aircraft_seats

8/7/2019 aircraft_seats

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University of Sheffield

Department of Mechanical Engineering

Human Factors Case Study

AIRCRAFT SEATS

Michelle Hirlam

April 2002


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Introduction and BackgroundIntroduction and Background

This case study examines the ergonomics / human factors issuesregarding civilian passenger aircraft seats.

Seats are the most critical component within the aircraft cabin interioras 90-95% of a passenger's flying time is spent in his/her seat.

History of Seat Design Philosophy

1930s 1980s 2000s

1930s - 40s

EARLY COMMERCIAL

PASSENGER AIRCRAFT-FEW SEATS , SPACIOUS &

LUXURIOUS FOR ALL

PASSENGERS

1960s - 1990s AIR TRAVEL

FOR THE MASSES. BOEING

INTRODUCE POPULAR 737IN 1968. - MINIMAL SPACE

BETWEEN SEATS TO FIT AS

MANY PASSENGERS AS

POSSIBLE. INTRODUCTION

OF ECONOMY CLASS

SEATS.

TODAY TREND BACK

TOWARDS GIVING

PASSENGERS MOREROOM - AIRLINES ARE

REMOVING SEATS FROM

THEIR CABINS TO

SATISFY AND WIN

CUSTOMERS


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Key Design IssuesKey Design Issues

Two main areas of design influenced by Human Factors:

COMFORT AND HEALTH & SAFETY

The comfort of the passenger is

extremely important for all journeys,but especially on long-haul flightswhich may be up to 16 hours long.

The safety of all passengers mustbe paramount. Quick and easy exitfrom the cabin must be assured inan emergency evacuation.

Health problems related to air travel:

Low back pain

Joint stiffness

Deep Vein Thrombosis

(not proven link)

HEADREST -CORRECT HEIGHT& ANGLE

CORRECT SEATWIDTH

SUFFICIENT LEGROOM

COMFORTABLE

POSTURE -LUMBERSUPPORT

SEAT RECLINE

FOOTREST -ADJUSTABLE /

CORRECT ANGLE& DISTANCEFROM SEAT

ARMREST -CORRECT HEIGHT /WIDTH, &MATERIAL

UPHOLSTERY -THERMALCOMFORT

Overall comfort is dependent on many factors - most are related to how well the seat matches

the physical dimensions of the passenger.


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To design in terms of user comfort

a knowledge ofANTHROPOMETRICS is required.

Key Design IssuesKey Design Issues -- AnthropometricsAnthropometrics

Aircraft seats are generally designed for 5%ile female to 95%ile male. The .population the

data is taken from depends largely on the routes the aircraft is .intended to fly - Co-

determinants of anthropometry being ethnic origin, geographic region, socio-economic status,

and health.

A populations anthropometric data alters over time, this is an important issue as .many of

todays aircraft have been in service for over a decade, and were often designed using out of

date data.

Increasing percentage of elderly population- dimensions can change considerably in .terms

of stature. Weight gain in later life is also very common, especially among women.

Many of the issues which affect the comfort of the passenger are directly related to.the

correct sizing of the seat. It is therefore crucial to use the anthropometrical data .relating

to the target users.

SOME KEY HUMAN DIMENSIONS

Knee to buttock length Sitting height

Shoulder width Knee to ankle height

Thigh width Shoulder to elbow height


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Anthropometrics ResearchAnthropometrics Research

imension

(Minimum unless otherwise stated)

Seat cushion height (floor to front seat edge)* 410 410 380 305 356

Seat cushion width 460 400 483

Seat cushion width between armrest 460 460 457

Seat cushion width including armrest 565

Seat cushion length 400 410 432 470

Armrest height above compressed seat 230

Armrest height above uncompressed seat 165 200 190.5

Armrest width 60 50

Backrest height 710

Backrest width 520

Backrest length (seat pan to top edge) 600

Aisle width to height of 635mm 380(508+)

Edwards &

Edwards (1990)

Cumberland and

Bowey (1950)

McClelland

(1986)

Stern

(1988)

Guidelines given for aircraft seat dimensions in previous research and publications based on anthropometric data. Taken from Joint Aviation Authorities Review. [8]

A study has also been made in to the optimum seat depth. It highlights that the relatively large seat depths of

aeroplane seats contribute to the feelings of discomfort when sitting for long periods of time.

[6 ]

It is important that research is based on the most up-to-date and relevant anthropometric data

as different populations have different characteristics.

