| The term "human factors"
has grown increasingly popular as the commercial aviation industry
has realized that human error, rather than mechanical failure, underlies
most aviation accidents and incidents. If interpreted narrowly, human
factors is often considered synonymous with crew resource management
(CRM) or maintenance resource management (MRM). However, it is much
broader in both its knowledge base and scope. Human factors involves
gathering information about human abilities, limitations, and other
characteristics and applying it to tools, machines, systems, tasks,
jobs, and environments to produce safe, comfortable, and effective
human use. In aviation, human factors is dedicated to better understanding
how humans can most safely and efficiently be integrated with the
technology. That understanding is then translated into design, training,
policies, or procedures to help humans perform better.
Despite rapid gains in technology,
humans are ultimately responsible for ensuring the success and safety
of the aviation industry. They must continue to be knowledgeable,
flexible, dedicated, and efficient while exercising good judgment.
Meanwhile, the industry continues to make major investments in training,
equipment, and systems that have long-term implications. Because
technology continues to evolve faster than the ability to predict
how humans will interact with it, the industry can no longer depend
as much on experience and intuition to guide decisions related to
human performance. Instead, a sound scientific basis is necessary
for assessing human performance implications in design, training,
and procedures, just as developing a new wing requires sound aerodynamic
Boeing has addressed
this issue by employing human factors specialists, many of whom are
also pilots or mechanics, since the 1960s. Initially focused on flight
deck design, this group of about 30 experts now considers a much broader
range of elements (see
graphic), such as cognitive psychology, human performance, physiology,
visual perception, ergonomics, and human-computer interface design.
Applied collectively, their knowledge contributes to the design of
Boeing airplanes and support products that help humans perform to
the best of their capability while compensating for their natural
Because improving human performance can help the industry reduce
the commercial aviation accident rate, much of the focus is on designing
human-airplane interfaces and developing procedures for both flight
crews and maintenance technicians. Boeing also continues to examine
human performance throughout the airplane to improve usability,
maintainability, reliability, and comfort. In addition, human factors
specialists participate in analyzing operational safety and developing
methods and tools to help operators better manage human error. These
responsibilities require the specialists to work closely with engineers,
safety experts, test and training pilots, mechanics, and cabin crews
to properly integrate human factors into the design of all Boeing
airplanes. Their areas of responsibility include addressing human
for maintainability and in-service support.
FLIGHT DECK DESIGN
Over the past several decades, safer and more reliable designs have
been responsible for much of the progress made in reducing the accident
rate and increasing efficiency. Improvements in engines, systems,
and structures have all contributed to this achievement. Additionally,
design has always been recognized as a factor in preventing and
mitigating human error. When Boeing initiates a new design activity,
past operational experience, operational objectives, and scientific
knowledge define human factors design requirements. Analytical methods
such as mockup or simulator evaluations are used to assess how well
various design solutions meet these requirements. Underlying this
effort is a human-centered design philosophy that has been validated
by millions of flights and decades of experience. This approach
produces a design that applies technology in the best way to satisfy
- Customer input.
degree of automation.
- Crew interaction
Navigation and Surveillance/Air Traffic Management improvements.
Boeing involves potential customers in defining top-level design
requirements for new designs or major derivatives and in applying
human factors principles. A good example is the high level of airline
involvement in designing the 777. From the beginning, operators’
flight crews and mechanics worked side by side with Boeing design
teams on all airplane systems. Eleven of the initial operators also
participated in dedicated flight deck design reviews early in the
design process. An independent external team of senior human factors
scientists also participated in a parallel set of reviews. In the
final review, flight crews and other representatives from each operator
spent time in the 777 engineering flight simulator to evaluate the
design in a variety of normal and nonnormal situations. These activities
ensured that operator requirements were considered from the beginning,
and validated that the implementation included a sound pilot-flight
degree of automation.
Boeing flight decks are designed to provide automation to assist,
but not replace, the flight crew member responsible for safe operation
of the airplane. Flight crew errors typically occur when the crew
does not perceive a problem and fails to correct the error in time
to prevent the situation from deteriorating. Consequently, Boeing
flight decks incorporate intuitive, easy-to-use systems. These systems
support instrument displays with visual and tactile motion cues
to minimize potential confusion about what functions are automated.
In the fly-by-wire 777, visual and tactile motion cues are provided
by backdriven controls. These controls reinforce situational awareness
and help keep the flight crew fully aware of changes occurring to
the airplane’s status and flight path during all phases of automated
and manual flight.
