An Anlysis of the Visul Demnds Associted with Avition Mintennce Inspectors Gregory W. Good 1, Json J. Nichols 1, Mnoj V. Subbrm 1, Vn B. Nkgwr 2, Ronld W. Montgomery 2 1 The Ohio Stte University College of Optometry, Columbus, OH 2 CAMI, FAA, Oklhom City, OK Bckground: Aircrft mintennce inspectors spend mny hours serching for defects in ircrft. Vision guidelines exist for nondestructive inspection nd testing (NDI/NDT) personnel, but not for visul inspectors. A detiled tsk nlysis is required before job-relevnt vision stndrds cn be developed. This study is descriptive investigtion of the visul tsks of visul nd NDI/NDT inspectors. Methods: Inspectors t ircrft mintennce fcilities were observed performing inspections on ircrft nd ircrft components. Fixtion distnces nd directions were mesured nd recorded for inspectors performing visul, fluorescent penetrnt, nd borescope inspections. Additionlly, visul informtion survey ws completed by 188 inspectors from the different worksites. Results: On over 4000 fixtions during inspection procedures, ner working distnces of 50 cm or less were recorded 66.3% of the time. Intermedite distnces (>50 cm to 1 m) comprised 23.3% of the fixtion distnces nd were most frequently observed in the performnce of borescope nd visul inspections. The men ge of inspectors t these loctions ws 45.1 yers. Conclusions: The primry duty of visul inspectors is the identifiction of defects in ircrft when viewed t ner nd intermedite distnces. Dt from this study support the need for vision stndrds for visul inspectors nd for s the ddition of n intermedite visul cuity requirement to the present distnce nd ner vision stndrd for ll inspectors over 50 yers of ge. INTRODUCTION Mintennce personnel working t ircrft mintennce fcilities my hve primry responsibilities s visul inspectors where they must use only their vision to ssess the condition of ircrft nd ircrft components; or they cn work in res where Non-Destructive Inspections (NDI) nd Non-Destructive Testing (NDT) re performed. In these workres, NDI/NDT inspectors often use highly sophisticted imging nd scnning devices (e.g., borescopes, ultrsonic scns, eddy current imging, X-ry) to id defect detection. However, even for these inspectors, performing simple visul inspection is vitl component used to ensure tht ircrft re sfe to fly. In recent survey of mintennce fcilities, 52% of inspectors were clssified solely s visul inspectors, 36% were clssified s visul nd NDI/NDT inspectors, while only 12% were clssified solely s NDI/NDT inspectors (Nkgwr et l., 2003). Recommended vision stndrds exist for NDI/NDT personnel (Production nd Airworthiness Division, 2001); however, these guidelines do not pper to be bsed upon job-tsk nlysis, which documents viewing distnces required for efficient tsk performnce. Additionlly, no such vision guidelines exist for inspectors who only perform visul inspection tsks. Becuse of the intimcy between the two inspection clssifictions (i.e., visul vs. NDI/NDT), most fcilities use similr testing requirements for both types of inspectors. While their gols re similr, the two jobs re inherently different in terms of the visul tsk nd sophistiction of testing equipment used. To the gretest extent possible, vision stndrds should ensure tht workers hve the necessry visul skills to perform job-relevnt tsks in n efficient nd sfe mnner. For NDI/NDT inspectors, vision skills should be dequte to identify res of concern (i.e., detect potentil defects) nd to determine if further ction is required (i.e., decide if possible defect is within tolernces or if specil tests re necessry) (Drury, 2001). Although the NDI/NDT personnel hve mny tools to id in the detection of defects (e.g., fluorescent penetrnt nd mgnetic prticle inspections, eddy current nd ultrsonic devices, borescopes, mgnifiction ids), simple visul inspection my ccount for up to 80% of ll inspections (Gornson nd Rogers, 1983). With dvncing ge, one grdully loses the norml physiologic bility to focus on ner objects. This condition is termed presbyopi. Beginning t ge 40, individuls often hve difficulty focusing for extended periods t norml reding distnce. For n inspector over 40 yers of ge, the decline in ccommodtion my strt to ffect nerpoint serching. Typiclly by ge 50 lmost ll focusing bility is lost. Bifocl lenses cn provide pproprite focus for given working distnce, for exmple, t 16 inches with +2.5 Diopters (D) reding ddition. For normlly-sighted presbyope, with vision correctble to 20/20, these bifocl spectcles would llow for pssge of the present Air Trnsport Assocition