Research into appropriate dimensions for aircraft seats has been carried out in the past based

on anthropometric data available at the time. [8]


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A well designed chair should: [7,18]

Provide support for your back so it can .maintain

its natural lordotic curve.

Give you the freedom to change your position easily

and often without the loss of comfort or support.

Distribute your weight evenly.

Key Design IssuesKey Design Issues Postural ComfortPostural ComfortSitting posture is directly related to comfort. Ourbodies, particularly our spines, were not designed tosit in chairs for hours on end.

Sitting causes straightening of the natural curvature ofthe spine which results in a constant strain onvertebral discs and the the back muscles. Sitting in arelaxed way causes 35% greater stress on our discsthan when we stand. [7,18,22]

Prolonged sitting results in muscle fatigue, stiffness

causes of discomfort.To try to alleviate this problem, seats should beshaped to offer lumber support, ideally this should beadjustable.

Also the curvature of the lumber region becomes morelordotic as a person reclines, therefore seat spacingshould allow for extensive seat recline.

As sitting has been shown to put very largestrains on the back, when designing anaircraft seat in which passengers will be satfor extended periods of time, it is importantthat the research on best sitting postures beutilised to minimise the stress in the back asmuch as possible.


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Key Design IssuesKey Design Issues ComfortComfort OverviewOverview

PUBLISHED HUMAN FACTORS DESIGNRECOMMENDATIONS FORCOMFORTABLE AIRPLANE SEATS.[23]

A 5 degree seat-pan pitch with a 105 degree.seat-to-back rest angle for normal upright

.position.A 45 degree seat recline over a continuous.range.

A backrest height of 24 inches to the base of.the headrest.

A minimum seat-width clearance of 19.inches between armrests.

A seat-pan that automatically adjusts to a

.horizontal position as the backrest is reclined.Separate 2 inch-wide armrests for side-by-.side passengers or one 5.25 inch armrest to.be shared by the passengers.

A seat clearance of 12-13 inches to provide.ample leg space.


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Key Design IssuesKey Design Issues Health & SafetyHealth & Safety

Passengers must be able to exit seat safely in

.the case of an emergency evacuation.(Figure shows potential tripping hazard of foot supports)

Passengers must be able to adopt the brace

.position in the event of an emergency landing.(Figure shows recommended crash brace position CAA 1995)

DEEP VEIN THROMBOSIS (DVT)

DVT is a condition in which blood clots form in the deepveins, usually of the leg. It is associated with : reduction inblood flow, changes in blood viscosity and damage of thevein wall.

While there is only circumstantial evidence to suggest acausation link between prolonged sitting in aircraft and theoccurrence of DVT it is recommended that sufficientlegroom be provided to allow movement (stretching) andchanges in posture throughout the journey, and thatpossible benefits may be gained by wearing supportstockings. However it is generally thought that DVT occursmost commonly in those people who have an existingdisposition to blood clots before they fly. [3 11,16]


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Other IssuesOther Issues

Location of reading light

To illuminate reading material avoiding eye strain but not disturb . .

other passengers.

Height of seat backs[5]

To avoid feelings of claustrophobia.

Location of life jacket[5]

Easily accessible, yet positioned discretely out of direct sight.

Location of entertainment consol

Should be in correct field of vision

seat back locations better than overhead

screens.


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Current StandardsCurrent Standards

Currently Civil Aviation Authority is the only regulatory body to proscribe minimum space forseated passengers. - C.A.A.Airworthiness Notice 64 (AN64)[9]

Applies only to British registered aircraft over 5700kg MTWA which carry 20 passengers ormore. Took effect in 1989.

The standard is concerned only with the safety aspects of ingress and egress from the seat,in terms of the space available to the passenger to do this.

- Specifies that a fully loaded aircraft must be evacuated within and 90sec.

Defines 3 critical dimensions

based on anthropometric data for 5th

%ile female to 95th

%ile male population. aimed at minimising the effects of low seat pitches on the comfort of the seat and the . . .. ease of egress from the seats.

Does not define minimum foot room - a foot clearance envelope

i.e. room for feet to ensure health sitting posture and to avoid seat structures when . . . . . . .. accessing/exiting the seats.

The standards for aircraft seats, the FAR Section 25.853 and the JAR25.785[10] outlinecriteria for the design of aircraft seats in terms of structural integrity and safety. They donot however specify any features of the seat to ensure passenger comfort.


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AN64AN64 Critical Minimum DimensionsCritical Minimum Dimensions

Dimension Description Minimum

A Minimum distance between the back support cushion of a seat and the back

of the seat or other fixed structure in front of the seat.

