HUMAN FACTORS

AVIATION SAFETY

THE ROLE OF

IN IMPROVING

Human error has been documented as a primary contributor

to more than 70 percent of commercial airplane hull-loss

accidents. While typically associated with flight operations,

human error has also recently become a major concern in

maintenance practices and air traffic management. Boeing

human factors professionals work with engineers, pilots,

and mechanics to apply the latest knowledge about the

interface between human performance and commercial

airplanes to help operators improve safety and efficiency

in their daily operations.

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SAFETYCURT GRAEBER

CHIEF ENGINEER

HUMAN FACTORS ENGINEERING

BOEING COMMERCIAL AIRPLANES GROUP

FLIGHT DECK DESIGN

Over the past several decades, saferand more reliable designs have beenresponsible for much of the progressmade in reducing the accident rate andincreasing efficiency. Improvements inengines, systems, and structures haveall contributed to this achievement.Additionally, design has always beenrecognized as a factor in preventingand mitigating human error. WhenBoeing initiates a new design activity,past operational experience, operationalobjectives, and scientific knowledgedefine human factors design require-ments. Analytical methods such asmockup or simulator evaluations areused to assess how well various designsolutions meet these requirements.Underlying this effort is a human-centered design philosophy that hasbeen validated by millions of flightsand decades of experience. Thisapproach produces a design that appliestechnology in the best way to satisfyvalidated requirements:

n Customer input.

n Appropriate degree of automation.

n Crew interaction capability.

n Communication, Navigation and Surveillance/Air

Traffic Managementimprovements.

Customer input. Boeing involvespotential customers in definingtop-level design requirements for newdesigns or major derivatives and inapplying human factors principles. Agood example is the high level of air-line involvement in designing the 777.From the beginning, operators flightcrews and mechanics worked side byside with Boeing design teams on allairplane systems. Eleven of the initialoperators also participated in dedicatedflight deck design reviews early in thedesign process. An independent externalteam of senior human factors scientistsalso participated in a parallel set ofreviews. In the final review, flight crewsand other representatives from eachoperator spent time in the 777 engi-neering flight simulator to evaluatethe design in a variety of normal andnonnormal situations. These activitiesensured that operator requirementswere considered from the beginning,and validated that the implementationincluded a sound pilotflight deckinterface.

Appropriate degree of automation.Boeing flight decks are designed toprovide automation to assist, but notreplace, the flight crew memberresponsible for safe operation of theairplane. Flight crew errors typicallyoccur when the crew does not perceive

a problem and fails to

correct the error in time to preventthe situation from deteriorating.Consequently, Boeing flight decksincorporate intuitive, easy-to-usesystems. These systems support instru-ment displays with visual and tactilemotion cues to minimize potentialconfusion about what functions areautomated. In the fly-by-wire 777,visual and tactile motion cues areprovided by backdriven controls. Thesecontrols reinforce situational awarenessand help keep the flight crew fullyaware of changes occurring to theairplanes status and flight path during all phases of automated andmanual flight.

Crew interaction capability.Flight crew communication relies onthe use of audio, visual, and tactilemethods. All these methods must beused appropriately in the communica-tion that takes place during flight.This includes crewmember-to-airplane,crewmember-to-crewmember, and airplane-to-crewmember communication.Consequently, the duplicated flightcontrols of all Boeing airplanes arealso interconnected. Bothcontrol wheels turntogether

1

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he term human factorshas grown increasinglypopular as the commer-

cial aviation industry has realizedthat human error, rather thanmechanical failure, underlies mostaviation accidents and incidents.If interpreted narrowly,human factors is oftenconsidered synonymouswith crew resourcemanagement (CRM) ormaintenance resourcemanagement (MRM).However, it is muchbroader in both itsknowledge base andscope. Human factorsinvolves gatheringinformation abouthuman abilities, limi-tations, and othercharacteristics andapplying it to tools,machines, systems,tasks, jobs, and envi-ronments to producesafe, comfortable, andeffective human use.In aviation, humanfactors is dedicated tobetter understandinghow humans can mostsafely and efficientlybe integrated with the technology.That understanding is then trans-lated into design, training, policies,or procedures to help humansperform better.

