Boeing Max 737: The Case Study

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Airlines are vulnerable to macroeconomic conditions because of their global footprint. Due to the COVID-19 pandemic, the aviation industry’s business environment has been characterised by economic and geopolitical tensions. These tensions have caused a series of market and financial disruptions that have seen aircraft go into preservation. However, recently, the United Arab Emirates announced its plan to approve the return of dormant Boeing’s 737 MAX planes to service (Odeh, 2020). Air carriers’ fundamental responsibility is to ensure that the aircraft is airworthy before the aeroplanes return to active operation. This paper evaluates the current regulations of aircraft and crew licenses; it incorporates recommendations to airlines, regulatory authorities and personnel to ensure that the Boeing Max 737 returns safely to service.

Existing Regulations

GCAA (Operations regulations, no date)

  • Aircraft operators cannot operate the plane unless an approved organisation has maintained and endorsed its service return.
  • The approved organisation should regularly inspect and service aircraft components and comply with the aircraft manufacturer’s maintenance manual.
  • In the absence of a manufacturer’s maintenance manual, maintenance personnel should refer to the airworthiness standards and procedures outlined by GCAA. The maintenance manual should contain practices, techniques, and methods to maintain the aircraft’s structure and components that have been approved by GCAA.
  • Before installing any component to a preserved aircraft, the maintenance organization should ensure that they are eligible to be fitted when new airworthiness directives are issued.
  • Both raw and consumable materials used in maintenance must be documented and be traceable.

The Recency of Crew License

  • A pilot cannot operate a plane unless he has conducted at least three take-offs and landings in the last 90 days as a pilot of the same type/class of the airplane.
  • A pilot can only operate the plane at night if he/she has a valid instrument rating and must have conducted at least one-night landing in the last 90 days.
  • A pilot who has undertaken a Zero Flight Time Training (ZFTT) course and has approved take-offs and landings must commence operation within 21 days of approval. If the take-offs and landings are not instigated within 21 days, the operator should take refresher training.
  • The 90 days can be extended to 120 days if the pilot operates under supervision or an examiner.
  • Recent experience is not required for Cruise Relief Co-Pilots. However, they must have a refresher course every 90 days.
  • All flight crews are subject to recurrent training every six months.


Preservation of Aircraft (Section 38 safety assurance system, 2019)

  • The aircraft’s storage program should be specific to the design and characteristics of the plane in question. The aircraft’s preservation level should be appropriate for variables such as the length of storage, design features, and storage environment type.
  • The aircraft’s manufacturer should prepare storage programs for the plane. However, if the airline has specific maintenance requirements for a particular plane, it can use its maintenance manual.
  • The airline can prevent the effects of a non-operational aircraft by implementing appropriate preservation levels. Storage levels include short-term storage (non-operational for less than 60 days), intermediate (non-operational for 61-120 days), and long-term storage (more than 120 days). The level of preservation should be per the provisions of the FAA maintenance programs.
  • The storage program should be documented as stipulated by part 43 and 43.13(c) of the storage maintenance program.
  • If the airline removes parts from a stored aircraft, the liability of ensuring the removed parts’ safety lies on the airline.
  • The airline must document the maintenance process of the removed parts and provide them to aviation safety inspectors.

The Recency of Crew Licenses

An Airman should not conduct any operation that he/she is authorised to do unless they have completed the procedure within the flag calendar’s stipulated time. A domestic, flag or commuter airmen can only operate if they have conducted the operation within 30 days. For on-demand or supplemental services, the airmen must have undertaken such activities within 90 days. This regulation does not apply to airmen who have conducted additional services in the last 30 days.

Suppose an authorised operation does not satisfy the calendar requirements; in that case, he/she can be allowed to operate only if they advise the administrator of their recency status at least five consecutive days before the continuation of the operation. FAA can also permit an airman who does not meet the recency requirements to operate if they avail themselves to the organization five consecutive days before the continuation of operation for the re-examination of their eligibility.


Preservation of Aircraft (Easy access rules for airworthiness, 2020)

  • The aircraft’s storage should be protected from debris, dirt, and dust.
  • All aircraft components should be protected from extreme environmental conditions.
  • Measures should be taken to protect items that are sensitive to light from direct sunlight.
  • Items that can emit fumes or radiation, e.g., wet batteries and magnetic items, should be segregated from the aircraft’s component.
  • Consideration should be made for parts separated from the aircraft during maintenance activities.