660mm

(26 inches)

B The minimum distance between a seat and the seat or other fixed structure

in front.

17 mm

(7inches)

C The minimum vertically projected distance between seat rows or between a

seat and any fixed structure forward of the seat.

76mm

(3inches)

Defines 3 critical dimensions

Based on anthropometric data for 5th % ile female. to 95th % ile male population.

Aimed at minimising the effects of low seat .pitches on the ability of passengers to fit into theseats, and on the ease of egress from the seats.

There are no specific standards relating to designing seatingto ensure passenger comfort, however a seat which fits wella passengers bodily dimensions will generally ensure a baselevel of comfort.


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Review of AN64Review of AN64In 2001 the Joint Aviation Authorities conducted a review of the minimum

dimensions stated in the AN64 with relevance to todays population.[8]

Objective of the review was to evaluate both the scope of the AN64 and the

minimum dimensional values stated in it.

Why was a review needed?

Generally increasing body dimensions within European and US populations.Secular growth of population. Average secular increase in statue in the order of 10mm per..decade in Europe and N.America.[7] Western populations are also showing an increase in

.breadth an estimated 22% of US population are obese. [14]

Increase in the number of Third Agers (55+ years of age).

It is predicted that by 2020 there will be as many old people as there are

.younger ones. The size and abilities of adults changes as they age.

Increasing number of long duration flights.

Sitting comfort is highly dependent on the length of time in the sitting posture.

High density seating.

As airlines more for more seats on each flight, passenger space is compromised.

As with the CAAs AN64, the JAA report was concerned only with the safety of passengers, butin addition to the AN64, considers the safety aspects of brace position, and health problemsassociated with prolonged sitting.


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J.A.A. ConclusionsJ.A.A. Conclusions

Where safety is concerned the critical dimensions should be increased to cover the 1st%ile to 99th%ilerange. This will also anticipate gradual future growth of population.

Current requirements for dimension A will only accommodate up to 77th%ile of Europeanpopulation. Dimensions B and C, even fewer passengers

Dimension A should be increased to 28.2 (for up to 95th % ile European passenger). Ideally dimension Ashould be 29.4 (for up to 99th%ile world)

Dimension A should be measured with the seat in front in the fully reclined position, current AN64requirements measure all seats in upright position.

Dimension B was found to be unacceptable for both larger and smaller passengers. Recommendedminimum at armrest level of 9-10 and 8.3 at seat cushion level.

Dimension C would need to be increased from 3 to 12 to allow a 95th%ile passenger to standupright

between rows of seats.

Minimum dimensions for the depth and width of the seat together with the armrest should bespecified as these are important for seat access and spacing issues.

Seat dimensions should allow for use by older passengers as the proportion of older people in thepopulation is growing significantly.


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Application ofKey IssuesApplication ofKey Issues

The extent to which the human factors issues have beenintegrated into the design of aircraft seats is largely

dependent on the type of seat.

Seat pitch in Business Class is on average 75 % more than in Economy

Class, across major airlines.[20]

Seat pitch in First Class is on average 260 % more than in Economy Class,

across major airlines.[20]

Smaller commuter aircraft (50-70 seats) traditionally have smaller seats.

- Due to the shorter flight times, these aircraft are generally less comfortable

. as seats have less recline, less support and less adjustability.

Seats broadly fall in to two categories:

ECONOMY CLASS or BUSINESS / FIRST CLASS


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Economy SeatsEconomy Seats

Limited leg room low seat

pitch.

Narrow seats.

Narrow armrests.

N

o footrests.Headrests poorly positioned, .

fixed.

Limited recline.

Lack good lower back support

to lumber region.

N

ot enough room to open alaptop computer.

Seat support legs can causepassengers to place their feet inthe aisle, posing a trippinghazard.


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Business/First Class SeatsBusiness/First Class Seats

Ample leg room.

Wider seats.

Room for laptop .

.computer.

6ft Fully flat beds.

Adjustable footrests.

Adjustable headrests.

Wide armrests.

Improved lumber support.

Can apply pressure to the back of calf. during sleep.


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ConclusionsConclusions

Trend going into 21st century is the upgrading of economy classsections by the removal of seats to increase seat pitch.

Consumer pressure is starting to force airlines into giving humanfactors issues higher priority in the budget / economy sector.

While business and first class seating has always been of a muchhigher standard than economy class, and has incorporated manyergonomic / human factors features in its design, airlines are now

competing with even more new features. Fully flat beds beingquite a recent introduction on some aircraft.

