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Spatial Disorientation Accidentsin U.S. Army Rotary Wing
AircraftFYs 1996-2000
Preliminary Examination
MethodsSummaries of all class A-C accidents from 1 October 1995 to 31 September 2000 were obtained from the U.S. Army Safety Center.
The minimum standard for this review was that SD was “more probable than not”rather than “absolute certainty.”
MethodsAccidents were classified into one of the following groups:
SD - spatial disorientation was a major or contributory factor of the mishapNon-SD - spatial disorientation did not occurUnknown - the cause of the mishap can not be determined
MethodsThis study used the following definitions of SD:
“The situation occurring when the aviator fails to correctly sense the position, motion, or attitude of his aircraft or himself within the fixed coordinate system provided by the surface of the earth and the gravitational vertical”(Benson, 1978)“The erroneous perception of the aviator’s own position, motion, or attitude to his aircraft, or of his aircraft relative to another aircraft”(Vyrnwy-Jones, 1988)Geographic disorientation (getting lost) was excluded
Data for FYs 96-00Accident data were classified as follows:
Total 505• SD - 133• Non-SD - 355• Unknown* - 17• Total used – 488*Unknown were dropped from this examination
SD Non-SD
Num
ber o
f Acc
iden
ts
0
50
100
150
200
250
300
350
400
450
500
SD played a role in 133 (27%) of the 488 accidents which could be classified.
Results
Tree Object Ground Br/Out Wh/Out Mid Air SD
Per
cent
of S
D A
ccid
ents
0
10
20
30
40
50
60
70
80
90
100Results
Accidents due to inadvertent drift, misjudging distances, white outs, brown outs, and SD.
AH1 UH1 AH64 AH64D CH47 MH47 OH58 OH58D UH60 MH60
Accidents/ 100,000 hr
13.5
4.17
15.83
13.23
22.21
23.80
4.19
25.14
9.90
26.03
SD accidents/ 100,000 hr
4.49
1.04
5.40
5.71
1.79
2.16
8.34
5.95
3.36
11.71
Results
Total and SD accident rates per 100,000 flighthours broken down by individual airframes.
Class A Class B Class C
Per
cent
Per
Cla
ss
0
10
20
30
40
50
60
70
80
90
100
SDNon-SD
Results
The percent of SD related Class As was double that of Non-SD. SD Class Bs were only slightly higher while SD Class Cs were 12% lower than Non-SD.
SD Non-SD
Ave
rage
Cos
t Per
Acc
iden
t (m
illio
ns)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Results
The average cost of an SD accident was more than double that of a Non-SD accident.
Results
SD Non-SD
Ave
rage
Fat
aliti
es P
er A
ccid
ent
0.00
0.05
0.10
0.15
0.20
0.25
SD accidents were 3 times more fatal than Non-SD accidents.
Day Dusk Night
Acc
iden
t Tim
e of
Day
(per
cent
)
0
10
20
30
40
50
60
70
80
90
100
Results
Of the 488 accidents, 315 occurred during the day (65%), 17 at dusk (3%), and 156 at night (32%).
Day Dusk Night
Acc
iden
t Tim
e of
Day
(per
cent
)
0
10
20
30
40
50
60
70
80
90
100SDNon-SD
Percent of SD and Non-SD accidents at each time of day.
Results
AH1 UH1 AH64 AH64D CH47 MH47 OH58 OH58D UH60 MH60
Night Accidents
4
7
39
3
20
8
5
26
36
9
Night SD Accidents
1
4
19
1
3
1
1
10
17
7
*
25%
57.1%
48.7%
33.3%
15%
12.5%
20%
38.5%
47.2%
77.7%
Results
Percent of night SD accidents by airframe
* not normalized by 100,000 flight hours
Aided Unaided Not Reported
Nig
ht T
ime
Acc
iden
ts (p
erce
nt)
0
10
20
30
40
50
60
70
80
90
100
Of the 156 night accidents there were 136 (83%) aided, 15 unaided (13%), and 4 not reported (4%).
Results
Aided Unaided Not Reported
Nig
ht T
ime
Acc
iden
t (pe
rcen
t)
0
10
20
30
40
50
60
70
80
90
100SDNon-SD
Percent of SD and Non-SD accidentsduring each type of night flight.
Results
SD Non-SD
Perc
ent N
VD U
sed
0
10
20
30
40
50
60
70
80
90
100
Results
The percent of SD accidents in which NVDs werein use was double than of Non-SD accidents.
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000
Acc
iden
t Rat
e (p
er 1
00,0
00 h
r)
0
5
10
15
20SD rateOverall rate
Results
Overall and SD rotary-wing accident rates for the past decade.
Discussion
SD accidents are more costly in terms of lives than non-SD accidentsSD accidents are more costly in terms of dollars than non-SD accidents
Preliminary results are similar to reviews byDurnford et al., 1995 and Braithwaite et al., 1977
DiscussionClassic SD accidents were uncommon (1 of 133)Most SD accidents were due to inadvertent drift and misjudging distances (116 of 133)47 % of SD accidents occur at night compared to 27% of non-SD accidents
DiscussionThe % of SD accidents in which NVDs were in use was double that of non-SDComparison with FY 91-95 data showed that the SD accident rate is not decreasingIf anything, since 1995 the SD accident rate has slowly started increasing