Page 112 - JSOM Winter 2019

Lord and Coutts complied data from the US Army Parachute and both had a very severe opening shock. By the end of the
4,5
School at Fort Benning, GA, from April through December war, the T-7 had been modified to have a single point release
1943. As shown in Figure 1, the overall incidence of injuries system that could easily collapse the parachute canopy once
declined during this period. Injuries were defined as any con- the jumper had landed. All early parachutes had 28-foot flat
dition resulting from training that caused the trainee to lose ≥1 circular canopies (when inflated) with 22-foot (T-4 and T-5)
day of training and involved both training and jump injuries. or 24-foot (later T-5 and T-7) diameter reserve parachutes.
The authors largely credit the decline in injury incidence to The T-4, T-5, and T-7 were all canopy first opening systems,
revisions in landing techniques, which were an early version although it was generally understood that a safer system with
of the PLF. In one revision, the trainee was taught to hold his less opening shock might be devised by having the canopy ris-
feet together, slightly bend his legs, and place the body weight ers (canopy suspension lines) deploy first. Canopy deployment
slightly forward over the legs before ground contact. The sec- with all these early parachutes could be erratic depending on
ond revision involved approaches in which the wind forced the winds and the aircraft slip stream. 6,7
jumper into a backward or oblique approach in which case a
tumbling technique was taught. These revisions were intro- In 1952, the T-10 began to replace the T-7, and by 1954, the
duced in June 1943. T-10 implementation by the US Army was completed. The
T-10 served as the main US Army personnel parachute system
FIGURE 1 Injury incidence at the US Army Parachute School, for >50 years (between 1954 and 2010). With the T-10 the
4,5
Fort Benning, GA, 1943. (Data estimated from Lord and Coutts. )
risers came out first, followed by the canopy. This allowed
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jumpers to fall below the aircraft slip stream before the canopy
deployed and this reduced the opening shock. The T-10 system
had a 26-foot inflated parabolic canopy and a total weight of
44 lb and was rated for a maximum load (jumper and equip-
ment) of 350 lb. This parachute was designed and developed
when the estimated average load of the soldier and his equip-
ment was about 300 lb. However, soldier body weights and
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combat loads progressively increased since the 1950s. 8,10,11
One study of 624 Rangers who jumped into Panama during
Operation Just Cause (19 December 1989) found that 24
(4%) carried loads that exceeded the maximum allowable.
8
During airborne operations in Afghanistan in 2001 and in Iraq
in 2003, average loads ranged from 327 to 380 lb. 12
The need for a new parachute system to accommodate the
greater Soldier loads was recognized in 1994 and work be-
It is likely that the introduction of the PLF did not totally ac- tween this time and 2010 lead to the development and imple-
count for the decline in injury rates seen in Figure 1. Tobin mentation of the T-11 Advanced Tactical Parachute System.
et al. examined causes of injuries at the US Army Airborne The T-11’s rate of descent was 19 ft/sec (5.8 m/sec), compared
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School in the first year of operations. They noted that training with the T-10’s rate of 22 ft/sec (6.7 m/sec). Crude estimates of
involved practice jumps from 4-, 6-, and 11-foot platforms the kinetic energy (KE = ½ mass × velocity ) on ground impact
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and that the 11-foot platform was eliminated because of a for the two parachute systems are given in Table 1. Because
high injury rate. They also credit a decline in injuries to in- of its shape (modified cruciform), the T-11 oscillations are
tensive ground training prior to actual jumping, although they highly dampened and the parachute becomes vertically stable
did not provide data to support this. During the decline in in- very soon after deployment. 9,13 The T-11 reserve parachute has
juries seen in Figure 1, Lord and Coutts give credit not only characteristics similar to the main parachute, and the aerody-
4,5
to the introduction of the PLF but also to better supervision of namics are such that if both the main and reserve parachutes
students by instructors and improved maintenance of equip- are deployed, they do not interfere with each other. However,
ment and training aids. Also, note in Figure 1 that injuries because of the large canopy, the T-11 likely has more lateral
were declining prior to introduction of the PLF in June 1943. drift, less free air space on mass tactical jumps, and a greater
drag hazard once the jumper is on the ground. Figure 2 shows
the T-10 and T-11 parachutes.
Parachute Systems
One of the major improvements in airborne operations has TABLE 1 Estimates of the Kinetic Energy of the T-10 and T-11
been developments in parachute technology. Military para- Parachutes on Ground Impact
chutes designed for intentional jumps from aircrafts were Soldier Mass Velocity Kinetic Energy
designed as “T”-type parachutes, with the “T” understood Parachute (kg) (m/sec) (J)
to mean “troop” by mid-World War II. The first parachute T-10 80 6.7 1796
actually used by the soldiers of first US Army airborne test T-11 80 5.8 1346
platoon in 1941 was the T-4. The T-4 system was designed as *Kinetic energy = ½ mass × velocity .
2
a ripcord parachute but it was modified by the test unit for
static line deployment. The T-4 had a 15-foot static line and Two major studies compared injury rates of the T10 and T11
a pack tray that did not totally encompass the parachute can- parachutes. One study was conducted at the US Army Air-
opy and was difficult to don and doff. The T-4 was followed borne School, and the other was in operational unit train-
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by the T-5, which was designed from the start for static line ing. The Airborne School study involved trainees who
14
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deployment. The T-5 and T-7 were used during World War II, performed their first jump with the T-11. Only the safer
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110 | JSOM Volume 19, Edition 4 / Winter 2019