of grounding, the FAA cleared the 737 MAX to return to the skies on November 18, 2020.  Aviation authorities across the globe temporarily suspended the aircraft’s type certificate after two fatal crashes in Indonesia and subsequently in Ethiopia. While the FAA was pretty much the last one to do so, it is the first to un-ground the aircraft as well.

But hold thy horses, as the 737 MAX has quite the way to go before it can fly passengers on commercial flights within the United States, or anywhere else for that matter.

Maintenance procedures

Between May 2017, when Malindo Air became the launch customer of the type, and March 2019, Boeing built and delivered 387 aircraft to customers across the globe. The largest number of 737 MAX aircraft was delivered to North America, including Mexico, where 166 of the global fleet has landed before the grounding. China remains a very important market as well, where Boeing delivered 81 MAXs – the second-largest market for delivered aircraft behind the US.

Prior to operating the aircraft, airlines will have to complete quite a few tasks. One of the most crucial ones is to complete the tasks in the Aircraft maintenance manual (AMM). For example, the AMM for a Boeing 737 Classic, an older generation of the aircraft, points out 44 references on how to put back the aircraft into serviceable condition after storage. On average, around 40 man-hours are required to make a stored aircraft airworthy once again, according to the British Women Pilots’ Association (BWPA).

For the Boeing 737 MAX, the final step of returning the aircraft to service requires an Operational Readiness Flight, according to Service Bulletin 737-00-1028. However, due to the background of the groundings, the procedure has a lot of added complexity.

Software and wire changes

The major work for airlines will be the installation of the revised software that would change the way that the Maneuvering Characteristics Augmentation System (MCAS) works. The controversial system, which has been at the forefront of attention throughout the grounding period, will be changed drastically.

Prior to the grounding, the MCAS relied on data from one Angle of Attack (AoA) sensor, without the redundancy of the other sensor located at the nose of the Boeing 737. The automatic system could also shoot off multiple times, slowing down the aircraft and result in an unrecoverable stall of the aircraft via the multiple nose-down movements.

Now, the MCAS will rely on data from both sensors. If the data is erroneous and disagrees by 5.5 degrees, the Speed Trim System (STS), including the MCAS, will be disabled for the remainder of the flight. Pilots will also be notified of the disagreement via the AoA DISAGREE alert and the disablement of the STS. Furthermore, the MCAS will only be able to fire off once per one event, rather than multiple times. The limited magnitude of the nose-down movement will “preserve the flight crew’s ability to control the airplane’s pitch by using only the control column,” read the FAA’s Airworthiness Directive (AD). An extra layer of redundancy is added by the Flight Control Computers (FCC) cross-monitoring each other, including the fact that it will now detect erroneous commands, including trim stabilizer commands.

The US-based authority also imposed the requirements for operators to change the horizontal stabilizer trim wire routing installations in order to prevent a short-circuit in the wiring, which could cause stabilizer trim runway.

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All in all, the FAA estimates that installing new software on the FCC, the revised MAX Display System (MDS) and the stabilizer wiring changes would cost up to $10,760 per aircraft, including parts and labor.

Flight manuals and training

The certifying authority also mandated changes to the Aircraft Flight Manual (AFM) and pilot training prior to the 737 MAX being able to once again serve passengers on commercial flights.

The AFM will see nine changes to various procedures, including what to do if such errors as the Airspeed Unreliable, Speed Trim Fail, AoA Disagree or ALT Disagree are displayed in the cockpit. The manual, which prior to the Lion Air flight JT610 crash did not include instructions on what to do in case of the MCAS causing un-commanded runway stabilizer movement. An emergency AD published by the FAA on November 7, 2020, a week after the Lion Air 737 MAX crashed into the sea near Indonesia, rectified that situation. Now, the AFM is expanded further, with additional instructions on what to do in various situations, including different problems with the runway stabilizer.

In addition to the changes to the AFM, pilot training has also been under scrutiny since the groundings. Initially, Boeing 737 NextGeneration (NG) pilots had to go through a theoretical lecture in order to be approved to fly the 737 MAX. In January 2020, Boeing shifted its position and recommended simulator-based training for the type’s pilots instead. The FAA affirmed this view with its latest notice, issued on November 18, 2020.

“Special training, including ground and flight training in a full flight simulator (FFS), is required prior to pilots operating the 737 MAX,” read the notice. In addition, the Flight Standardization Board (FSB) and Joint Operations Evaluation Board (JOEB) identified areas that pilots should pay extra attention to during their training. For example, the FSB report identified that future flight crews must complete training on such non-normal checklists (NNC) as issues with the runway stabilizer, errors like the AOA DISAGREE or ALT DISAGREE and training for MCAS.

Flying the Boeing 737 MAX

With the FAA being the last one out and last in regarding the grounding and subsequent un-grounding of the jet, US-based operators are so far scheduled to operate the type first. American Airlines (A1G) (AAL) is the most eager to do so, as it has scheduled flights for December 29, 2020. United Airlines and Southwest Airlines (LUV) indicated that they would fly the 737 MAX starting in Q1 2021 and Q2 2021, respectively.

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“In terms of next steps, we are taking a phased approach to return the aircraft to service. We will begin with non-commercial flights in early December before the official return to service date to demonstrate that the 737 MAX is as safe as every plane we fly at American,” read a letter by American Airlines (A1G) (AAL) chief operating officer (COO) David Seymour, including other Operations team executives.

The Dallas/Fort Worth-based carrier plans to gradually introduce throughout January 2021, eventually reaching up to 36 daily departures from its Miami International Airport (MIA) hub.

“As is always the case, safety is at the forefront of every decision we make. It’s with this unequivocal standard that we look forward to returning the 737 MAX to service,” added Seymour.

“Our Southwest Pilot Leadership Team has reviewed and expressed confidence in the MAX software and training updates following Boeing’s enhancements to the aircraft,” stated Southwest Airlines (LUV) chief executive officer and chairman (CEO) Gary Kelly, adding in that he was personally in touch with Boeing and the FAA to discuss the changes.

While the FAA cleared the Boeing 737 MAX to fly once again, other authorities across the globe are still in the process of doing so. For example, the European Union Aviation Safety Agency (EASA) plans to un-ground the aircraft only in late-2020 or early-2021.

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European Union Aviation Safety Agency (EASA) clarified the situation with the Boeing 737 MAX in Europe, indicating that there is a long way to go before the aircraft is once again allowed to fly in the continent.