Flight crew communication relies on the use of audio, visual, and
tactile methods. All these methods must be used appropriately in
the communication that takes place during flight. This includes
crewmember-to-airplane, crewmember-to-crewmember, and airplane-to-crewmember
communication. Consequently, the duplicated flight controls of all
Boeing airplanes are also interconnected. Both control wheels turn
together when either is moved so that the control inputs of each
flight crew member are immediately obvious to the other. The same
is true for column movements. The tactile and visual feedback provided
by interlinkage is much more immediate than verbal coordination
and better enables pilots to help each other in time-critical emergencies.
Navigation and Surveillance/Air Traffic Management interface.
In the future, flight crews will be expected to assume much larger
roles in route planning and metering for approaches. Cognitive engineering
has already assumed an important role as the industry considers
the effects of new technology on the skills, workload, and coordination
with other airplanes required of both flight crews and air traffic
controllers. For example, cooperation among human factors specialists,
data link communications engineers, and end users has resulted in
significant changes in the design of the interfaces that flight
crews and controllers have with the computers that support their
tasks and in the operational use of data link messages. The changes
enhance user comprehension, reduce error rates, and result in decreased
Perhaps the simplest
example is the progression from an aircraft communication addressing
and reporting system interface to a future air navigation system
(FANS) interface for data link. Boeing initially studied the effects
of uplink message formats on pilot comprehension in 747-400 operational
trials (fig. 1).
Lessons learned were used when designing the data link interface
in the Pegasus flight management system incorporated into current-production
757 and 767 airplanes. These same changes are being applied retroactively
to the 747-400. Another example is the 777 communications management
interface, which uses multifunction displays and cursor controls
to simplify management of data-linked communications and can be
customized by operators.
DESIGN FOR MAINTAINABILITY AND IN-SERVICE SUPPORT
Over the past several years, airplane maintenance has benefited
from an increased focus on how human factors can contribute to safety
and operational efficiency. In maintenance, as in flight deck design,
Boeing employs a variety of sources to address human factors issues,
- Chief mechanic
maintainability design tools.
- Fault information
- Customer support
Modeled on the role of chief pilot, a chief mechanic was appointed
to the 777 program and to all subsequent airplane programs (717,
737-600/-700/-800/-900, 757-300, and 767-400 Extended Range [ER]).
As with the chief pilot, the mechanic acts as an advocate for operator
or repair station counterparts. The appointment of a chief mechanic
grew out of the recognition that the maintenance community contributes
significantly to the success of airline operations in both safety
and on-time performance. Drawing on the experience of airline and
production mechanics, reliability and maintainability engineers,
and human factors specialists, the chief mechanic oversees the implementation
of all maintenance-related features.
maintainability design tools.
Beginning with the 777 program, Boeing stopped building full-scale
airplane mockups, which in the past helped determine whether a mechanic
could reach an airplane part for removal and reinstallation. Now,
using a computer-aided three-dimensional interactive application
(CATIA), Boeing makes this type of determination using a human model.
During design of the 737-600/-700/-800/-900, Boeing used human modeling
analysis to determine that the electrical/electronic bay needed
to be redesigned to allow a mechanic to access all wire bundles
for the expanded set of avionics associated with the updated flight
deck concept (fig.
In addition to
ensuring access and visibility, human factors specialists conduct
ergonomic analyses to assess the human capability to perform maintenance
procedures under different circumstances. For example, when a mechanic
needs to turn a valve from an awkward position, it is important
that the force required to turn the valve must be within the mechanic's
capability in that posture. For another example, when a maintenance
operation must be accomplished in poor weather at night, secure
footing and appropriate handling forces are necessary to protect
the mechanic from a fall or from dropping a piece of equipment.
information team (FIT).
Human factors considerations in maintenance also led to the formation
of the FIT. During development of the 737-600/-700/-800/-900, Boeing
chartered the FIT to promote effective presentation of maintenance-related
information, including built-in test equipment (BITE) and maintenance
documentation. The FIT charter has since expanded to promote consistency
in maintenance processes and design across all systems and models.
The goal is to enable mechanics to maintain all Boeing commercial
airplanes as efficiently and accurately as possible. This cross-functional
team has representatives from maintenance, engineering, human factors,
One of the team’s
primary functions is to administer and update standards that promote
uniformity among Boeing airplane maintenance displays. For the text
of these displays, Boeing has created templates that provide for
common fault menus for all systems. The interface should look the
same to the mechanic regardless of the vendor or engineering organization
that designs the component. Engineers responsible for airplane system
design coordinate their BITE and maintenance design efforts with
the FIT. The FIT reviews all information used by the mechanic, including
placards, manuals, training, and size, location, and layout of controls
and indicators, and works with the engineers to develop effective,
consistent displays. The team also provides input and updates to
Boeing design standards and requirements.