Despite rapid gains in technology,humans are ultimately responsiblefor ensuring the success and safetyof the aviation industry. They mustcontinue to be knowledgeable,flexible, dedicated, and efficientwhile exercising good judgment.Meanwhile, the industry continuesto make major investments intraining, equipment, and systemsthat have long-term implications.

Because technology continues toevolve faster than the ability topredict how humans will interactwith it, the industry can no longerdepend as much on experienceand intuition to guide decisionsrelated to human performance.

Instead, a sound scientific basisis necessary for assessing humanperformance implications in design,training, and procedures, just asdeveloping a new wing requiressound aerodynamic engineering.

Boeing has addressed this issueby employing human factors specialists, many of whom are alsopilots or mechanics, since the1960s. Initially focused on flightdeck design, this group of about30 experts now considers a muchbroader range of elements (seegraphic), such as cognitive psychology, human performance,

physiology, visual perception,ergonomics, and human-computerinterface design. Applied collec-tively, their knowledge contributesto the design of Boeing airplanesand support products that helphumans perform to the best of

their capability whilecompensating for theirnatural limitations. Because improving

human performance canhelp the industry reducethe commercial aviationaccident rate, much ofthe focus is on design-ing human-airplaneinterfaces and develop-ing procedures for bothflight crews and main-tenance technicians.Boeing also continuesto examine human performance throughoutthe airplane to improveusability, maintainability,reliability, and comfort.In addition, humanfactors specialists participate in analyzingoperational safety anddeveloping methods andtools to help operatorsbetter manage human

error. These responsibilities requirethe specialists to work closely withengineers, safety experts, test andtraining pilots, mechanics, andcabin crews to properly integratehuman factors into the design ofall Boeing airplanes. Their areasof responsibility include address-ing human factors in

1. Flight deck design.

2. Design for maintainability and in-service support.

3. Error management.

4. Passenger cabin design.

T

Humanperformance

Cognitivehumanfactors

Physicalhumanfactors

Industrialdesign

User-centereddesign

Humanbehavior

Humandimensions

n Population type - sex, race, profession

n Protective equipment -gloves, clothing

n Range in population - percentilesn Work envelope - reach, vision,

access capabilities/limits

n Biomechanics - structure, posturen Operating environment -

temperature, vibration, noise, jet lag

n Behavioral - habits, stress, danger, emotion, group dynamics

n Cognitive - decisionmaking, learning ability, perception, knowledge,interpretation, reasoning, memory

n Cultural - expectations, language, education, customs

n Environmental - space, shape, lighting, texture, color, hazards, noise

n Performance - strength, endurance, speed, reaction

n Sensory input - vision, smell, touch

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when either is moved so that the con-trol inputs of each flight crew memberare immediately obvious to the other.The same is true for column move-ments. The tactile and visual feedbackprovided by interlinkage is much moreimmediate than verbal coordinationand better enables pilots to help eachother in time-critical emergencies.

Communication, Navigation and Surveillance/Air TrafficManagement interface. In the future, flight crews will beexpected to assume much larger rolesin route planning and metering forapproaches. Cognitive engineering hasalready assumed an important role asthe industry considers the effects ofnew technology on the skills, work-load, and coordination with otherairplanes required of both flightcrews and air trafficcontrollers. For example,cooperation among humanfactors specialists, data linkcommunications engineers, andend users hasresulted in sig-nificant changes inthe design of theinterfaces that flightcrews and controllershave with the computersthat support their tasksand in the operationaluse of data link messages.The changes enhance usercomprehension, reduce errorrates, and result in decreasedtraining requirements.

Perhaps the simplest example is theprogression from an aircraft communi-cation addressing and reporting systeminterface to a future air navigationsystem (FANS) interface for data link.Boeing initially studied the effects of uplink message formats on pilotcomprehension in 747-400 operationaltrials (fig. 1). Lessons learned wereused when designing the data linkinterface in the Pegasus flight man-agement system incorporated intocurrent-production 757 and 767 air-planes. These same changes are beingapplied retroactively to the 747-400.Another example is the 777 commu-nications management interface,which uses multifunction displays andcursor controls to simplify managementof data-linked communications andcan be customized by operators.