Specifiction 105 stndrd. Should the inspector be required to view t distnce of 32 inches, however, the serch re would be 1.25 D out of focus in both the distnce nd ner portions of his spectcles. He / she would now be inspecting the ircrft with reduced visul cuity, estimted to be 20/50 to 20/60. The FAA mnges this sitution for pilots 50 yers of ge nd over by requiring tht pilots see 20/40 or better t both 16 nd 32 inches (Nkgwr nd Wood, 1998). This ge-relted requirement is bsed upon the need for pilots to see cockpit instruments t intermedite distnces nd the norml physiologicl chnges tht limit person s bility to focus t ner nd intermedite distnces fter 50 yers of ge. A detiled tsk nlysis with documenttion of required working distnces is not present in the vition literture for NDI/NDT nd visul inspectors. This study investigted the visul tsk performed by vition mintennce inspectors nd looks specificlly t the viewing distnces nd directions required to conduct fluorescent penetrnt, borescope nd visul inspections. METHODS The reserch protocol ws pproved by the Institutionl Review Bord of the Ohio Stte University. Visul nd NDI/NDT inspectors t five ircrft mintennce fcilities were observed s they performed inspection duties on severl types of commercil ircrft (e.g., B727, B737, B767, A320, DC8, DC9, MD80). Vrious mesures of the visul tsks were recorded, long with the specific uxiliry ids used (i.e., flshlight, mgnifier, mesuring rule), during fluorescent penetrnt, borescope, nd visul inspection procedures. Additionlly, visul inspection tsks were divided into two ctegories depending upon the mjor intent of the procedures. These ctegories were termed buy-bck nd primry inspection tsks. Fluorescent Penetrnt Inspections. Fluorescent penetrnt inspections (FPI) were observed t only one mintennce fcility. Inspections were minly performed on engine prts. These prts were inspected t the cse shop or the rotry shop, depending on whether the prt ws rotting or nonrotting engine component. While good prctices for FPI lists 7 modertely independent steps (Drury, 1999), only the inspection (visul detection nd decision) portion of the procedure ws observed nd ssessed. Within both shops, engine prts would move long while suspended from n overhed conveyor. Workers would divert individul prts from the min conveyor nd move it to their worksttions in order to complete the fluorescent penetrnt inspection procedure. Borescope Inspections. Borescope inspections (BI) were observed t 2 of the mintennce centers. The inspection procedure involved using video borescope to inspect internl engine prts (Drury nd Wtson, 2000). Inspectors viewed video monitor s they serched for internl engine defects. At one fcility, the engines were seprted from the ircrft, while t the other, the engines were inspected while still mounted under the wing. Visul Buy-Bck Inspections. Inspections were termed buy-bck when inspectors checked jobs individully completed by vition mintennce technicins (AMTs, i.e., mechnics). These tsks were very specific nd generlly involved repir or replcement of individul prts or ircrft ssemblies. Mny involved the inspectors reviewing the AMT s job crd for repir descriptions t n inspection sttion before trveling to the AMT s work bench or ircrft section. A buy-bck inspection would typiclly lst only 30 to 60 seconds, but could lst severl minutes when complicted visul inspection ws necessry. Visul Primry Inspections. Primry inspections were those tsks where workers checked generl res during the initil phses of mintennce to identify specific types of defects identified on work crds. Overll, these inspections could lst between severl minutes for smll jobs to severl hours for inspections of lrge res. For FPI, BI, nd visul primry inspections, reserchers recorded viewing distnces nd directions t specific points in time while workers performed inspection procedures. Depending upon the type of work nd res under inspection, reserchers would record viewing informtion t 30- second or 1-minute intervls. Therefore, the dt represents viewing informtion similr to tht which would be collected if video recording were smpled t every n th frme. For visul buy-bck inspections, workers would typiclly view the indicted prts for only 30 seconds to severl minutes. Becuse of this, only single fixtion distnce ws recorded for these inspections. For viewing distnce, reserchers indicted the distnce from the inspector s eyes to the visul trget using 7 different distnce ctegories ( 33, 34 to 40, 41 to 50, 51 to 66, 67 to 100, 101 to 200, nd > 200 centimeters). These ctegories represented equl steps in focusing units (i.e., 0.50 Diopters or inverse meters). For this report, the 7 fixtion distnce groups were reduced to 3 by merging dt from pproprite groups. The fixtion distnce dt in this report re presented s follows: ) Ner 50 cm or less, b) Intermedite over 50 cm to 1 meter, nd
