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Technical keport Documentation Page 

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\Work was performed under Task AM-A-80/81-PSY-86. ~ 

16. Abstroc;t 

The interest of manufacturing, governmental, and safety personnel using p~int schemes 

on propeller and rotor blades is based on improving the visual conspicuity of those 

blades when they are rotating. While propeller and rotor paint schemes may serve to 

reduce the nwnbe1· of fatalities and injuries due to contact with a rotating blade 

there is little information available regarding analyses of the circumstances 

surrounding such accidents. 

Brief reports provided by the National Transpl'lrtacion Safety Board of all 'propellerto-person• accidents from 1965 through 1979 were examined and analyzed in terms of 

airport lighting conditions, actions of pilots, actions of passengers and ground 

crew, phase of flight operation, weather conditions, and others. Analyses based on a 

total of 319 accidents showed a mar·.<.ed drop in the frequency of '-'propelle&:-to-person_. 

accidents from 1975 through 1978. Several types of educational efforts directed towan 

pilots and ground crew, both prior to and during that 4-year perioci, were examined 

as possible factors contributing to the accident rate decline. Accident pa~.o:erns 

provide a basis for assessing the probable efficacy of various recommendations 

(inc1~ding propeller conspicuity) for further reducing ~repeller-to-person- accident~ 

Ko, Wo•d> 

opeller Accidents 

lot Training 

Safety 

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1

18. Distribut•on Statement 

Document is available to the 

through the National Technic. 

public 

Inforrnatiop. 

Service, Springfield, Virgin a 22161 

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21· No. of Pages 

10 
AN ANALYSIS OF ;:IVIL AV1ATION PROPELLER-'10-PERSON ACCIJENTS: 

1965-1979 

Introduction. 

The interest of manufacturing, governmental, ar.d safety personn~l in 

using paint schemes on aircraft propellers and helicopter rotor blades is 

based on i~proving the visual conspicuity of those blades when they are 

rotating. Greater conspicuity is generally considered essential to reducing 

the number of civil aviation accidents which i~volve fatal or serious injury 

to persons who are struck by rotating propellers and rotor blades. There are, 

however, no Federal Aviation Regulations (FAR's) which specify requirements 

regarding ~he conspicuity of aircraft propellers, although helicopter tail 

rotors are required to be marked ~o that the perceptual disks created by their 

rotation are "conspicuous under normal daylight ground conditions." Interestingly, virtually all U.S. aircraft do have propeller markings, but most of 

these are of factory design; others represent the choice of the owner. Although colors (particular~; YF~low and red) are often used, available data 

(5,6) suggest that black and white markin~s yield the best conspicuity ratings 

from observers. 

While propeller and rotor paint schemes of one kind or another may serve 

to reduce the numbers of fatalities and injuries due to contact with a rotating blade, therE is little information available regarding analyses of the 

circumstances surrounding the accidents which do occur~ Thus, the present 

study ~as designed to explore the frequency, time of day, weather conditions, 

pilot and passenger activities, and other features possibly associated with 

injuries and fatalities due to persons being struck by propeller and rotor 

blades. 

Method. 

Computer retrievals of report briefs of all propeller-to-person 

accidents from 1965 through 1979 were made on special request to the National 

Transportation Safety Board (NTSB). These briefs each contain standard 

information regarding aviatjon accidents (e.g., time of day, statement of 

cause, nature of injuries, etc.). In addition, detailed review of the 

accident files for each propeller or rotor accident during the most recent 

5-year period (1975 through 1979) was conducted to confirm comprehensive 

background information. The complete file was also reviewed for 36 ac...:idents 

from 1965 through 1974 to obtain information which ~~~ not clear in t 

brief3. In 48 other cases, questions werE> raised from review of the ~ .. rief 

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(29 questions abo·.1t magneto switches, 13 about dusk-darkness conditions, and 

1 about whether handcranking was involved), but access to the complete files 

was not possible because th~y had been destroyed at the NTSB Records Center 

(24 of these were between 1965 Dnd 1968). Data were analyzed in terms of time 

of day, actions of pilo~.:s, action of passengers and q.rru.nd crew, phase of 

flight operation, weather conditions, and others. 

Results. 

Tabulations over tht 15-y~ar period 1ielded a total of 319 accidents; 

108 involved fatalities, and 211 resulted in serious injuries (see Table 1). 