DESIGN FOR MAINTAINABILITYAND IN-SERVICE SUPPORT

Over the past several years, airplanemaintenance has benefited from anincreased focus on how human factorscan contribute to safety and opera-tional efficiency. In maintenance, as inflight deck design, Boeing employs avariety of sources to address humanfactors issues, including

n Chief mechanic participation.

n Computer-based maintainabilitydesign tools.

n Fault information team.

n Customer support processes.

Chief mechanic participation. Modeled on the role of chief pilot, achief mechanic was appointed to the777 program and to all subsequentairplane programs (717, 737-600/-700/-800/-900, 757-300, and 767-400Extended Range [ER]). As with thechief pilot, the mechanic acts as anadvocate for operator or repair stationcounterparts. The appointment of achief mechanic grew out of therecognition that the maintenancecommunity contributes significantlyto the success of airline operations inboth safety and on-time performance.Drawing on the experience of airlineand production mechanics, reliabilityand maintainability engineers, and

human factors specialists, the chiefmechanic oversees the implementationof all maintenance-related features.

Computer-based maintainability design tools.Beginning with the 777 program, Boeingstopped building full-scale airplanemockups, which in the past helpeddetermine whether a mechanic couldreach an airplane part for removal andreinstallation. Now, using a computer-aided three-dimensional interactiveapplication (CATIA), Boeing makes thistype of determination using a humanmodel. During design of the 737-600/-700/-800/-900, Boeing used humanmodeling analysis to determine thatthe electrical/electronic bay needed tobe redesigned to allow a mechanic toaccess all wire bundles for the expandedset of avionics associated with theupdated flight deck concept (fig. 2).In addition to ensuring access andvisibility, human factors specialistsconduct ergonomic analyses to assessthe human capability to perform main-tenance procedures under differentcircumstances. For example, when amechanic needs to turn a valve froman awkward position, it is importantthat the force required to turn thevalve must be within the mechanic'scapability in that posture. For anotherexample, when a maintenance operationmust be accomplished in poor weatherat night, secure footing and appropriatehandling forces are necessary to pro-tect the mechanic from a fall or fromdropping a piece of equipment.

Fault information team (FIT).Human factors considerations in main-tenance also led to the formation ofthe FIT. During development of the737-600/-700/-800/-900, Boeingchartered the FIT to promote effectivepresentation of maintenance-relatedinformation, including built-in testequipment (BITE) and maintenancedocumentation. The FIT charter hassince expanded to promote consistencyin maintenance processes and designacross all systems and models. Thegoal is to enable mechanics to main-tain all Boeing commercial airplanesas efficiently and accurately as possi-ble. This cross-functional team has

representatives from maintenance, engi-neering, human factors, and operators.

One of the teams primary functionsis to administer and update standardsthat promote uniformity among Boeingairplane maintenance displays. Forthe text of these displays, Boeing hascreated templates that provide forcommon fault menus for all systems.The interface should look the same tothe mechanic regardless of the vendoror engineering organization thatdesigns the component. Engineersresponsible for airplane system designcoordinate their BITE and maintenancedesign efforts with the FIT. The FITreviews all information used by themechanic, including placards, manuals,training, and size, location, and layoutof controls and indicators, and workswith the engineers to develop effective,consistent displays. The team alsoprovides input and updates to Boeingdesign standards and requirements.

Customer support processes.In the early 1990s, Boeing formed amaintenance human factors group.One of the groups major objectiveswas to help operators implement theMaintenance Error Decision Aid (MEDA) process.

The group also helps maintenanceengineers improve their maintenance products, including Aircraft MaintenanceManuals, fault isolation manuals, andservice bulletins. As maintenancesupport becomes more electronicallybased, human factors considerationshave become an integral part of theBoeing design process for tools suchas the Portable Maintenance Aid. Inaddition, the group is developing ahuman factors awareness training pro-gram for Boeing maintenance engineersto help them benefit from humanfactors principles and applications intheir customer support work.

