DOT/FAA/AM-09/2 Office of Aerospace Medicine Washington, DC 20591 The Outcome of ATC Message Length and Complexity on En Route Pilot Readback Performance O. Veronika Prinzo Civil Aerospace Medical Institute Federal Aviation Administration Oklahoma City, OK 73125 A.M. Hendrix R. Hendrix Hendrix & Hendrix Roswell, NM 88201 January 2009 Final Report OK-09-0434 NOTICE This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The United States Government assumes no liability for the contents thereof. ___________ This publication and all Office of Aerospace Medicine technical reports are available in full-text from the Civil Aerospace Medical Institute’s publications Web site: www.faa.gov/library/reports/medical/oamtechreports/index.cfm Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. DOT/FAA/AM-09/2 4. Title and Subtitle 5. Report Date The outcome of ATC message length and complexity on en route pilot January 2009 6. Performing Organization Code readback performance 7. Author(s) 8. Performing Organization Report No. 1 2 2 Prinzo OV, Hendrix AM, Hendrix R 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) 1FAA Civil Aerospace Medical Institute 2Hendrix & Hendrix P.O. Box 25082 Oklahoma City, OK 15 Circle Drive 11. Contract or Grant No. 73125 Roswell, NM 88201 12. Sponsoring Agency name and Address 13. Type of Report and Period Covered Office of Aerospace Medicine Federal Aviation Administration 800 Independence Ave., S.W. Washington, DC 20591 14. Sponsoring Agency Code 15. Supplemental Notes This work was performed under Task AM-B-06-HRR-516. 16. Abstract Field data and laboratory studies conducted in the 1990s reported the rate of pilot readback errors and communication problems increased as controller transmissions became more complex. This resulted in the recommendation that controllers send shorter messages to reduce the memory load imposed on pilots by complex messages. More than 10 yrs have passed since a comprehensive analysis quantified the types and frequency of readback errors and communication problems that occurred in the en route operational environment. Hence, a content analysis was performed on 51 hrs of pilot and controller messages that were transmitted from five en route facilities in the contiguous United States between March and August 2006. This report contains detailed and comprehensive descriptions of routine air traffic control (ATC) transmissions and how ATC message complexity and message length affected pilot readback performance. The results show that message complexity had a statistically significant effect on the production of errors of omission only, while message length affected both the production of errors of omission and readback errors (substitution and transposition errors). When pilots requested that controllers repeat their messages, often these messages included the names of fixes, waypoints, and intersections, as well as the name of the next controlling sector or facility. Five recommendations are made: (1) No more than three aviation topics should be included in an ATC transmission. (2) A route clearance should be given as a stand-alone transmission. (3) The names of all fix, waypoint, location, and other identifiers should be repeated, and if necessary, spelled out following their first recitation. For example, “CLEARED DIRECT COBAD THAT’S CHARLIE OSCAR BRAVO ALFA DELTA” or “CLEARED DIRECT COBAD C-O-B- A-D.” (4) Slang should not be used or accepted as part of aviation phraseology. (5) Effort should be undertaken to reduce excessive words/phrases — on, your, to, is, etc. 17. Key Words 18. Distribution Statement Communications, ATC Communication, Document is available to the public through the Defense Technical Information Center, Ft. Belvior, VA Air Traffic Control 22060; and the National Technical Information Service, Springfield, VA 22161 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 38 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized CONTENTS The Outcome of ATC Message Length and Complexity on En Route Pilot Readback Performance. 1. METHOD . 3 . Materals. 3 . Subject.Matter.Experts.(SMEs). 4 . Procedure. 4 . Sector.Descrptons. 6 RESULTS . 7 . Routne.ATC.Communcaton. 7 . Analyss.of.Plot.Faulty.Readback.Performance. 10 . Message.Length.and.Plot.Readback.Performance. 14 REFERENCES. 19 Appendx.A . Gude.to.the.Computaton.of.Complexty:.ATC.Instructon/Clearance.Avaton.Topcs. .A1 Appendx.B . Gude.to.the.Computaton.of.Complexty:.ATC.Advsory.Avaton.Topcs. B1 Appendx.C . Gude.to.the.Classficaton.of.Plot.Readback.Errors:.Instructon/Clearance.Avaton.Topcs . .C1 Appendx.D . Readback.Error.Classficaton.Gude:.Advsory.Avaton.Topcs. D1 EXECUTIVE SUMMARY Ths.report.descrbes.and.summarzes.51.hrs.of.ar.traf- Readback.errors increased.once.ATC.messages included. fic.control.