The Economist - UK (2019-06-01)

The EconomistJune 1st 2019 Technology Quarterly |Aviation 3

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nmarch 10tha Boeing 737 max, thelatestversionofthat

firm’sbestsellingnarrow-bodiedairliner,fellfromtheskyin

Ethiopia.All 157 soulsonboardwerelost.Thisfollowedthecrash

offthecoastofJava,lessthanfivemonthsearlier,ofanother 737

max. Thedeathtollthenwas189.Theimmediatecauseinboth

casesseemstohavebeena faultysensorfeedingfalsedatatoan

avionicflight-managementsystemthathad,inturn,hadnewsoft-

warewhichpilotshadnotbeenbriefedabout.Theflight-manage-

mentsysteminsistedonoverridingtheactionsofthepilots,who

didnotknowhowtorespond.Thisprecipitateda stallratherthan,

asintended,preventingone.

Thesetwotragediesilluminatethetensionbetweenconserva-

tismandinnovationthatliesattheheartofcivil-aviationtechnol-

ogy.Asa characterin“TheLeopard”,a novelabouttherevolution-

aryeventsofItaly’sunificationinthe19thcentury,declares:“Ifwe

wantthingstoremainastheyare,everythingneedstochange.”At-

temptsbytheindustrytofollowthatadviceseemtohavebeen

whatultimatelycausedthesecrashes.

The 737 goesbackmanyyears.Itwasconceivedinthe1960s,

whenenginesweresmallerandpassengersgenerallyembarked

anddisembarkedusingstaircaseswheeledinforthepurposerath-

erthanairbridgesconnecteddirectlytoa terminalbuilding.Small

enginesallowed,andstaircasesencouraged,a designthatkeptthe

fuselageclosetotheground.

Bythetimethe 737 maxwasbeingplanned,thishadchanged.

Modernturbofanengineswithwideairintakesrequired,andair-

bridgespermitted,alterationstotheairframethatalsoalteredits

handlingcharacteristics(itstrim, touse thejargon).To keep

thingsastheywere,andavoidpilotshavingtorecertifytoflythe

newversion,itsavionicsoftwarewastweakedtomakethenew

plane’strimfeel,toa pilot,liketheoldplane’s.Thatwouldhave

beenfineaslongasthesensorsfeedinginformationtothoseavi-

onicsworkedproperlyandthepilotsthemselvesknewwhatwas

goingon.Buttheydidnot.

Thecaseofthe 737 maxisanextremeexampleofconservatism

atworkinaircraftdesign.Butretainingthefamiliarisa recurring

theme.ABoeing707,theplanethatusheredinmassinterconti-

nentalairtransportinthe1950s,appearstotheuntutoredeye

muchlikethecurrentofferingsofBoeingandAirbus,theworld’s

principalmakersofairliners.Botholdandnewareportholed

tubesthathavetwoswept-backwingsstickingoutoftheirsides

abouthalfwayalong.Theyhavethreestabiliserfins—twohorizon-

talandonevertical—atthestern.Podscontainingtheirengines

hangonpylonsfromtheirwings.

Festinalente

Attemptstochangethisarrangementhavebeenproposed—most

notablyBoeing’sdelta-wingedSonicCruiserintheearly2000s.

ButapartfromConcorde,a supersonicaircraftinwhichthedelta-

wingedarrangementwasimposedbythelawsofphysics,such

changeshavenevergotanywhere.Engineersknowhowtokeepit

safe,andtheworld’sairportshavegrowninsynergywithit.Be-

neaththisconservativegeometry,however,airlinertechnology

hasimprovedenormouslyandisstillimproving.Bettermaterials

Thefutureofflight

Despite appearances, aircraft have changed a lot—and will soon change more, writes Geoffrey Carr

Aviation

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