All 319 oT these accidents invclved propeller deaths or injuries to single 

persons with the exception of 2 accidents; (i) in 1970 a U.S. helicopter 

delivering food in a foreign country was rushed by a crowd with three injuries 

resulting (two serious, ons minor), and (ii) in 1972 a runaway aircraft (handcranked by a pilot without adequate ~raking zafeguards) ran into two spectators, 

k1lling both. The 319 accidents thus resulted in 109 deaths, while 219 persons 

were seriously injured and 1 sustained a minor injury. Table l also shows a 

marked reduction in accidents during 1975 through 1978. 

TABLE l. NUMBER OF PROPELLER-TD-PERSON ACCIDENTS IN 

GENERAL AVIATION, 1965-1979 

Fatal Serious 

Year Injury Injury Total 

1979 7 15 22 

1978 5 9 14 

1977 5 ll 16 

1976 5 10 15 

1975 4 8 12 

1974 12 18 30 

1973 8 13 21 

1972 12 17 29 

1971 12 15 27 

1970 7 14 21 

1969 5 20 25 

1968 10 12 22 

1967 4 23 27 

1966 8 13 21 

1965 4 13 17 

TOTALS 108 211 319 

Table 2 contains a breakdown of categories of persons injured or killed 

by contact with propellers or rotors. Fifty percer.t of the accidents involved 

passengers and about 20% involved the pilots, followed by ground crew, 

spectators, and a general category (7.5%) termed 11 0ther" (the latter includes 

such persons as drivers of delivery trucks, postal mail loaders, etc.}. 

Table 2 also presents a breakdown of the activities of the individuals 

which were associated with the accidents. More than 25% of the accidents 

2 . 

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TABLE 2. NUMBER OF PROPELLER-TO-PERSON ACCIDENTS INVOLVING FATAL 

AND SERIOUS lNJURIES (1965-1979) BY CATEGORY OF VICTIMS 

AND BY THE ACTIVITIES I~ WHICH THEY WERE ENGAGED. 

(NOTE: Two accidents involved mGre than one victim.) 

Fatal Serious 

Persons Injury Injury Total 

Pilots 16 45 61 

Passengers 57 103 160 

Ground cre111 15 26 41 

Spectators 12 23 35* 

Others 9 15 24 

TOTALS 109 212 321* 

*plus one spectator with minor injury 

Fatal Serious 

Activities Injurl Injury Total 

HanC.cranking 13 56 69 

Jump Starting 1 5 6 

Pilot Check 0 4 4 

Assisting Pilot 27 40 67 

Loading, Delivering 3 8 11 

Walking Spectator 10 14 24 

Enplaning 14 19 33 

Deplaning 35 54 89 

Improper Procedure 0 1 1 

Runaway Aircraft 1 l 2 

Other 4 9 13 

TOTALS 108 211 319 

occurred as a result of deplaning, approxi~rttely 20% involved handcranking the 

aircraft, another 20% occurred when persons were otherwise trying to assist 

the pilot (e.g., by helping to dock a seaplane, removing wheel chocks, etc.), 

about 10% occurred during enplaning, and the remainder were divided among 

walking visitors, delivery men anC loaders, persons trying to jump start the 

aircraft engine, pilots checking their aircraft while the engines ~ere running, persons hit by a runway aircraft, and a general category (4%) of 11 othern 

(including the three injuries noted above resulting from the crowd rushing a 

food-bearing helicopter, c. p1lc-t trying to close the canopy while the aircraft was moving, etc.). OVer half of the handcranking accidents involved 

pilots, and 22% comprised ground crew, vhile the remainder were equally 

divided between passengers and "others." 

Other than the 2 instances of a runaway aircraft (resulting from the 

pilot's handcranking without adequate braking), only 17 other accidents 

involved an aircraft in a movement pa~tern (eag •• taking off, in flight, 

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landing). Thus, the vast majority of the 319 propeller-to-p:=~rson accidents 

occurred while the aircraft was stationary. Heliccpters were involved in 46 

(14%) of the accidents and seaplanes in 21 (7%). About two-thirds of the 

helicopter accidents involved the tail rotor and half of all rotor accidents 

were fatal. Moreover, about one-third {N=l5) of those helicopter accidents 

occurred during deplaning and about 20% durint enplaning (N=:9), all of these 

duriPg daylight hours. Of the accidents involving seaplanes, (i) 86% of the 

total occurred during deplaning and "assisting the pilot 11 activities, (ii) 

all of the deplaning (N=lO) and enplaning (N=2} accidents were in daylight 

hours, and (iii) almost half (N=lO) of the seaplane accidents occurred in the 

states of Alaska and Washington. 

