maintenance

1. Human Performance
Maintenance Briefing Notes Human Performance and Limitations
Maintenance Briefing Notes
Human Performance
Human Performance and Limitations
I Introduction
With the traffic growth and increased demands upon aircraft utilization, the pressure of
maintenance operations on-time performance tends to increase. Consequently, there is
at present a growing need for an enhanced awareness of the importance of human
factors issues in aircraft maintenance.
The safety and effectiveness of airline operations are also becoming more directly
related to the performance of the people who maintain, inspect and service the aircraft
fleets.
The diverse nature of operations within today's complex aerospace industry gives rise
to dramatically different maintenance structures. With the dynamics of aviation
maintenance operations and the associated technician human factors there is a need to
understand the varying effects imposed by the unique maintenance environment.
The objectives of this Maintenance Briefing Note are:
• To provide the reader with an enhanced human factors awareness on aircraft
maintenance;
• To show how human capabilities and limitations can influence task performance and
safety within the maintenance environment; and,
• To guide the reader towards the related prevention strategies.
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2. Human Performance
Maintenance Briefing Notes Human Performance and Limitations
II Case Studies
To enhance awareness of maintenance operations this Maintenance Briefing Note
includes educational background coming with statistical data and case studies on
reported maintenance events, highlighting what happened, why it happened and what
can be done to avoid recurrence.
II.1 The source of case studies
Supplemental to the treatment of technical in-service reports by the Airbus Customer
Services Technical Support, a Maintenance Event Analysis Panel (MEAP) has been put in
place.
The role of the MEAP is to review all in-service events classified as significant related to
maintenance operations, and to conduct investigations in a broader perspective.
In order to view the problem from different angles, a wide range of experts
( representing domains such as human factors, flight safety, engineering, technical
data, maintenance engineering, maintenance training and some others ) are
participating to regular meetings.
Each significant maintenance event is investigated including considerations of potential
consequences in a different context, related maintenance and troubleshooting
instructions, scheduled maintenance tasks, and the environmental circumstances under
which the event happened.
Further to this analysis the MEAP has the authority to launch revisions to maintenance
manuals and tasks, ask for further investigations or propose technical changes if so
justified.
In each Maintenance Briefing Note we intend to share a real in-service event related to
maintenance activities, including the description of the event, possible reasons why it
occurred, and recommendations on how to avoid the re-occurrence.
The events investigated through the MEAP proceeding will be one source among others,
for these case studies.
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3. Human Performance
Maintenance Briefing Notes Human Performance and Limitations
III Statistical Data
Human failures are often recognized as being a contributor to incidents and accidents.
Technical and maintenance faults took over from CFIT as the biggest cause of fatal
airliner accidents. Some authorities consider that improper maintenance is now
contributing to a greater proportion of accidents than it did in the past. This is because
we did a lot to reduce CFIT.
Graphic 1 summarizes all the above.
Number Of Accidents
4 (12%)
11 (31%)
5 (15%)
7 (21%) 7 (21%)
Weather/icing Human Factors
Unknown Controlled Flight Into Terrain
Technical/Maintenance
( Source: Flight International – Airline Safety Review )
Graphic 1
Fatal Commercial Accidents Category / Main Causal Factor
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4. Human Performance
Maintenance Briefing Notes Human Performance and Limitations
IV Learning more about Human Factors in Maintenance Environment
The interaction between three factors affects human performance at work: the job,
the individual and the organization.
This means that, in a well-managed organization, taking the ideal situation:
Management within the
The Job is well designed to match Organization takes responsibility
known strengths and limitations of for all aspects of work and work
the person or team doing it. This design and encourages a good
includes: work areas, the safety culture by showing
environment, tools, materials, commitment and consulting the
machinery, control and display workforce when making decisions.
devices, management and A learning organization will take
communications systems and all into account the latest thinking on
technical documentation for best practice in safety and will
guidance and job control. learn from accidents and near
misses.