c) Fr over 1 meter. For viewing direction dt, up ws mrked when the object of regrd (OR) ws bove the level of the inspector s eyes, down ws mrked when the OR ws between eye level nd the inspector s wist, nd full-down ws mrked when the OR ws below the inspector s wist. A Chi Squre nlysis of the distributions of fixtion distnce nd fixtion direction ws performed cross the three types of inspections (visul, fluorescent penetrnt, nd borescope). Finlly, voluntry survey ws distributed to visul nd NDI/NDT inspectors t the vrious mintennce fcilities tht solicited demogrphic nd refrctive error correction informtion (e.g., glsses, contct lenses, refrctive surgery). RESULTS Dt nlyzed were from 5 mintennce fcilities in the continentl United Sttes. Three of these fcilities were privte, one ws mjor irline, nd one ws t militry instlltion. Survey. The men ge of inspectors responding to the survey dministered t these fcilities ws 45.1 ± 8.5 yers (n = 188), nd survey responses re summrized in Tble 1. Of those responding to the survey (pproximtely 30% of the entire inspection workforce for these fcilities), 49.5% reported wering spectcles for ner work ctivities, 8.0% reported wering contct lenses t some time on the job, nd 6.9% reported to hve undergone refrctive surgery. Approximtely 30% of the respondents wore no refrctive correction t either distnce or ner. For inspectors over 40 yers of ge using nerpoint correction, 35% reported wering single vision lenses, 24% reported wering trditionl bifocls, 35% reported wering progressive bifocls, 4% reported wering trifocls, nd 2% reported wering double bifocls. For those wering contct lenses, 80% reported to wer soft lenses while none of the respondents reported to wer bifocl or monovision contct lenses. A slight mjority of inspectors completing the survey rrely performed ny NDI/NDT procedures. Of the respondents, 57.6% reported tht less thn 10% of their work time is devoted to NDI/NDT procedures. As group verge, however, it ws reported tht 26.8% of overll inspector time ws devoted to NDI/NDT procedures. Observtions. The distribution of fixtion distnces nd directions for visul inspections, fluorescent penetrnt inspections, nd borescope inspections for over 4,000 recorded fixtions re summrized in Tble 2. Fixtion Distnce. For ll inspections, visul detil ws often viewed t norml reding distnces (less thn 50 cm for 66.3% of fixtions). This ws prticulrly true for fluorescent penetrnt inspections where working distnces t 50 cm or less were observed over 93% of the time. On the other extreme, however, ner fixtion distnces were observed for borescope inspections 33.4% of the time. For these inspections, borescope inspectors primrily viewed video monitor positioned t n intermedite distnce. Visul inspection tsks were most often performed t ner viewing distnces (72.2%). Fixtion Direction. With borescope nd fluorescent penetrnt inspections, fixtion direction ws minly confined to norml reding loctions (down position). For both inspection types, workers hd control of the work environment nd could move the visul trget to comfortble position. For visul inspections, workers often hd to position their bodies reltive to fixed visul trget nd, therefore, more vrible fixtion directions were required. This resulted in viewing up nerly 30% of the time with visul inspections nd viewing below the wist nerly 16% of the time. Further nlysis showed tht for the upwrd fixtions, vst mjority (75%) involved focusing within 50 cm. Chi-squre nlysis results cross inspection types re shown in Tble 2. The distributions for both fixtion distnce nd fixtion direction re shown to be different cross the 3 inspection methods. Fluorescent penetrnt inspection is hevily weighted t the ner fixtion distnce in the norml down position. Borescope inspections re more evenly distributed cross ll viewing distnces but re hevily weighted in the down viewing position. For visul inspections, wide distribution is found cross both fixtion distnce nd direction. Tble 1. Survey Responses. Inspectors were those respondents tht reported to perform NDI/NDT or VI procedures over 50% of their work time. Outcome All n = 188 NDI/NDT n = 46 VI n = 103 Men Age (yrs) 45.1 44.3 45.6 t = 0.67, p = 0.50 Glsses for 49.5 % 67.4% 42.7% Ner Inspection Chi-Sq = 7.74, p = 0.005 CL Werer 8.0% 10.9% 5.8% Chi-Sq =1.18, p = 0.277 Refrctive Surg 6.9% 4.3% 8.7% Chi-Sq = 0.90, p = 0.344 T-test nd Chi-squre tests for NDI/NDT nd VI comprison.