Several factors which might have contributed to these propeller-to-person 

accidents were examined. Alcchol involvement was reported only 11 times, but 

8 of the 11 were fatal; of these 11 accidents, almost half (N=S) occurred 

during the daytime (between 0730 and 1730). Alcohol involver.uent may be underestimated since it is relatively unlikely that a pilot would be subjected to 

a blood or breath test if the passenger was f2tally injured. Rain, snow, or 

fog was present in only 9 accidents and ground that was wet, icy, or snow 

covered was reported 13 times. Thus, although these factors were infrequently 

involved, they may well have made the difference in whether or not those 

particular accidents occurred. Of perhcps greater significance is the fact 

that at l~ast on~-fourth of the accidents occurred du~ing the hours of dusk 

or darkness (the proportion is probably higher, but the NTSB brief reports 

do not provide sufficient data to verif:r 11probables"). With respect to the 

87 accidents in the dark, more (29) occurred with persons attempting to assist 

the pilot than for persons depl::ming (27), enplaning (13), or for "other" 

reasons. Overall, these findings indicate that about 40% of accidents involving persons assisting the pilots, 39% of enplaning accidents, and 30% of deplaning accidents occurred at night when ordinary propeller conspicuity (even 

at a well-lighted airport) would be considerably reduced. 

Discussion. 

The data show clearly that individuals most at risk for a propeller-toperson accident are passengers who are either deplaning or attempting to 

assist t~e pilot. That the accident frequency is high for these groups is 

perhaps surprising since, in some respects at least, pilots would have 

reasonable, direct, and timely opportunities to control, caution, or counsel 

passengers regarding safe procedures in deplaining or in providing assistance 

with the aircraft. Two features of this finding seem clear: (i) pilots have 

a major responsibility for actively seeking to prevent propeller-to-person 

accidents to their pasaengers, and (ii) the means by which such accidents 

could be reduced or virtually eliminated require no esoteric equipment and 

are relatively simple (careful instruction of passengers prior to their deplaning; either not using passengers as assistants or instructing them more 

carefully regarding hazards; and having engines shut down prior to loading 

or unloading passengers). 

Another feature of significance in 

which occurred at dusk or in darkness. 

4 

the data is the number of accidents 

While there is a significant reduction 
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in general aviatior. activity during these hours, over 27% of the propellerto-person accidents occurred during periods of reduced natural lighting 

(specified ln the accident report). This percentage is probably an underestimation since time-of-day da:a ~n the NTSB brief reports (taking into 

.a~~QIJ.D.t. t.~.e WRn.t.'t\ tJ.f t..l;J.~ :r~-a'!: .a.t'.<i t.~e lt;:~.eat."\.Qn. a.f t.b.~ ac:.~i.d~ut) S.IJ_'hCf.,e.s.t the. 

possibility of additional dusk oL nighttime accidents which were unverifiable because the complete file for a number of these accidents had already 

been destroyed. The ratio of accidents which occurred to pe=sons assisting 

the pilot virtually doubled &t night as compared with daytime (33.3% vs. 

J 6 .. 85;); moreover, passengers were involtred in proportionately more accidents 

at night than in the daytime--the pilots proportionately less--and the rati~ 

of enplaning accidents was also considerably higher in redt:.ced illumination 

(15% vs. 9% in daylight). The increased nighttime accident rate for enplaning passengers suggests that propeller markings, ~hich would be visible durin> 

the daytime but not- in reduced illumination may have been effective signaling 

d~vic~s to pass~ngers a??Yoaching the ~i~craft in daylight. It is also ~orth 

noting that the absolute number of nighttime deplaning accidents has remained 

relatively constant over the years (9 during 1965-69; 10 during 1970-74; c. 

during 1975-79) despite reductions in dayti~e deplaning totals and in the 

overall number of propeller-to-person accidents. 