The company will also select
Individuals matched to the needs
of the job. (Fitting the human to the
job). They will have: the most
suitable physique (size, build and
strength), personality and
intelligence fitted to the job. They
will be fully competent by having the
right skills, understanding,
experience and training.
Figure 1
“The ideal World”
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5. Human Performance
Maintenance Briefing Notes Human Performance and Limitations
IV.1 Factors influencing the behavior of people at work
However, the management has to understand the influencing factors affecting
the behavior of people at work. Following are the main reasons why people do not
always perform their work properly:
The Environment:
• Weather inconvenience, extreme temperatures, high noise levels, inadequate
lightning, insufficient environment protection;
• Shift work: breaks across shifts, handover;
• Task characteristics: new, complex, confusing, rarely performed, requires good
memory, monotonous, etc.; and,
• Operational pressure: (time pressure, Customer pressure).
The Individual:
• Physical fatigue, synchronization (time zone, date/night shifts), medical conditions,
hearing, sight;
• Insufficiency of technical knowledge; and,
• Communication skills, moral, attitude towards work and colleagues.
The Organization:
• Procedures can be missing or are out of date;
• Unclear designed checklists;
• Not enough tools, inappropriate equipment;
• Aircraft design is not always good for maintainability; and,
• Lack of spare parts and relevant material.
Errors are possible in all maintenance tasks – some are more error-prone than others.
Human errors are major cause of accidents and can occur in all jobs – including
operations, maintenance, modification and management.
Does this mean that people have become more careless, forgetful, inattentive and
reckless over this period? Probably not, but it does reflect two important and
widespread trends:
• Aircraft components, along with most other items of equipment, have become both
more sophisticated and more reliable over the past three decades; and
• There is a growing appreciation that designers, manufacturers, corporate decision
makers, and maintenance managers can make mistakes which, in turn, create
the conditions promoting errors on the hangar floor.
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6. Human Performance
Maintenance Briefing Notes Human Performance and Limitations
Error is a normal component of human behavior. The trouble with an error in aviation
lies with the negative consequences it may generate in operational context. However,
we can trap the negative consequences before they produce damage.
Organizations can manage human errors by implementing re-active and pro-active
measures, and strategies.
V Origins of Human Error
The origins of human errors are generally differentiated by whether the error was
caused by the individual involved in the incident, by design features of the equipment
or procedures used by the individual which compelled them to make the mistake.
This focuses on determining whether the source of the human error was due to
the technician, which are attributed to such factors as individual choice of inaccurate
behavior, poor judgment or decisions, or generated by circumstances such as incorrect
or inadequate policies/procedures, equipment, design, and tooling, working conditions,
limitations or stressors.
V.1 Active failures versus latent failures
The main characteristic of maintenance errors is their lack of visibility. Maintenance
errors can remain silent for very long time in the system before producing visible
effects.
Active failures
Active failures are the result of unsafe acts (errors and violations) committed by those
at the quot;sharp endquot; of the system. In the case of active failures, the negative outcome is
almost immediate.
Latent failures
Latent failures are created as the result of decisions, taken at the higher echelons of the
organization. Their damaging consequences can take a long time to reveal themselves,
sometimes many years, only becoming evident when they combine with local triggering
factors (e.g., errors, violations and local conditions) to breach
the system's defenses.
That is often the case for latent failures that cause or contribute to maintenance errors.
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7. Human Performance
Maintenance Briefing Notes Human Performance and Limitations
V.2 Some local triggering factors that impact maintenance activities
The aircraft engineer is the central part of the aircraft maintenance system.
It is therefore very useful to be aware of the factors which affect maintenance activities.
Knowledge, skills, experience:
• Being unfamiliar with a failure report or aircraft type;
• Lack of specific training or skills;
• Inappropriate experience for a job; and,
• Changes in aircraft type with no experience compared to past routines or
expectations, etc.
Familiarity/Routine job with:
• The task;
• Safety procedures;
• Ground Support Equipment (GSE) and tools (availability, quality, location, delivery
and/or collection, identification, handling heavy or awkward items, etc.); and,
• Paperwork (unavailability of relevant manuals or procedures, failures to complete
paperwork correctly, etc.).