The Recency of Crew License (Flight Crew Licenses,2018)

Lightplane license holders of group A, H, S, and B can operate only if:

  • Acted as airplane pilots in the last 24 months
  • Have a minimum of a one-hour flight time refresher training with an instructor
  • At least 12 hours of flight time (must include take-offs and landings) as a pilot in command (PIC).

Sailplanes and powered sailplanes (SPL) holders can operate only if:

  • They have been in operation over the last 24 months, has 5 hours flight time, has15 launches, and two refresher training with an instructor.
  • TMG holders of SPL can operate if they have completed a TMG course in the last 24 months, 12 hours flight time, and a minimum of a 1-hour refresher training with an instructor.

Balloon Pilot License Holder

License holders can operate only if they have:

  • Operated in the last 24 months, 6 hours of flight time, and one training with an instructor.
  • License holders qualified to fly multiple balloons must have completed a minimum of 3 hours of flight time during training within the last 24 months.

All license holders who do not meet their specific class requirements should have a proficiency check with an examiner before resuming operation. Alternatively, they can conduct additional take-offs and landings with an instructor’s supervision.

Original Equipment Manufacturer (OEM) recommendations for Boeing 737 MAX (Preliminary summary, 2020)

  • Because some 737 MAX airplanes have a single AOA sensor, manufacturers should ensure that this feature will not interfere with the aircraft’s flight and landing.
  • The manufacturer should change the flight controls to ensure that a single nose-down command is generated when Manoeuvring Characteristics Augmentation System (MCAS) is activated.
  • The aircraft should stop the commanding stabilizer movement to allow adequate elevator movement for pilot control of the aircraft’s pitch attitude.
  • Develop a display software system that will alert the flight crew when the left and right AOA Sensors disagree.
  • Implement an FCC cross monitor that can detect and shut down faulty stabilizer runaway commands.
  • The manufacturing companies should consider a mandatory implementation of safety management systems instead of the current voluntary implementation.
  • The manufacturer should integrate system safety analyses in the design assurance process.
  • The use of all available aviation data should be considered during the development of corrective actions to enhance aviation safety. Operational data should be available and accessible from a single data repository system.

Each regulatory body mentioned above has a specific set of stipulations that outline the applicable directives regarding aircraft maneuver. The ordinances delineated by these organizations distinguish the crucial capabilities, performance measures, associated requirements, and the series or process of actions to be implemented to trigger the attainment of desirable outcomes. For instance, the GCAA highlights an approved institution’s need to maintain and endorse a plane’s service return before its use by aircraft operators.

The FAA emphasizes the importance of developing proper preservation levels for non-operational aircraft to maintain its functioning capacity after a period of inactivity. On the other hand, the EASA guidelines underscore the importance of preventing the impact of environmental conditions on aircraft when in a non-operational state. The above-mentioned decrees address deficiencies in mission areas, evolving threats or applications, and system cost improvements. Furthermore, they highlight the required competencies for aircraft operators.

Gaps in the Current Regulations/Policies

Review of Safety by Design

The maintenance of the aircraft involves structural, components, and service maintenance. Structural maintenance involves seeking structural deterioration sources such as susceptibility of its structure to accident damage, fatigue damage, and environmental deterioration. Boeing 737 MAX is a single-aisle jet equipped with a CFM LEAP-1B engine. During a double engine failure or a hydraulic failure, flight controls of the aircraft are automatically and seamlessly reverted to normal through servo tabs (Singh, 2019).

The plane’s MCAS prevents aerodynamic conditions such as stalling that might destabilize the plane (Singh, 2019). However, MCAS’s key weakness is that it relies on only one of the plane’s angle of attack (AOA) sensors. Regulatory bodies assessed the aircraft’s AOA sensors and revealed that the MCAS commands could make the aircraft’s horizontal stabilizer move at a fixed rate, regardless of the stabilizer’s position. These events caused many mistrim conditions, making it difficult for the flight crew to mitigate them using elevator control.

Apart from the AOA sensors, another safety issue caused by the aircraft’s design is its winglet type does not meet regulatory requirements. In collaboration with EASA, FAA discovered that the aircraft’s beacon’s preferred installation location was discordant with ICAO’s requirements for empennage and wing exclusion. Further analysis showed that this structural hitch was why a similar plane could not be detected in the water after an accident (Effects of novel coronavirus, 2020). An aircraft’s beacon helps to detect a plane’s position during the event of a water accident. The Airworthiness Standards (2016) mandates that the wing flap controls be designed so that the flap will not move from the designated position unless an automatic flap load limiting device adjusts the control. The Boeing 737 MAX wing flap controls have not met these requirements.

