Maintenance Workload

When people discuss workload in aircraft maintenance, they can be viewing the subject from two different perspectives:

• workload required, expected, planned for, and experienced by the maintenance organisation, or
• workload demanded of, and experienced by, individual maintenance employees.

Both organisational and human factors impact each other, and it is the responsibility of the maintenance organisation to ensure that manpower available is more than adequate to meet all necessary tasks.

Aircraft Maintenance

The role of aircraft maintenance, simply put, is to ensure that aircraft presented “on the line” for flight operations comply with:

• all legal requirements (e.g. continuing airworthiness requirements, airworthiness directives (ADs), certificate of release to service, type certificate and supplementary type certificate),
• operational equipage requirements (e.g. oxygen systems, first aid, and flotation devices), and
• appropriate equipment for the type of operation being flown (e.g. communication, navigation and surveillance).

Furthermore, where maintenance is conducted under contract by a third-party maintenance and repair organisation, each airline customer may have other specific requirements (e.g. additional safety features, technical solutions, and issues such as in-flight entertainment and seating).

Planned Workload

All of the tasks mentioned above can be clearly defined – what to do, when to do it, how often, how to do it, and what to do it with. These will be presented in the approved maintenance programme and manual; these tasks define the majority of the maintenance workload and can be planned for and scheduled. For example, the completion of various inspections and checks (A, C & D checks) is a legal requirement that must be fulfilled within limits of numbers of flight cycles, hours flown and/or time expired since previous inspection or check. These limits will vary between aircraft types and models, as will the contents of each inspection and check.

To fulfil the operational flying programme, some inspections and checks (and elements thereof) can be brought forward in time and/or conducted more frequently. In this way a maintenance organisation (or department) managing a mixed fleet of aircraft will be able to spread workload and programme “blocks of time” months and even years into the future for specific activities.

Aircraft and equipment manufacturers will provide operators with details of manpower requirements for specific tasks, from changing nosewheel tyres to flushing and cleaning hydraulic systems. Furthermore, in addition to these details, experience will guide maintenance organisations in predicting quite accurately the number of workers they require for each and every planned task and how long it will take them, e.g. preflight might be 2 technicians for 90-minutes; postflight may require two workers for 2 hours, and an A-check could take them 21 hours.

Unplanned Workload

Other day-to-day tasks will arise on demand, in response to feedback from flight crews or observations made during routine maintenance inspections and line maintenance tasks. These tasks cannot be specifically planned for, but the workload involved can be roughly estimated. From experience this can demand as much as 50% of the planned effort, i.e. manpower and time – often given in units of FTE (full time equivalent).

Situations can arise in response to commercial activities which will impact on the planned workload, such as the temporary leasing-in of an aircraft, or the need to switch aircraft types between operations (routes/tasks). These unplanned events can be for short intense periods, or have much longer and deeper repercussions.

Finally, special unplanned maintenance activities are often required in response to Service Bulletins from manufacturers and ADs from regulatory and oversight authorities.

Subjective Workload

All of the above has to be achieved by manpower (planners, supervisors, licensed engineers and technicians etc.), within a timeframe, and utilising various resources (hardware and software) within fixed and/or mobile facilities. So, maintenance workload can also refer to the subjective viewpoints of each and every worker, team, department (shop) and shift, involved in fulfilling the required tasks.

Fleet Composition

The size and diversity of an airline’s fleet, or the range of aircraft a maintenance organisation is contracted to work on, have a direct impact on workload.

It is common for airlines to operate several types, models, and generations of aircraft. This requires a broad range of skills, knowledge, and experience. Ageing aircraft require increased inspection activities and maintenance tasks, which increases workload whilst new aircraft present ever-increasing complex and new technologies.

Balancing Resources to meet the Workload

It is essential that maintenance organisations implement a functional system for:

• comparing planned workload with available resources (human and otherwise),
• managing human resources so that individual and team capacities (mental and physical skills, knowledge and attitudes) will be “as expected” and not severly deteriorated due to fatigue, etc.,
• coordinating the availability of suitable and necessary facilities and equipment, etc.
• predicting levels and types of unplanned workload, and
• rapidly reacting to shortfalls when they occur.

This system needs to be underpinned by an effective performance feedback mechanism (reporting, meetings, briefings, training etc).

Fatigue and Shift Patterns

In balancing maintenance workload against workers’ capacities, consideration must be given to human factors, including Fatigue and Stress. Fatigue, in particular, needs to be managed through an effective scheduling and rostering system that aims to prevent the onset of fatigue, and also responds to symptoms of fatigue manifest in the workplace. Maintenance of aircraft often occurs at night and at weekends to ensure that flying programmes which commence early mornings can be fulfilled. However, increasing numbers of airlines run flying schedules 24 hours a day and 7 days a week.