Seats have exacting standards for strengths, weight, and fire resistance[10], but only in the UK for issues . ..relating to the allowable space given to passengers between the seats.

There are no specific standards pertaining to comfort.

Aircraft cabin interiors are not generally designed with human factors uppermost, particularly economy class.

Economy class seating design is dominated by economics seats and spaces between them are of.minimum size to allow maximum number of passengers.

Business and First Class seating places greater emphasis on ergonomic / human factors features.

American Airlines is increasing the seat pitch for all of its economy class seats across its entire fleet. Also fitting new seatswith six way adjustable headrests and power port access and telephones in every row.[19] Other major airlines with doubtless

be quick to follow as customersare increasingly choosing airlines based on the quality of their economy class seating


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ReferencesReferences

Journal & Newspaper Articles

[1]Barkla, D. The estimation of Body Measurements ofBritish Population in relation to Seat Design. Ergonomics.4, p123-232. 1961

[2]Closing the Comfort Gap Paul Sillers BusinessAviation & Regional Transport, May 1992

[3] Burnand, K., Smith, A. Air travel and Deep VeinThrombosis The London Experience. CardiovasularSurgery. 9(2) p146-147(2001)

[4]Call for Airlines to Think Bigger Frary M.

The Times Newspaper Issue: February 21, 2001

[5]Cumberland, C.H., Bowey, G.S. Passenger Seats for

Aircraft : A survey of the considerations to be borne inmind in designing furniture for maximum safety andcomfort. Aircraft Engineering. XXII (259) p250-255.(1950)

[6]Goonetilleke, R.S., Feizhou, S. A Methodology toDetermine the Optimum Seat Depth. International Journalof Industrial Ergonomics. 27 p207-217 (2001)

[7] Vergara,M., Page,A. Relationship Between Comfortand Back Posture and Mobility in Sitting-Posture. AppliedErgonomics. 33 p1-8. 2002

Standards and Institute Reports.

[8]Anthropometric Study to Update Minimum AircraftSeating Standards. Prepared for Joint Aviation Authorities.July 2001.

www.ice.co.uk/transport/CAA/Passenger%20seat%20space.pdf

[9]Civil Aviation Authority Airworthiness Notice No.64

www.srg.caa.co.uk/publications/cap455_airworthiness_notices.pdf

[10] JAR 25.785. Aviation Regulation for Large Aircraft.Joint Aviation Authorities.

www.jaa.nl/jar/jar/355000/355303/355303.pdf

[11] Travellers Thrombosis- Review of DVT Associatedwith Travel. Aerospace Medical Association- AirTransport Medicine Committee. April 2001


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ReferencesReferences

Websites

[12]Back Care on Airplanes. Dr.Hedgewww.spineuniverse.com/index.html?http&&&www.spineuniverse.com/work/proergo/ergo101sit.htm

[13] Balanced sitting posture on forward slopingseat.A.C.Mandal. Copenhagenhttp://w1.1585.telia.com/~u139600392/

[14] CNN Website.www.cnn.com/HEALTH/9805/28/obesity/

[15]Continental aircraft accessibility-moveable arm rests.http://www.continental.com/dash/build_dash.asp?tis_01_05_03_05

[16]DVT to Shape Aircraft Seat Design 18th

Sept. 2001http://news.bbc.co.uk/hi/english/uk/wales/newsid_1549000/1549458.stm

[17]Goodrich and NuBax introduce improved airlineseating 21 June 2001http://defence-data.com/paris2001/pagepa1096.htm

[18] Investigation of Spinal Curvature While ChangingOnes Posture During Sitting. Faiks,F., Reineche, S.

http://www.bankandoffice.com/knowledge/spinecurve.htm

[19]Skytrax-The world Airline Site. American airlineseats.http://www.airlinequality.com/main/American_highlight.htm

[20] Skytrax- Airline seat pitch data web site.http://www.airlinequality.com/Product/seat_intro.htm

Books

[21] Eveleth,P.B., Tanner, J.M. Worldwide Variation inHuman Growth. 2nd Ed. Cambridge University Press, U.K.

[22]Kroemer,K., Kroemer,H, Kroemer-Elbert,K.Ergonomics. How to design for ease and efficiency. 2nd

Ed. Prentice Hall, New Jersey, 2001.

[23] Woodson, W.E., Tillman, B., & Tillman, P. HumanFactors Design Handbook. 2nd Ed. McGraw Hill, NewYork, 1992

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