Review of the Airworthiness Aircraft’s Operation and Maintenance

The Boeing 737 MAX uses a speed trim system (STS) to move the horizontal stabilizer in response to airspeed changes automatically. The STS increases the stability of the aircraft’s speed, which satisfies the certification regulation of the FAA. However, because the aircraft’s LEAP-1B engines are larger and more powerful than the predecessor models, they have been positioned further forward the plane than the latter. FAA regulations require that the push force allows for a pushover manoeuvre of a zero-g load factor.

The aircraft should be able to recover from an operation without exceeding a pull force of 50 pounds. However, in the absence of the newly-incorporated MCAS function, the LEAP-1B engine of the Boeing 737 MAX makes the aircraft feel much lighter than regulatory bodies permit it. Even with the increased speed stability provided by the aircraft’s MCAS and STS, regulatory bodies still require the aircraft to have a high pull-force feel independent of MCAS and STS’s help. In addition to the LEAP-1B engines, another key issue is that the aircraft’s STS failure modes depend on the pilot’s immediate actions and skills. The reliance on pilot’s reaction poses a serious operational threat and should be addressed.

Review Current Maintenance Program and Advice Changes Required

The following maintenance procedures are undertaken to protect the aircraft during storage: The maintenance program considers the environmental conditions (humidity, pollutants, etc.) of the storage area. According to the plane’s maintenance manual, when the temperatures are subzero, the risk of the aircraft’ tires sticking to the ground is high (Bogaisky, 2019). The aircraft’s manufacturer advises air carriers to place coarse sand under the tires, wheels and brakes assemblies to prevent them from being corroded by the effects of snow, humidity, and rain (Bogaisky, 2019). Among other recommendations, the Boeing 737 MAX maintenance manual also recommends using yellow 3M vinyl tape to seal and protect the aircraft’s gaps, lubricants, and sensors.

The Leap-1B engines are powered up once every week for 15 to 20 minutes. The engine powering vaporizes the moisture in the oil and fuel system and covers the engine with oil, preventing corrosion (Bogaisky, 2019). The flight computers and auxiliary power units are rebooted once every week. Since the aircraft have been stored under hot temperatures, the planes’ doors are regularly opened to allow for adequate air circulation. Sensitive aircraft’ parts such as the batteries are removed to protect them from corrosion and deterioration.

The oil of the aircraft is drained and replaced with an anti-corrosive oil solution. Desiccant bags – anti-moisture packets- are placed in the inlets to monitor the plane’s humidity level. For planes that have been dormant for over 60 days, the vinyl tape is used to seal fuselage gaps and protective coating sprayed over unpainted metallic surfaces. Windows and cockpit windshields are covered with reflective material (Electronic code of federal regulations, 2020).

Cotton covers are put under seats and runners to protect them from mildew. Water is drained from fuel tank sumps to protect the aircraft from the growth of microorganisms. The rudder, flaps, and control services are exercised every 90 days. The landing gear’s flexing is done while the aircraft is bolstered on jacks placed under its wings and nose. The flexing is done for aircraft that have been in preservation for over one year.

Every 90 days, the flaps, rudder, and other control services are exercised. Despite the rigorous maintenance activities, the aircraft’s owners and operators must consider regulatory bodies’ recommendations. The aircraft needs to comply with regulatory bodies’ correct corrective actions to become airworthy. In this regard, it is recommended that the air carrier ensures that the AOA sensors are correctly calibrated to improve its airworthiness.

Since miscalibration of the AOA can result in sensor failure, the aircraft operators should aim for precision in calibration to optimize its efficiency. According to FAA, AOA sensors can be damaged during normal aircraft operations; and, therefore, they should be addressed during maintenance and servicing operations (Broderick, S., 2019). Maintenance of AOA sensors is considered a non-specific continued airworthiness maintenance activity.

Review of the Current Licensing Program and Advise Changes Required

Calendar and flight-based activities are currently out of sync because the airplanes are still in storage. Given that the craft has made significant operational and structural changes, the aircrew needs to be retrained. A new training program has already been proposed for the aircraft’s crew and is still awaiting approval from relevant bodies. The new training program aims to improve the flight crew’s recognition and response to stabilizer movements caused by the plane’s modifications. In the same regard, it is recommended that UGCAA mandates that flight crew receives retraining on all revised design changes before license renewal. The training on the revised design changes of the aircraft should be complementary to the normal re-licensing requirements.