Tble 2. Fixtion Distnces nd Directions (percentges). Distnce VI FPI BS All Ner 72.2 93.3 33.4 66.3 Intermedite 18.7 6.5 44.7 23.3 Fr 9.2 0.2 21.9 10.4 Chi-Sq = 620.6, p < 0.001 Position Up 29.0 14.2 8.1 17.1 Down 55.4 85.8 88.9 76.7 Full Down 15.7 0.0 2.9 6.2 Chi-Sq = 494.2, p < 0.001 Chi-squre tests for comprison of 3 type inspections. DISCUSSION The estblishment of vision stndrd shres mny similrities with the determintion of cutoff score for ny bility test. The essentil job functions must be identified s well s the consequences of non-performnce. While the frequency of tsk performnce is n importnt element in setting stndrd, tsk frequency cnnot lwys be equted with tsk importnce. When the consequences of n error re dire (missed crck in criticl component, for exmple), even rrely performed tsk cn drive vision stndrd. The mjority of inspection work performed by ll inspectors in this study ws performed t viewing distnces of less thn 50 cm (i.e., 66.3%). Thus, the essence of this work is the identifiction of defects t ner working distnces. Coupled with the extreme potentil consequences of missing defect, the frequency dt gretly supports the need for nerpoint visul cuity stndrd for visul inspectors who re currently not required to meet cuity requirements t ny distnce. The dt supporting the need for n intermedite visul cuity stndrd is lso strong, especilly for visul nd borescope inspections. Visul inspectors must observe ircrft components tht re difficult to rech nd to visulize. These inspectors often cnnot physiclly position themselves to obtin norml viewing distnces nd directions. Intermedite distnce viewing is often required. For borescope inspections, workers do hve greter control for the inspection. Inspectors cn position television monitors for viewing t convenient loctions, even though the prts inspected cn be reltively inccessible to the inspector. Borescope inspectors, however, often chose intermedite viewing distnces for viewing the monitor to llow for full body movements to more esily hold nd position the borescope probe. The differences in the distributions of working distnces nd directions cross the different types of inspections re due both to the nture of the inspection tsk nd to the control (or lck of control) the inspector hs on the prt being inspected. With FPI, the mjority of the work is done t ner working distnces in norml reding position (down). This ws the cse for fluorescent penetrnt becuse most inspections re done on individul prts tken off ircrft, llowing greter control of prt positioning. Visul inspectors hve the lest viewing flexibility s the object of regrd is often firmly fixed to the ircrft nd inspectors must chnge body nd hed position, often in crmped qurters, to gin n cceptble viewing posture. Nerly 20% of visul inspections re done t n intermedite viewing distnce (between 50 cm nd 1 meter). Visul inspectors often inspect lrge res of n ircrft for crcks nd other defects from intermedite distnces. Becuse longer working distnce trnsltes into smller visul ngles for visul detil subtended to the eye, it could be rgued tht it is more importnt for inspectors to be cpble of cler focusing t intermedite distnces thn it is for ner working distnces. For borescope inspections, nerly onehlf (44.7%) of the viewing distnces were observed to be between 50 cm nd 1 meter. It is cler tht lrge portion of ircrft inspection must be done with fixtion distnce of greter thn 50 cm. Becuse of our norml physiologic ccommodtive bility, if worker under 40 yers of ge cn pss vision stndrd t given distnce using