ERROR MANAGEMENT

Failure to follow procedures is notuncommon in incidents and accidentsrelated to both flight operations andmaintenance procedures. However, theindustry lacks insight into why sucherrors occur. To date, the industry has

not had a systematic and consistenttool for investigating such incidents.To improve this situation, Boeing hasdeveloped human factors tools to helpunderstand why the errors occur anddevelop suggestions for systematicimprovements.

Two of the tools operate on the phi-losophy that when airline personnel(either flight crews or mechanics) makeerrors, contributing factors in the workenvironment are part of the causalchain. To prevent such errors in thefuture, those contributing factors mustbe identified and, where possible,eliminated or mitigated. The tools are

n Procedural Event Analysis Tool.

n Maintenance Error Decision Aid.

Procedural Event Analysis Tool (PEAT). This tool, for which training began inmid-1999, is an analytic tool createdto help the airline industry effectivelymanage the risks associated withflight crew procedural deviations. PEATassumes that there are reasons whythe flight crew member failed to followa procedure or made an error and thatthe error was not intentional. Basedon this assumption, a trained investi-gator interviews the flight crew tocollect detailed information about theprocedural deviation and the con-tributing factors associated with it.This detailed information is thenentered into a database for furtheranalysis. PEAT is the first industrytool to focus on procedurally relatedincident investigations in a consistent

UPLINK MESSAGE FORMAT1FIGURE

CATIA HUMAN MODELING2FIGURE

2

3

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and structured manner so that effectiveremedies can be developed (see p. 31).

Maintenance Error Decision Aid (MEDA). This tool began as an effort to collectmore information about maintenanceerrors. It developed into a project toprovide maintenance organizations witha standardized process for analyzingcontributing factors to errors anddeveloping possible corrective actions(see Boeing Introduces MEDA inAirliner magazine, AprilJune 1996, andHuman Factors Process for ReducingMaintenance Errors in Aero no. 3,October 1998). MEDA is intended tohelp airlines shift from blaming main-tenance personnel for making errorsto systematically investigating andunderstanding contributing causes. As with PEAT, MEDA is based on thephilosophy that errors result from aseries of related factors. In maintenancepractices, those factors typically includemisleading or incorrect information,design issues, inadequate communica-tion, and time pressure. Boeing main-tenance human factors experts workedwith industry maintenance personnelto develop the MEDA process. Oncedeveloped, the process was tested witheight operators under a contract withthe U.S. Federal Aviation Administration.

Since the inception of MEDA in1996, the Boeing maintenance humanfactors group has provided on-siteimplementation support to more than100 organizations around the world.A variety of operators have witnessedsubstantial safety improvements, andsome have also experienced significanteconomic benefits because of reducedmaintenance errors.

Three other tools that assist inmanaging error are

n Crew information requirementsanalysis.

n Training aids.

n Improved use of automation.

Crew information requirements analysis (CIRA). Boeing developed the CIRA process tobetter understand how flight crewsuse the data and cues they are given.It provides a way to analyze how

crews acquire, interpret, and integratedata into information upon which tobase their actions. CIRA helps Boeingunderstand how the crew arrived orfailed to arrive at an understanding ofevents. Since it was developed in themid-1990s, CIRA has been appliedinternally in safety analyses supportingairplane design, accident and incidentanalyses, and research.

Training aids. Boeing has applied its human factorsexpertise to help develop training aidsto improve flight safety. An example isthe companys participation with theaviation industry on a takeoff safetytraining aid to address rejected takeoffrunway accidents and incidents.Boeing proposed and led a training

tool effort with participation from linepilots in the industry. The teamdesigned and conducted scientificallybased simulator studies to determinewhether the proposed training aidwould be effective in helping crewscope with this safety issue. Similarly,the controlled flight into terraintraining aid resulted from a jointeffort by flight crew training instructorpilots, human factors engineering,and aerodynamics engineering.