Rotating shift work and working at night impact physical, mental and emotional performance, and therefore, reduce a persons maximum workload capacity. The effects can be both short and long term.

There will always be a commercial pressure to maximise efficiency and reduce costs. As aircraft, engines, and equipment all become more efficient and reliable, two key indicators become more prominent:

• labour costs become a greater (perhaps the greatest) cost for a maintenance organisation, and
• the human becomes the biggest source of error.

Therefore, any drive to reduce labour costs beyond a critical point will increase risk and the costs associated with losses from incidents and accidents. For example, in every daily/nightly shift there is “dead” time at the beginning and end, therefore the pressure is to increase shift periods, thereby reducing the percentage of unproductive time. However, increasing shift periods increases the risk of short-term fatigue and reduced vigilance and performance.

Shift planning, rotating, and rostering need to be scientifically based to maximise resources, and will benefit from being integrated with a Fatigue Risk Management System (FRMS). Consideration needs to be given to:

• time of shift start/finish
• length of shift
• rest periods and refreshment/nutrition breaks during a shift
• tour of duty (number of days/nights on shift)
• days off
• days/time “on call/standby”
• changes in shift pattern

Because, as already mentioned above, some unplanned workload may exceed the predicted contingency, maintenance organisations will rely on the use of overtime for high-workload periods. The impact of unplanned overtime needs to be monitored and kept within boundaries.

Human Factors Affecting Subjective Workload

Many factors affect a person’s workload capacity, including:

• level of experience, knowledge, and skill
• familiarity and level of confidence
• workspace design – does the “layout” and access to tools, equipment, documents and support, help or hinder the worker, and does it offer adequate protection
• levels of fatigue and stress
• health issues
• sleep debt
• circadian cycle – usually the early hours correspond with a lowered capacity
• off-duty activities – it is common for shift workers to hold second jobs

Because some of these factors are personal and subjective, and therefore cannot be measured, it is important that to gain useful feedback and reduce risk, organisations support workers in self-assessment and self-reporting.

Organisational Factors Affecting Workload

Many factors affect an organisation’s ability to meet its workload demands, including:

• staff shortages – in numbers but also in specialist roles
• low levels of experience, knowledge and skills throughout the workforce
• lack of, or unavailability of, facilities and other resources
• equipment malfunction or failure
• nonexistent, or inadequate task analyses – matching manpower (FTE) with each tasks to enhance shift planning and also aiding workspace design to assist workflow
• poor culture, including leadership, supervision and teamwork
• extreme ebbs and flows in peak/off-peak workload – i.e. an inability to plan and spread workload effectively

Managing Organisation and Personal Workload

With continuous commercial pressure to reduce manpower costs, it is important that maintenance organisations take proactive measures to manage workload effectively so that it does not threaten safety of aircraft, employees, or the business. Such measures can include the following:

• task analysis to assist:
  • allocation of adequate personnel to each task
  • design of workspace to aid workflow
  • allocation of appropriate resources for each task, including supervision
  • provision of a protective and conducive workplace environment
• scheduling for planned and unplanned workload
• controlling and monitoring the use of overtime
• integrating a Fatigue Risk Management System (FRMS) into employee shift allocation, scheduling and rostering
• cultivating a positive safety culture
• providing appropriate knowledge and skills training, including human factors
• facilitating an effective feedback system to measure symptoms of poor workload management
• providing adequate time, opportunities and facilities for rest and nutrition during the working day/night

Accidents & Incidents

• B733, Paris CDG, 2011. (Contributing to the accident were: poor resource planning caused overstretching of the personnel’s capacities when unexpected extra work turned up, this generated increased time pressure that led to things being forgotten and approximate execution of the work cards; and, the supervisor had worked for an excessive number of hours over a long period of time, which lowered his performance and his aptitude to carry out checks efficiently.
• B734, near Daventry, 1995. (Amongst the topics of concern to the CAA were a lack of presence of Quality Assurance Engineers during night shifts; this was a matter of persistent concern for two years.)
• B737, in the vicinity of Norfolk, England, 2009. (It is recommended that the European Aviation Safety Agency review the regulations and guidance in OPS 1, Part M and Part 145 to ensure they adequately address complex, multi-tier, sub-contract maintenance and operational arrangements. The need for assessment of the overall organisational structure, interfaces, procedures, roles, responsibilities and qualifications/competency of key personnel across all sub-contract levels within such arrangements should be highlighted.)

Further Reading

• Human Factors in Aircraft Maintenance, Colin G. Drury, State University of New York
• Operator's Manual: Human Factors in Aviation Maintenance, FAA, 2014
• Advisory Circular 120-115: Maintainer Fatigue Risk Management, FAA, 2016
• Safety Behaviours: Human Factors Resource Guide for Engineers, CASA (Australia), 2013