Morale:
• Personality conflicts;
• Being unhappy with the work situation; and,
• Inadequate incentives/motivations .
Support:
• Difficulties with support from other areas; and,
• People unavailable in other areas, insufficiency of manpower.
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8. Human Performance
Maintenance Briefing Notes Human Performance and Limitations
Fatigue:
• Problems with tiredness, unusually slow working;
• Disturbed sleep patterns, particularly at the beginning of a shift; and,
• The balance between work and rest.
Pressure / Time constraints:
• High workload;
• The workforce being spread too thinly over the jobs;
• Many interruptions;
• Too little time to perform the job; and,
• Pressure of flight schedule.
Shifts working:
• Difficulties with shift patterns, time of day or night; and,
• Communication at shift handover.
Environment:
• Weather inconveniences;
• High noise levels;
• Inadequate lighting; and,
• Insufficient environmental protection, etc.
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9. Human Performance
Maintenance Briefing Notes Human Performance and Limitations
VI Prevention of Human Failures in Maintenance Activities
A series of Human Factor problems form an error chain. If any one of the links in this
chain had been broken the incident may have been prevented. It might be done by
building in measures/defenses, which may not permit an error at one or more of
the stages. A good example is J.Reason’s ‘Swiss Cheese’ Model, here below.
Maintenance-
related event
Defenses
Inadequate
Productive Activities
Unsafe Acts
Preconditions
Line Management
Deficiencies
Decision Makers
Fallible decisions
Figure 2
J.Reason’s ‘Swiss Cheese’ Model
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10. Human Performance
Maintenance Briefing Notes Human Performance and Limitations
VI.1 Situational Awareness or “Knowing What Is Going Around You”
Definition
Situational awareness is a synthesis of an accurate up-to-date mental model of one’s
environment and state. That means perceiving important elements (for example,
feeling the cold as you walk outside on a winter morning), understanding their meaning
(understanding there may be black ice on roads), and projecting this status
into the future (appreciating that such conditions could cause the car to skid and
consequently adapting your driving speed).
The process of attention, perception and judgment should result in awareness of
current situation.
The aircraft maintenance engineer must be aware of:
• Who is working around the aircraft to avoid injuries;
• The status of the system he/she is working on;
• The relationship between the reported effect and the intended rectification;
• The possible effect of this work on other systems; and,
• Consequence of his/her own actions for the others.
In aircraft maintenance engineering, the entire team needs to have situational
awareness, not just of what they are individually doing, but of their colleagues’
activities as well.
VI.2 Use of maintenance check list: what is involved in maintenance
environment
In order to manage maintenance well, you should be able to match the issues below.
The challenges for maintenance management:
• Be fully aware of which maintenance work can lead to a major risk;
• Put in place good defenses/protection to make sure these accidents are very
unlikely, including:
o Safety notices and devices;
o Quality controls (permits, procedures, checklists);
o Management controls (supervision and checking of tasks);
o Highly competent maintenance teams; and,
o Well-designed maintenance planning.
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11. Human Performance
Maintenance Briefing Notes Human Performance and Limitations
• Base your maintenance program on major accident risk assessment;
• Communicate well during shifts and between shifts;
• Take special care of temporary or inexperienced maintenance technicians and
contractors;
• Do walk around inspections of maintenance tasks in progress;
• Look for early signs of problems (e.g. a large backlog of jobs; excessive repair
times; adverse feedback from staff); and,
• Investigate near misses and accidents while learning from failure.
VII Case study
VII.1 Description of the event
An operator performed a scheduled slide deployment test on doors 1L, 2L, 3L, and 4L.
Two of the doors 1L and 4L didn’t automatically open and required manual opening with
subsequent successful slide deployment. However, the operator’s engineering
department noticed that pressure was still within the green band on both
the emergency actuators and the diaphragms were not punctured meaning that
the actuators did not operate.