Improved use of automation. Both human factors scientists andflight crews have reported that flightcrews can become confused about thestate of advanced automation, such asthe autopilot, autothrottle, and flightmanagement computer. This condition

is often referred to as decreased modeawareness. It is a fact not only in avi-ation but also in todays computerizedoffices, where personal computerssometimes respond to a human inputin an unexpected manner. The BoeingHuman Factors organization is involvedin a number of activities to furtherreduce or eliminate automation sur-prises and to ensure more completemode awareness by flight crews. Theprimary approach is to better commu-nicate the automated system principles,better understand flight crew use ofautomated systems, and systematicallydocument skilled flight crew strategiesfor using automation. Boeing is con-ducting these activities in cooperationwith scientists from the U.S. NationalAeronautics and Space Administration(fig. 3). When complete, Boeing willuse the results to improve futuredesigns of the crewmember-automationinterface and to make flight crewtraining more effective and efficient.

PASSENGER CABIN DESIGN

The passenger cabin represents a sig-nificant human factors challenge relatedto both passengers and cabin crews.Human factors principles usually

associated with the flight deck arenow being applied to examine humanperformance functions and ensure thatcabin crews and passengers are able todo what they need or want to do.Some recent examples illustrate howthe passenger cabin can benefit fromhuman factors expertise applied duringdesign. These include

n Automatic overwing exit.

n Other cabin applications.

Automatic overwing exit. The 737-600/-700/-800/-900 isequipped with an improved version ofthe overwing emergency exit (fig. 4),which opens automatically when acti-vated by a passenger or cabin or flightcrew member. Human performance andergonomics methods played importantroles in both its design and testing.Computer analyses using human modelsensured that both large and smallpeople would be able to operate the exit door without injury. The handlewas redesigned and tested to ensurethat anyone could operate the doorusing either single or double handgrips.Then, approximately 200 people whowere unfamiliar with the design andwho had never operated an overwingexit participated in tests to verify

that the average adult can operate theexit in an emergency. The exit testsrevealed a significantly improved capa-bility to evacuate the airplane. Thismajor benefit was found to be uniqueto the 737 configuration. The humanfactors methodology applied during testdesign and data analysis contributedsignificantly to refining the door mech-anism design for optimal performance.

Other cabin applications.Working with payloads designers, humanfactors specialists also evaluate cabincrew and passenger reach capability,placard comprehension, emergencylighting adequacy, and other humanperformance issues. Because of the focuson human capabilities and limitations,the analyses and design recommenda-tions are effective in reducing potentialerrors and in increasing usability andsatisfaction with Boeing products.

More general issues of human usabilityhave also been addressed. For instance,human factors specialists collaboratedwith engineers in various studies dur-ing 767-400ER program design. Thereach and visibility of the passengerservice units components werereviewed so cabin crews could usethem more easily and effectively. Theglare ratio on the sidewalls was ana-lyzed and improved for increased pas-senger comfort. In addition, the cabincrew panel for controlling the in-flightentertainment system was modified foreasier operation and maintainability.

The overwing exit and the exit placardwere redesigned using human factorsmethodology.

737-600/-700/-800/-900OVERWING EMERGENCY EXIT4

FIGURE

4

Human factors specialists use an eyetracker to study pilot mode aware-ness in the 747-400 flight deck.

FLIGHT CREW HUMAN FACTORS STUDY3

FIGURE

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very rarely fail to intentionally comply with a procedure.In addition, operators must adopt an investigativeapproach that fosters cooperation between the flightcrew and the safety officer conducting the investigation.

PEAT contains more than 200 analysis elements thatenable the safety officer to conduct an in-depth investigation, summarize the findings, and integratethem across various events. PEAT also enables operatorsto track their progress in addressing the issues revealedby the analyses.

Operators can realize several benefits byusing PEAT: n A structured, systematic approach

to investigations.n Consistent application and results.n Visibility of incident trends and

risk areas.n Reduction or elimination of

procedural-related events.n Improved operational safety. n Improved economic efficiencies.n A means for communicating and

sharing relevant information betweenorganizations, both internal and external to the airline.

n Compatibility with existing industry safety tools.