Major Accidents Categories: Perhaps surprisingly~ more than twice a£ 

many accidents occurred during the handc1·anking of an aircraft than occurred 

during passenger enplaning. Pilots were most often victims of handcranking 

accidents (56% of such cases) followed in frequency by ground crew members 

(22%). Of the 69 accidents of this type, the magneto switches were confirmed 

as "on11 in 30 c.ases, but "offn {and t.he:-ref<Yre probably d.~f~ctive) in. 10 case.s, 

and could not be assessed in the other 29 cases due to the unavailability of 

the full accident report. Moreover, more than 80% of the handcranking 

accidents occurred with "nose wheel" (tricycle gear) aircraft as compared 

with "tail wheel',_ (cor.ventional gear) configurations. And the proportion of 

h~ndcranking accidents involving theee closer-co-the-ground propellecs has 

increased from 68% (1965-69) to 75% (1970-74) to 94% (1975-79). 

Among all propeller-to-per8on accidents involving pilots, most occurred 

during handcranking (64%), followed in frequency by deplaning (18%) activity. 

As noted above, passengers were involved most often in de~laning accidents 

(49%), followed by accidents which occ~rred while they were attem?ting to 

assist the pilot (22%), and while enplaning (20%). Almost all propeller-toperson accidents involving ground crew occurred while they were assisting the 

pilot (61%) or attempting to handcrank the propeller (37%). The majority of 

acciden~s to spectators {b3io) occurred while tbey were walking arounU aircraft. 

Changes in the Accident Rate: The annual tabulations show a marked drop 

in the number of propeller-to-person accidents during 1975-1978 when they 

ave<aged 14 per year. During the two prior 4-year pPricds (1971 through 197~ 

1967 through 1970) they averagP~. en all annual basis, approximately 27 and 24 

accident~~ ~cov~c~ively. Rowever, in 1979, ~he numb~r rose ~c 22 a~c~dents, 

closely approximating those earlier, higher levels. 

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The factors responsible for the 1975-1978 decrease in accidents are not 

readily isolated. Careful ex.arniiiati::m of the categorized data revealed that 

the decrease was not due to a drop in any specific conditions or activities 

surrounding the accidents: but t0 an overall drop in the number of accidents 

across the various defined categories, (The only notable changes were a drop 

in the percentage of accidents involving rotor blades and an increase in the 

percf:!ntage of accidents involving seaplanes.) A search of the aviation 

literature yielded no information that might have influenced general aviation 

pilots regarding the sa~ety hazards of propellers. However, a numb2r of 

contacts with FAA personnel involved with standards and accident prevention 

during that period led to th~ piecing toqethe~ of.several activit~es and 

events that appear to comprise the best assessment of factors which influenced 

the 4-year decline in the number of propeller-to-person acciaents. 

In March 1968, the ~ AA began a 2-year test program to pr._ nr-+:e safety by 

educating general aviation pilots on accident prevention throug~. clinics, 

seminars, and lectures. This Accident Prevention Program (APr) was tested 

in the Central and Southwest FAA regions until March 1970, when it was judged 

as successful in reducing aircraft accidents by improving the attitudes and 

behavior of pilots through increased knowledge and proficiency. Based on 

this favorable assessment, the APP concept was officially expanded to nationwide status during 1911, hut ~as not in full O?~Yation unti~ the ~~tter part 

of 1972 or, perhaps, early 1973. 

The FAA was obviously actively aware of the problem of propeller 

accidents, initiating a defined effort by the APP in the early 1970 1 s to 

reduce the number of such accidents. The APP specialists were provided with 

various types of educational material relating to the hazards of propellers. 

The most dramatic educational tool was a fort:nitously recorded film of an 

actual handpropping accident ~at vccurred in California in 1967. The pilot 

involved handpropped his engine with an inexperienced passenger at the 

controls, without having the wheels chocked or the plane tied down. The 

film shows the pilot har,ging on to the plane as it spins in a circle on one 

wheel until the centrifugal force throws him on the ground where he is struck 

by the plane. As the pilot lies on the ground, seriously injured and covered 

with blood, the runaway plane is finally stopped after running into several 

parked aircraft. The film is a very powerful demonstration of one hazard of 

handpropping, although the accident depicted is obviously not the most 

familiar sequence of events for propeller-to-person injuries. This film was 

available in 1969 but did no~ get wide national exposure until after the APP 

program went nationwide in lq71. lt was then shown frequently by the APP 

specialists in the safety clinics (one estimate is that the film was being 

shown at l~ast twc times a week by 85 APP specialists ac~oss the co~~try). 