In the early 1990s, Boeing formed a maintenance human factors group.
One of the group’s major objectives was to help operators implement
the Maintenance Error Decision Aid (MEDA) process.
The group also
helps maintenance engineers improve their maintenance products,
including Aircraft Maintenance Manuals, fault isolation manuals,
and service bulletins. As maintenance support becomes more electronically
based, human factors considerations have become an integral part
of the Boeing design process for tools such as the Portable Maintenance
Aid. In addition, the group is developing a human factors awareness
training program for Boeing maintenance engineers to help them benefit
from human factors principles and applications in their customer
Failure to follow procedures is not uncommon in incidents and accidents
related to both flight operations and maintenance procedures. However,
the industry lacks insight into why such errors occur. To date,
the industry has not had a systematic and consistent tool for investigating
such incidents. To improve this situation, Boeing has developed
human factors tools to help understand why the errors occur and
develop suggestions for systematic improvements.
the tools operate on the philosophy that when airline personnel
(either flight crews or mechanics) make errors, contributing factors
in the work environment are part of the causal chain. To prevent
such errors in the future, those contributing factors must be identified
and, where possible, eliminated or mitigated. The tools are
Event Analysis Tool.
Error Decision Aid.
Event Analysis Tool (PEAT).
This tool, for which training began in mid-1999, is an analytic
tool created to help the airline industry effectively manage the
risks associated with flight crew procedural deviations. PEAT assumes
that there are reasons why the flight crew member failed to follow
a procedure or made an error and that the error was not intentional.
Based on this assumption, a trained investigator interviews the
flight crew to collect detailed information about the procedural
deviation and the contributing factors associated with it. This
detailed information is then entered into a database for further
analysis. PEAT is the first industry tool to focus on procedurally
related incident investigations in a consistent and structured manner
so that effective remedies can be developed (see
Error Decision Aid (MEDA).
This tool began as an effort to collect more information about maintenance
errors. It developed into a project to provide maintenance organizations
with a standardized process for analyzing contributing factors to
errors and developing possible corrective actions (see "Boeing
Introduces MEDA" in Airliner magazine, April-June 1996,
Factors Process for Reducing Maintenance Errors" in Aero
no. 3, October 1998). MEDA is intended to help airlines shift from
blaming maintenance personnel for making errors to systematically
investigating and understanding contributing causes. As with PEAT,
MEDA is based on the philosophy that errors result from a series
of related factors. In maintenance practices, those factors typically
include misleading or incorrect information, design issues, inadequate
communication, and time pressure. Boeing maintenance human factors
experts worked with industry maintenance personnel to develop the
MEDA process. Once developed, the process was tested with eight
operators under a contract with the U.S. Federal Aviation Administration.
inception of MEDA in 1996, the Boeing maintenance human factors
group has provided on-site implementation support to more than 100
organizations around the world. A variety of operators have witnessed
substantial safety improvements, and some have also experienced
significant economic benefits because of reduced maintenance errors.
Three other tools
that assist in managing error are
- Crew information
- Training aids.
- Improved use
requirements analysis (CIRA).
Boeing developed the CIRA process to better understand how flight
crews use the data and cues they are given. It provides a way to
analyze how crews acquire, interpret, and integrate data into information
upon which to base their actions. CIRA helps Boeing understand how
the crew arrived or failed to arrive at an understanding of events.
Since it was developed in the mid-1990s, CIRA has been applied internally
in safety analyses supporting airplane design, accident and incident
analyses, and research.
Boeing has applied its human factors expertise to help develop training
aids to improve flight safety. An example is the company’s participation
with the aviation industry on a takeoff safety training aid to address
rejected takeoff runway accidents and incidents. Boeing proposed
and led a training tool effort with participation from line pilots
in the industry. The team designed and conducted scientifically
based simulator studies to determine whether the proposed training
aid would be effective in helping crews cope with this safety issue.
Similarly, the controlled flight into terrain training aid resulted
from a joint effort by flight crew training instructor pilots, human
factors engineering, and aerodynamics engineering.
use of automation.
Both human factors scientists and flight crews have reported that
flight crews can become confused about the state of advanced automation,
such as the autopilot, autothrottle, and flight management computer.
This condition is often referred to as decreased mode awareness.
It is a fact not only in aviation but also in today’s computerized
offices, where personal computers sometimes respond to a human input
in an unexpected manner. The Boeing Human Factors organization is
involved in a number of activities to further reduce or eliminate
automation surprises and to ensure more complete mode awareness
by flight crews. The primary approach is to better communicate the
automated system principles, better understand flight crew use of
automated systems, and systematically document skilled flight crew
strategies for using automation. Boeing is conducting these activities
in cooperation with scientists from the U.S. National Aeronautics
and Space Administration (fig.