Critical Analysis/Evaluation of Current Regulations

During a normal operation of a plane, the accuracy of AOA values is detected by the Air Data Inertial Reference Unit (ADIRU). The electrical transmission circuits include wiring between AOA sensors and ADIRU and wiring the AOA circuits. When the electrical circuits have failed, the ADIRU will detect the failure and, therefore, will not transmit the data. However, some failures of the AOA sensors do not arise from degraded or malfunctioning electrical circuits.

The mishap described above causes the ADIRU to transmit the AOA values as valid when, in real sense, they are inaccurate. Miscalibrated AOAs are responsible for these kinds of situations when one of the aircraft’s AOA sensor value exceeds another by 5.5 degrees (FAA, 2020). Evidence shows that because of the Boeing 737 Max’s biased AOA sensors, the plane’s vane angle values are misaligned (Preliminary summary, 2020).

For example, when the vane of the aircraft is at the zero position, the SMYD displayed at -31.9° rather than the permitted 0° ± 5° b (Preliminary summary, 2020). When the vane of the aircraft is at its maximum position, the SMYD displayed at -67.6° rather than the permitted +100° ± 5° c (Preliminary summary, 2020). The Six-Sigma model asserts that a business process can be improved when a business reduces the probability of errors to a minimum.

According to the ideology, quality control can be achieved by assessing quantitative measures and statistical improvements. Therefore, the aircraft’s owners and operators should reduce the probability of error of the AOA values to the lowest permitted values to achieve maximum quality levels. Improving the calibration of the AOA sensors will improve the accuracy of transmission of AOA sensor values, which, in turn, will improve the safety of the aircraft upon its return to service. I recommend that the GCAA creates a new certification requirement that mandates the maintenance of the AOA sensors during normal maintenance and servicing activities.


A major downside of obtaining precise measurements of AOA sensors is that it is time-consuming. A study conducted by Rodríguez-Navarro et al. (2018) shows that calibration is time-consuming and requires specific infrastructure to achieve precision. The reliance on specific calibration infrastructure increases calibration costs. Given the economic loss endured by air carriers during the pandemic, aircraft operators and owners may be reluctant to implement this recommendation coupled with the high calibration costs. However, Moghaddasi, Djerafi, and Wu (2017) developed a model and a calibration method that is simple, cost-effective, and results in operational accuracy. The aircraft’s operators can adopt this calibration technique to cut down on calibration costs.


While regulatory bodies consider the return to service of the Boeing 737 Max, the aircraft’s operators should consider the airworthiness directives. The aircraft manufacturers can improve the AOA sensor calibration to improve the accuracy of transmission of AOA sensor values.

Since AOA sensors can be damaged during normal aircraft operations, the operators should ensure maintenance and servicing of the sensors during normal maintenance activities. Instead of considering AOA sensors’ maintenance as a non-specific airworthiness maintenance activity, it should be made mandatory. GCAA should create a new certification requirement that mandates the AOA sensors’ sustenance during normal maintenance and servicing activities. Flight crew should receive retraining on revised design changes of the aircraft before license renewal.

Reference List

Airworthiness standards: normal, utility, acrobatic, and commuter category airplanes (2016). Web.

Bogaisky, J. (2019) ‘How airlines are defending dormant 737 MAX jets from the ravages of corrosion, insects and time’. Forbes. Web.

Broderick, S. (2019) More angles on FAA InFO about the AOA sensor. Web.

Easy access rules for airworthiness and environmental certification (regulation (EU) no. 748/2012). (2020). Web.

Effects of novel coronavirus (COVID‐19) on civil aviation: economic impact analysis (2020). Web.

Electronic code of federal regulations (eCFR). (2020). Web.

Flight crew licenses. (no date). Web.

Moghaddasi, J., Djerafi, T. and Wu, K. (2017) ‘Multiport interferometer-enabled 2-d angle of arrival (AOA) estimation system’, IEEE Transactions on Microwave Theory and Techniques, 65(5), pp. 1767–1779. Web.

Odeh, L. (2020) ‘UAE approval of Boeing 737 Max likely to closely follow FAA’, Bloomberg. Web.

Operations regulations: commercial and private air transportation. (no date). Web.

Preliminary summary of the FAA’s review of the Boeing 737 MAX (2020). Web.

Rodríguez-Navarro, D., Lázaro-Galilea, J.L., Espinosa, F., De-La-Llana-Calvo, A. and Santos, C. (2018) ‘Simplified calibration process for a PSD-based optical IPS’, 2018 International Conference on Indoor Positioning and Indoor Navigation (IPIN), Nantes, pp. 1–6.

Singh, S. (2019). Technicalities of Boeing 737 maintenance. Web.

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