The handprop fi~ was mentioned by almost every FAA person we contacted, and 

was especic!ly emphasized by former APP specialists who had been in the field 

during ~r.at time, as a definite factor contributi~g Lo the decline in the 

prope'lev accidents. This contribution seems likely if one allows for a 

time lag of about 18 months before a new program begins to show an effect. 

6 

~-...--------------__:-~·.:.·:.-_-~·:::·:;:·~~;,~~~':!!1-@.'<-t:·~!l·~~~~;~:::;.~~.:;·~~ ... :::.~,i7:=:.·:: ·. ,-., ., < 
In addjtion to the film, several posters and handouts relating to the 

dangers of propellers were distributed during the safety clinics from 1971-

1974. One of the handouts released in 197~ was a special bulletin (Beware 

of Propeller Accidents) that listed several hazardous practices for pilots 

tJ avoid in order to prevent propeller accidents. Accident prevention 

specialists also discussed actual propeller accidents durittg the clinics~ 

ern?hasizing the measures that ~ould have ~een taken to prevent the accidents. 

Besides emphasizing the importance of reducing propel'!.er accidents 

through the APP, the FAA issued an advisory circular (2) on propeller-toperson accidents "Hazards of Rotating Propeller" in June of 1975: revised 

versions of the circular were published in 1976 (3) and 1979 (4). The 

original 2ircular discussed the frequency of propeller accidents, emphasizing 

the fact that all such accidents could be prevented with proper education 

a:1d disci pi ine. The circular warned of the power of the rotating p!""opeller 

and the ~ikelihood that a propeller accident would result in serious or fatal 

injury. Special warnings and pr~ventive rueasures were listed for nonflight 

c:.rer.r personn~ 1, airc:.re.ft sexvic:e "?erscnn.el, fl i.ght -persoa.nel and flight 

instructors \V'hich, if followed, would probably be effective in reducing 

propeller-to-person ~ccidents. The procedure referred to training of nonflight crew, the provision of safety barriers and markings on ramps and 

landing areas, the development of specific safety habjts by aircraft service 

pernonne1, education of student pilots by flight instructors, and checklist 

tests a~d close supervision of passengers and others by pilots. 

The 1976 version of the circular (3) was titled "Hazards of Rotating 

Propeller and Helicopter Rotor Blades" and, as the title implies, added 

specific suggestions regarding rotor blades (e.g., "tail rotor danger areas 

should be c1-ca:r1y ma-rked on ram.'? areas. 11 ), pro-pe.r \lse of l·~"he.el c.h.oc.ks, 

maintenance of propeller markings to insv.re conspicui ty, and tests for 

faulty ignition switches. The 1979 version (4) presented, for the first 

time, a nine-item breakdown of ev2nts leading to propeller-to-person 

accidents. 

Copies of the 1975 circular were distributed at safety clinics and 

meetings across the country. Although the number of propeller accidents had 

already shown evidence of decline during the fir3t half of 1975, the release 

of the 1975 circular and its subsequent revisions in conjunction with the 

aforementioned films, handouts, and lectures probably worked together to 

effect a ~educed p'opelle,-to-pe~son accident rate through lq78. 

~fuile it seems unlikely that the maintenance over a 4-year perio~ (1975-

1978) of a substantial decrease in the absolute number of propeller-to-person 

accidents would be due to chance fact~rs, the 1979 data sbow a sharp increase 

in such accidents. It is possible that this 1-year increase is an artifactual 

variation; if it is not, it suggests that the various factors that were 

operating to keep the number of accidents at a lower level have either declined in their effectiveness or are no longer being used. If our assessment 

is correct that concerted educational attention to the dangers of ~ropellPr 

accidents has been effective in reducing propeller-to-person accidents, 

then tbese educational methods should a~ain be vi~a~ousl~ ?U~sued~ 

7 
Methods of Further Reducing Propeller-To-Person Accidents: The findings 

af this study suggest that propeller conspicuity probably reduces accidents 

(based on the higher nighttime rate of enplaning accidents). There are data 

available (4,o) which indicate the type of markings that most readily catch 

the eJe and those data shou~1 be used by manufacturers to ma~k pro?~l~ers~ 

An FAR specifying such requirements would probably be needed to stimulate the 

use of the most approrriate conspicuity scheme~ 

The Flight Instructor's Handbook (1) cculd explicitly prP~ent the need 

for appropriate instruction regarding procedures for handcrank.i.ng and cautions 

in "pulling the propeller through two revolutions" in cold weather (this handbook makes no mention of either activity). The problems associated with these 

two similar activities could be tersely and effectively stated for educatio11al 

purposes. Similarly, this handbook could also provide a brief discussion of 

the responsibility of the pilot for the safety of his passengers and the need 

to safeguard their entry and departu~e from the aircraft. The dangers associated with having untutored passengers assisting in starting or tying down 

an aircraft could be succinctly and effectively noted. We recommend such 

additions to the handbook. Also, questions on written tests for all pilot 

applicants shou.ld require responses based on an t.:nderstanding of the responsibilities of the pilot for the safety of passengers, enplaning, deplaning, 

or assisting with the aircraft. 