3). When complete, Boeing will use the results to improve future
designs of the crewmember-automation interface and to make flight
crew training more effective and efficient.
PASSENGER CABIN DESIGN
The passenger cabin represents a significant human factors challenge
related to both passengers and cabin crews. Human factors principles
usually associated with the flight deck are now being applied to
examine human performance functions and ensure that cabin crews
and passengers are able to do what they need or want to do. Some
recent examples illustrate how the passenger cabin can benefit from
human factors expertise applied during design. These include
- Other cabin
The 737-600/-700/-800/-900 is equipped with an improved version
of the overwing emergency exit (fig.
4), which opens automatically when activated by a passenger
or cabin or flight crew member. Human performance and ergonomics
methods played important roles in both its design and testing. Computer
analyses using human models ensured that both large and small people
would be able to operate the exit door without injury. The handle
was redesigned and tested to ensure that anyone could operate the
door using either single or double handgrips. Then, approximately
200 people who were unfamiliar with the design and who had never
operated an overwing exit participated in tests to verify that the
average adult can operate the exit in an emergency. The exit tests
revealed a significantly improved capability to evacuate the airplane.
This major benefit was found to be unique to the 737 configuration.
The human factors methodology applied during test design and data
analysis contributed significantly to refining the door mechanism
design for optimal performance.
Working with payloads designers, human factors specialists also
evaluated cabin crew and passenger reach capability, placard comprehension,
emergency lighting adequacy, and other human performance issues.
Because of the focus on human capabilities and limitations, the
analyses and design recommendations were effective in reducing potential
errors and in increasing usability and satisfaction with Boeing
issues of human usability have also been addressed. For instance,
human factors specialists collaborated with engineers in various
studies during 767-400ER program design. The reach and visibility
of the passenger service units components were reviewed so cabin
crews could use them more easily and effectively. The glare ratio
on the sidewalls was analyzed and improved for increased passenger
comfort. In addition, the cabin crew panel for controlling the in-flight
entertainment system was modified for easier operation and maintainability.
goal of the Boeing design philosophy is to build airplanes that
can be flown safely while offering operational efficiency. An
essential part of this philosophy is continuous improvement
in designs and flight crew training and procedures. Integral
to this effort is an ongoing attempt to better address human
performance concerns as they relate to design, usability, maintainability,
and reliability. By continuously studying the interface between
human performance and commercial airplanes, Boeing continues
to help operators apply the latest human factors knowledge for
increased flight safety.
EVENT ANALYSIS TOOL
Boeing began distributing the Procedural Event Analysis Tool
(PEAT) to its operators. The company is offering this safety
tool to help operators understand the reasons underlying incidents
caused by flight crew deviation from established procedures.
a structured analytic tool (fig.
1) that operators can use to investigate incidents and
develop measures to prevent similar events in the future.
It is available to operators free of charge and is the result
of a cooperative development effort among airlines, pilot
union representatives, and Boeing human factors specialists.
from an extensive effort to identify the key underlying cognitive
factors that contributed to procedural noncompliance in past
accidents. In 1991 Boeing concluded a 10-year study that showed
that flight crew deviation from established procedures contributed
to nearly 50 percent of all hull-loss accidents. The aviation
industry still lacks sufficient knowledge about the reasons
for these deviations, however, and had no formal investigation
tool to help identify them.
addition to helping operators find these reasons, PEAT was
designed to significantly change how incident investigations
are conducted. When followed correctly, the PEAT process focuses
on a cognitive approach (fig.
2) to understand how and why the event occurred, not who
was responsible. Using PEAT successfully depends on acknowledging
the philosophy that flight crews very rarely fail to intentionally
comply with a procedure. In addition, operators must adopt
an investigative approach that fosters cooperation between
the flight crew and the safety officer conducting the investigation.
more than 200 analysis elements that enable the safety officer
to conduct an in-depth investigation, summarize the findings,
and integrate them across various events. PEAT also enables
operators to track their progress in addressing the issues
revealed by the analyses.
can realize several benefits by using PEAT:
- A structured,
systematic approach to investigations.
application and results.
of incident trends and risk areas.
or elimination of procedural-related events.
- A means
for communicating and sharing relevant information between
organizations, both internal and external to the airline.
with existing industry safety tools.
must acquire hands-on training to effectively adopt and apply
the PEAT process and software. Requests for training should
be addressed to Mike Moodi in Boeing Flight Technical Services
(fax 206-662-7812). More information is available on the Boeing
PEAT web site:
HUMAN FACTORS ENGINEERING
BOEING COMMERCIAL AIRPLANES GROUP