Operators must acquire hands-on trainingto effectively adopt and apply the PEAT process andsoftware. Requests for training should be addressed to Mike Moodi in Boeing Flight Technical Services (fax 206-662-7812). More information is available on theBoeing PEAT web site:

http://www.boeing.com/news/techissues/peat/

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PROCEDURAL EVENT ANALYSIS TOOL

A chief goal of the Boeing design philosophyis to build airplanes that can be flown

safely while offering operational efficiency. An essential partof this philosophy is continuous improvement in designs andflight crew training and procedures. Integral to this effort isan ongoing attempt to better address human performance con-cerns as they relate to design, usability, maintainability, andreliability. By continuously studying the interface betweenhuman performance and commercial airplanes, Boeing continuesto help operators apply the latest human factors knowledge forincreased flight safety.

S U M M A R Y

In mid-1999 Boeing began distributing the Procedural EventAnalysis Tool (PEAT) to its operators. The company is offeringthis safety tool to help operators understand the reasonsunderlying incidents caused by flight crew deviation fromestablished procedures.

PEAT is a structured analytic tool (fig. 1) that operators canuse to investigate incidents and develop measures to preventsimilar events in the future. It is available to operators freeof charge and is the result of a cooperative developmenteffort among airlines, pilot union representatives, and Boeinghuman factors specialists.

PEAT originated from an extensive effort to identify thekey underlying cognitive factors that contributed to proce-dural noncompliance in past accidents. In 1991 Boeingconcluded a 10-year study that showed that flight crewdeviation from established procedures contributed to nearly50 percent of all hull-loss accidents. The aviation industrystill lacks sufficient knowledge about the reasons for thesedeviations, however, and hadno formal investigation tool tohelp identify them.

In addition to helping opera-tors find these reasons, PEATwas designed to significantlychange how incident investi-gations are conducted. When followed correctly, the PEATprocess focuses on a cognitiveapproach (fig. 2) to understandhow and why the eventoccurred, not who was respon-sible. Using PEAT successfullydepends on acknowledging thephilosophy that flight crews

Yes

Operations report (FOQA) Crew report

(BASIS/ASIS, ASAP)

Collect event

description

Identify procedural

errors

Analyze contributing

factors

Develop recommend-ations/share

with crew

Airline implements

enhancements

Monitorsafety

performance

Enter into PEAT database

Analyze data and trends

Share data:n Internaln External (voluntary)

PEAT?

Explain PEAT purpose and philosophy

Collect general

information

THE PEAT PROCESS1FIGURE

Crew short-term sensory store

Contributing factors:n Proceduraln Environmental/

facilitiesn Equipmentn Situation awarenessn Crew performance

shapingn Crew coordination

and communicationn Technical knowledge,

skills, and experiencen Others

Long-term memory

Working memory

Crew response execution

Crew decision and response

selection

Stimuli

Memory

Crew actions

Feedback

Crew perception

Crew attention resources

TAKING A COGNITIVE APPROACH2FIGURE

BOEING POSITION ON NONPUNITIVE REPORTING

Improving the safety of flight operations depends onunderstanding the lessons learned from operationalevents. Success depends on having sufficient data todo so. Today the industrys data scope is limitedbecause the only data guaranteed to be collected isthat related to accidents and major incidents. Amore proactive approach is needed if we are tomove forward.

Unfortunately, it is difficult to obtain insightfuldata in an aviation system that focuses on account-ability. Flight and maintenance crews are oftenunduly exposed to blame because they are the lastline of defense when unsafe conditions arise. Wemust overcome this "blame" culture and encourageall members of our operations to be forthcoming

after any incident. We must be careful not to limitdata collection to any one segment of the safetychain. Boeing believes that if we, the aviation com-munity, hope to further reduce the overall accidentrate, we must continue to promote and implementproactive, nonpunitive safety reporting programsdesigned to collect and analyze aviation safetyinformation.

CHARLES R. HIGGINS J . KENNETH HIGGINS

VICE PRESIDENT, AVIATION VICE PRESIDENT, AIRPLANE SAFETY AND AIRWORTHINESS VALIDATION AND FLIGHT OPERATIONS

BOEING COMMERCIAL BOEING COMMERCIALAIRPLANES GROUP AIRPLANES GROUP