In addition to the methods noted above, attention needs to be directed 

to'-Tard the education of ground ere~ 1d aircraft employees and to "refresher" 

education of pilots. Warning signs might be effective if placed (i) in waiting areas ~here passengers could read the~ aJd (ii) on the inside of aircraft 

doors. 

Requiring t:ha.t pilots turn on the rotclting beacon to indicate engine 

operation (a practice already followed by some pilots and encouraged by som~ 

airpcrt operators) might also be helpful. 

On the more technical side~ the development of auditory or visual warning signals might be explored to indicat~ that aircr~ft doors are open while 

engines are running. Another technical approach that might be effective would 

be the development of additional lighting of the propeller blades (e.g., by a 

wing light aimed at the blades, switch-operated by the pilot) to increase 

conspicuity at dusk, in darkness, or in otherwise reduced illumination condition. Other possible developments include: (i) r~opeller markings on the 

side of the ~lades facing the pilot with patterns such that the markings 

would be visible to the pil~t only ac low (idling) propeller speed, but not 

at taxi, takeoff, or cruising speeds; (ii) markings on propeller 3~inners 

wh1ch are forward of the pilot, similar to those on the propeller blader, to 

increase conspicuity; and (iii) back-lighting (switch-operated by the pilot) 

of the propeller spinner, modified by ":ranslucent patterns, to create a 

conspicuous configuration particularly in reduced lighting. 

8 

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Smmna ry. 

ln response to the nLunb~r of fatal and serious propeller-to-person 

acciOents, the ~AA took several actions in th~ early 1q7o~s, designed to 

reduce propeller accident rates. The actions were primari]y educational 

and were 1arg~1y effected through the Accident Prevention Program. The 

methoCs included lectures, handouts, posters, a film depicting an accident 

resulting from improper handpropping~ and the release of FAA advisory 

circulars on the hazard of propellers. It seems probable !:hat the comtiT ion 

of ~ho~e actions resulted in the significant cirop in the number of propeller 

accidents in the 4-year period from 1975 through 1978. Surp1ementary means 

of further reduciug pr-opeller-to-person accidents include additions to the 

flight instruct0r's manual and the F1ight Training Handbook, strategically 

placed warr..ing sigr~s, and specified techn~ cal developments. The factors 

associated with propeller-to-person acciients clearly assign considerable 

responsibility to pilots to insure safety of their passengers in this regard. 

9 

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REFERENCES 

l. Depar"t.ment of Transportation, Federal Aviati01~ Administration, 1969. 

Flight Instructor's Handbook, AC 6l-l6A, Flight Standards Service, 

Washington, D.C. 

2. Department of Transportation, Federal Aviation Administration, 1975. 

3. 

4. 

5. 

Hazards of rotating propellers. Advisory Circular, No. 91-42, (AFS-C30) , 

June 17, 1975, Washington, D.C. 

Departtnent 

HnzarQs of 

(AFS-830) , 

Department 

Hazards of 

(AFS-830), 

welsh, K. 

assesment 

Office of 

of T~ansportation, Federal Aviation Administration, 1976. 

ro-cating propeller and helicopter rotor blades, AC No. 9l-42A 

October 19, 1976, Washington, D.C. 

of Transportation, Federal Aviation Administration, 1979. 

rotating propeller and helicopter rotor blades, AC No. 91-42B, 

Apri~ 25, 1979, Washington, D.C. 

W., J. A. Vaughan, and P. G. Rasmussen~ 1978~ Conspicuity 

of selected propeller and tail rotor paint schemes. F~~ 

Aviation Medicine Report No. M'l-78-29. 

6. Whiteside, T. C. D. 1973. Markings for propeller conspicuity. 

AGRAD Advisory Report No. 56. 

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