norml, single vision glsses, he/she should be ble to pss the sme stndrd t ll working distnces. For workers older thn 50 yers, however, specilly designed multifocl lenses my be required to llow shrp vision t intermedite nd ner working distnces. As the men ge of surveyed inspectors is 45.1 yers, lrge proportion of inspectors hve lost significnt nturl ccommodtive power. Eyewer must be designed with viewing distnces nd directions in mind. Although the mjority of fixtion directions for ircrft inspection correspond to the norml bifocl position (slightly down), much visul inspection ctivity is directed upwrd (29.0%) nd t intermedite to long viewing distnces (27.9%). Inspectors should thoroughly discuss the vritions in object distnce
nd direction required of their jobs with their eye cre prctitioners. In order to ensure cler nd comfortble vision t ll working distnces, specil eyewer designs my be required. Inspectors older thn 50 yers my require trifocls or progressive ddition bifocls (i.e., noline) to llow cler vision t ll required viewing distnces. As working distnces vry regrdless of the viewing directions, it my be beneficil to use clip-on ner lenses to ccommodte some working distnces nd/or wkwrd directions. A set of clipon lenses of different powers cn be obtined to ensure tht cler focusing is obtinble t ll fixtion distnces. The dt presented supports vision requirements for visul inspectors s well s the ddition of n intermedite visul cuity requirement to the present distnce nd ner vision stndrd for ll inspectors over 50 yers of ge. As inspectors ge, more frequent vision screenings would help ensure tht refrctive correction is dequte to ccommodte the three working distnces. It is impossible to design eyewer, however, tht will llow ll fixtion directions nd hed positions to be cpble of cler vision t distnce, intermedite nd ner distnces. Therefore, worker eduction progrm should be included within the overll vision progrm. Such progrm will help inspectors understnd the limittions of multifocl lenses for vition inspection tsks nd lern wht lens devices re vilble to better ccomplish their visul tsks in sfe nd efficient mnner. Nkgwr VB, Montgomery RW, Good GW, Nichols JJ (2003). A demogrphic profile of nondestructive inspection nd testing (NDI/NDT) personnel: A preliminry report. Federl Avition Administrtion, Office of the Chief Scientist for Humn Fctors (AAR-100), FY03 Avition Mintennce, Generl Avition, nd Verticl Flight. University of Nevd Reno, 10-12 September 2003. Nkgwr VB, Wood KJ. (1998). Clinicl ppliction of new civil irmn vision stndrds nd certifiction procedures. Journl of the Americn Optometric Assocition; 69:144-50. Production nd Airworthiness Division (AIR-200), FAA (2001). Qulifiction Stndrds for Nondestructive Testing (NDT) Inspection/ Evlution Personnel, vi http://www.f.gov/certifiction/ircrft/ndtq UALSTDMEMO.htm. REFERENCES Drury CG. (1999). Humn Fctors Good Prctices in Fluorescent Penetrnt Inspection. Humn Fctors in Avition Mintennce - Phse Nine, Progress Report, FAA/Humn Fctors in Avition Mintennce, vi http://hfskywy.f.gov. Drury CG. (2001). Good Prctices in Visul Inspection. Humn Fctors in Avition Mintennce - Phse Nine, Progress Report, FAA/Humn Fctors in Avition Mintennce, vi http://hfskywy.f.gov. Drury CG, Wtson J. (2000). Humn Fctors Good Prctices in Borescope Inspection. FAA/Office of Avition Medicine, Wshington, D.C., vi http://hfskywy.f.gov. Gornson UF, Rogers JT. (1983). Elements of dmge tolernce verifiction, 12 th Symposium of Interntionl Commercil Aeronuticl Ftigue, Toulouse, Frnce.