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