Upon further inspection it was found that the percussion mechanism on both of the
actuators were not correctly positioned and locked.
VII.2 Findings
When the arming lever is placed in the ARMED position the activation lever moves
under the release lever of the percussion mechanism on the actuator.
If the door is then opened in ARMED mode the door lifts and the activation lever
operates the release lever which in turn punctures the diaphragm in the reservoir to
operate the actuator.
Refer to Figure 2, on Page 12.
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12. Human Performance
Maintenance Briefing Notes Human Performance and Limitations
Release Lever
Activation Lever
Figure 3
Door Emergency Actuation Mechanism
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13. Human Performance
Maintenance Briefing Notes Human Performance and Limitations
Door 1L –Emergency Actuator Percussion Mechanism – Release Lever Position
Release lever was not placed in the correct fully extended position. A gap can be seen
under the knurled screw.
Incorrect wire locking. Instead,
should be locked to this point
here.
Door 4L –Emergency Actuator Percussion Mechanism – Release Lever Position
Release lever was not placed in the correct fully extended position. A gap can be seen
under the knurled screw.
Incorrect wire locking. Instead,
should be locked to this point
here.
Familiarity with Maintenance
Manual procedures and
illustrations
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14. Human Performance
Maintenance Briefing Notes Human Performance and Limitations
VII.3 Recommendations
• In order to reactivate the percussion mechanism, the following steps have to be
accomplished:
- Push release lever to the fully extended position against the spring and hold it;
- Tighten the knurled screw, fully engaged in the bore of the release lever; and,
- Safety the knurled screw by wire locking to the lug provided on the release lever.
Release lever placed in the correct fully
extended position with the knurled screw
engaged and tightened
• In order to avoid similar issues in the future, a caution has been included in
the relevant AMM tasks to highlight that if the release lever is not placed in the
correct position then the emergency actuator will not operate correctly when the
door is operated in emergency mode.
Familiarization with
procedures and
supervision/checking of
performed tasks
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15. Human Performance
Maintenance Briefing Notes Human Performance and Limitations
It is very important to read Warnings and Cautions.
WARNING: calls to use of materials, processes, methods, procedures, or limits which
must be followed precisely to avoid injury to persons.
CAUTION: calls attention to methods and procedures which must be followed to avoid
damage to equipment.
VIII Summary of Key Points
Since people design, build, operate, maintain, and manage potentially hazardous
technologies, it is hardly surprising that their decisions and actions contribute, in one
way or another, to unwanted events. However, mistakes made must be an occasion to
learn from error in order to prevent these undesired events.
Reminder of the main factors, leading to incite an error:
• The nature of the workplace;
• The quality of tools and equipment;
• Whether or not supervisors or managers turn a ‘blind eye’ in order to get the job
done;
• The quality of the rules, regulations and procedures; and,
• The organization’s overall safety culture, or indeed its absence.
This Maintenance Briefing Note (MBN) is part of a set of Briefing Notes that provide an overview of the applicable standards,
techniques, best practices, human factors, suggested company prevention strategies and personal lines-of-defense related to
major threats and hazards that may affect maintenance.
This MBN is intended to enhance the reader's safety awareness but it shall not supersede the applicable regulations and the
Airbus or airline's maintenance documentation; should any deviation appear between this MBN and the Airbus or airline’s
maintenance documentation, the latter shall prevail at all times.
In the interest of aviation safety, this MBN may be reproduced in whole or in part - in all media - or translated; any use of
this MBN shall not modify its contents or alter an excerpt from its original context. Any commercial use is strictly excluded.
All uses shall credit Airbus.
Airbus shall have no liability or responsibility for the use of this MBN, the correctness of the duplication, adaptation or
translation and for the updating and revision of any duplicated version.
Airbus Customer Services
Maintenance Engineering Services
1 Rond Point Maurice Bellonte - 31707 BLAGNAC CEDEX FRANCE
MBN Reference : MAINT – HUM_PER – SEQ 01 – REV 01 – NOV. 2006
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