Page 113 - JSOM Winter 2019

FIGURE 2 T10 (left) and T-11 (right) parachutes. FIGURE 3 The mechanism of high-altitude entanglements. Jumpers
exiting from opposite doors could collide in the entanglement area if
exiting at the same time. Figure modified from Hadley and Hibst. 17

Entanglement Area

Exit Door

Exit Door

daytime, administrative/nontactical jumps were considered
in this study to ensure jump conditions were similar for the
two parachutes. It was found that injury rates were 44%
lower with the T-11 compared with the T-10 (2.9 vs 1.6 inju-
ries/1000 jumps, risk ratio [RR] [T11/T10] = 0.56, 95% confi- FIGURE 4 Paratrooper preparing to exit aircraft with static line in
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dence interval [CI] = 0.32–0.99). The operational unit study improper position. Figure from Heckman and Levine.
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involved the 82nd Airborne Division and 18th Air Support
Operations Group and was conducted over a 3.5-year period
while the Army was transitioning from the T-10 to the T-11
parachute. During this time jumps were conducted with both
parachute systems. Investigators found that overall injury in-
cidence was 43% lower with the T-11 parachute (9.1 vs 5.2
injuries/1000 jumps, odds ratio [T11/T10] = 0.58, 95% CI =
0.48–0.69). The lower injury rate was found under virtually
all operational conditions including day and night jumps, with
and without combat loads, with different aircraft, and under
varied conditions of wind and temperature. In summary, direct
comparisons of the T-10 and T-11 parachutes during airborne
training and in operational units demonstrated that the T11
had a substantially lower overall injury incidence than the
T10. The T-11 parachute has now totally replaced the T-10 as
the US Army’s parachute for mass tactical operations.

Aircraft Exit Procedures
occurred, the arm could be forcefully abducted by the static
A rare event during military airborne operations is an entan- line as the jumper exited the aircraft leading to a traumatic
glement. An entanglement occurs when the parachutes of two injury of the upper arm or shoulder. 18,19 In 1994 the US Army
or more jumpers become intertwined changing parachute adopted a procedure in which the jumper grasped his/her re-
aerodynamics and reducing control for the jumpers involved. serve parachute (rather than the aircraft door) as he/she exited
During airborne operations involving aircraft with two exit the aircraft. It was assumed that this procedure could have
doors, jumpers exiting the aircraft from opposite doors at the reduced injuries to the upper arm and shoulders, although no
same time could collide as the aircraft slip stream forces them data were provided to support this assumption. 3
together and their parachutes could become entangled (Figure
3). A system called Controlled Alternating Parachute Exit Sys- Parachute Ankle Brace
tem (CAPES) was developed at the 82d Airborne Division.
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CAPES involved simply alternating jumps between the two air- The parachute ankle brace (PAB) is perhaps the best researched
craft doors so that the jumpers exit at slightly different times, item of equipment ever tested for reducing injuries in airborne
reducing the likelihood of entanglements. Data showed that the solders. However, the history of this device shows how an ef-
introduction of CAPES in fiscal year 1980 reduced high-altitude fective injury reduction innovation will not be used if soldiers
entanglements from 0.54/1000 jumps to 0.06/1000 jumps (RR do not accept it and the device is not strongly promoted and
[CAPES/no CAPES] = 0.10, 95% CI = 0.04–0.25). The number institutionalized.
of high altitude and mid-altitude entanglement injuries was re-
duced from 0.13/1000 jumps to 0.02/1000 jumps (RR [CAPES/ Studies in the sports medicine literature indicated that prophy-
no CAPES] = 0.16, 95% CI = 0.04–0.72). In summary, CAPES lactic ankle bracing could substantially reduce the incidence
17
substantially reduced entanglements and entanglement injuries. of ankle injuries. 20–22 The US Army worked with Aircast Cor-
poration (now DJOrtho) to design the outside the boot PAB
Early in the development of aircraft exit procedures, jumpers shown in Figure 3. An initial study conducted at the US Army
were instructed to grasp both sides of the door as they exited Airborne School in 1993 showed that those wearing the PAB
the aircraft. This created a situation where the static line could tended to have a lower incidence of inversion ankle sprains
be in front of the jumper’s outstretched arm (Figure 4). If this (3.8/1000 jumps vs 0.5/1000 jumps, p = .04). In 1994, the US
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