(ATC).communcaton.that.occurred.durng. two.or.more.ATs ..The.most.common.readback.errors. normal,.day-to-day.operatons.at.five.dfferent.en.route. nvolved.alttude.and.alttude.restrctons,.followed.by. centers.between.March.and.August.2006 ..On.average,. changes in.rado.frequency,.route/poston.clearances,.and. an.arcraft.requested.and.receved.ar.traffic.servces.every. altmeter.settngs ..Some.of.the.readback.errors involved. 2.mn.4.s,.wth.approxmately.10.messages.exchanged. slang ..That is,.an.ATC instructon.to.“contact.center.on. from intal.contact.to.the.transfer.of.communcatons .. one.one.nner.pont.zero,”.was.occasonally.read.back.as. The.most.frequently.transmtted instructons involved. “nneteen.zp”.or.“nneteen.nothng .”.What is.worrsome. changes in.alttudes.and.swtchng.plots.to.another.rado. for.avaton.safety is.that.other.plots.may.not.understand. frequency .. these.types.of.readbacks.(especally.plots.who.are.less. Unlke.the.findngs.reported.by.Cardos.(1993).where. proficent in.avaton.Englsh.or.makng.ther.first.flghts. 78%.of.the.ATC.messages involved.one.or.two.peces.of. nto.the.U .S .) . nformaton.(e .g .,.“contact.center.on.one.one.two.pont. A.common.practce.among.plots is.to.acknowledge. three.four”.=.1.pece.of informaton,.whle.“contact.[name]. controller instructons/advsores.wth.ether.ther.call. center.on.one.one.two.pont.three.four”.=.2.peces.of. sgn.only.or.ther.call.sgn.plus.roger/wlco ..Also.com- nformaton),.we.found.that.less.than.1%.of.the.control- mon is.a.response.such.as.“DOWN TO TWO FIVE ZERO”. lers’.messages.had.only.one.or.two.peces.of informaton. (when. acknowledgng. an. nstructon. to. reduce. speed. (of.the.two.examples,.the.first.had.a.complexty.value.of. or.assgnment.of.a.new.alttude).and.partal.readback. 6,.and.the.second.had.a.complexty.value.of.7) ..In.ths. (respondng.to.only.one.of.two.or.more instructons) .. report,.84%.of.the.controllers’.transmssons.contaned. These.examples illustrate.plot.readbacks.that.mght.leave. only. one. avaton. topc. (AT). (e .g .,. alttude,. headng,. the.controller in.doubt.of.plot.understandng.and.may. speed),.whle.messages.wth.two.ATs.occurred in.14%. thus.adversely.affect.safety . of.the.other.transmssons . Possbly.to.avod.the.rsk.of.ether.readng.back.the. We.also.report.a.10 .2% increase in.full.readbacks.and.a. contents.of.an.ATC.transmsson.meant.for.another.ar- 3 .4%.decrease in.partal.readbacks ..Moreover,.plots.who. craft.(stolen.transmsson).or.readng.back its.contents. provded.a.full.readback.also included.the.complete.call. ncorrectly,.plots.asked.the.controller.for.ether.a.full. sgn in.approxmately.64%.of.ther.responses ..The.fact. or.partal.repeat.of.the.orgnal.message ..Of.these.112. that.call.sgns.were.excluded in.10%.of.ther.readbacks. plot.requests,.five involved.a.call.sgn.msspoken.by.the. and. .2%.of.the.spoken.call.sgns.were.unntellgble.leaves. controller. to. whch. the. plot. wanted. confirmaton. of. room.for improvement ..Unfortunately,.both.reports.show. the.message’s.recpent ..A.closer.look.at.requests.showed. the.number.of.unacknowledged.ATC.transmssons.at. that.67 .5%.had.ether.a.fix/ntersecton.or.faclty.name. slghtly.more.than.3% . ncluded.as.part.of.ther.content.—.and.many.of.these. Approxmately.71%.of.the.plot.responses.contaned. messages involved.route.clearances.and.the.transfer.of. faulty.readbacks.—.67 .4%.contaned.one.or.more.er- communcatons .. The. names. of. locaton. dentfiers,. rors.of.omsson.that.could.be.attrbuted.to.ncreases.n. fixes,. ntersectons,. navgatonal. ades,. etc .. are. crtcal. the.complexty.of.ATC.messages ..Changes in.message. to.navgaton;.thus,.plots.were.prudent in.requestng. complexty.alone.had.no.statstcally.sgnficant.effect.on. ether.the.repetton.or.confirmaton.of.prevously.heard. the.producton.of.readback.errors.(e .g .,.the.substtuton. dentfiers . or.transposton.of.numbers in.the.controller’s.orgnal. Based.on.our.findngs,.we.recommend.that: transmssons) .. 1).No.more.than.three.ATs.should.be included in.an. Readback.errors.comprsed.the.remanng.4 .0%.of.the. ATC.transmsson ..2).Route.clearances.should.be.gven. plots’.faulty.readbacks.—.78%.resulted.from.a.combna- separately.as.stand-alone.transmssons ..3).The.names. ton.of.an.error.of.omsson.plus.one.or.more.substtutons. of.all.fixes,.wayponts,.locatons,.and.other identfiers. (89%).or.transpostons.(11%) ..Unlke.message.complexty,. should.be.repeated,.and if.necessary,.spelled.out.fol- message.length.affected.both.the.producton.of.errors.of. lowng.ther.first.rectaton ..For.example,.“CLEARED omsson.and.readback.errors ..There.were.more.errors.of. DIRECT COBAD – CHARLIE-OSCAR-BRAVO-ALFA-DELTA,”. omsson.as.ATC.message.length increased.from.short.(1.AT),. or. “CLEARED DIRECT COBAD – C-O-B-A-D COBAD .”. 4). to.moderate.(2ATs),.and.long.(3.or.more.ATs) ..Redundant. Slang. should. not. be. accepted. by. ATC. as. part. of. a. nformaton.mght.be.elmnated.to increase.the.economy. plot.readback . of.capacty.lmtatons.of.verbal.workng.memory .. v THE OUTCOME OF ATC MESSAGE LENGTH AND COMPLEXITY ON EN ROUTE PIlot READBACK PERFORMANCE Many attempts to communicate are nullified by saying too much.