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High-Altitude Airdrop Missions [HAAMS]
High Altitude-Low Opening (HALO)
High Altitude-High Opening (HAHO)
[source: http://www.globalsecurity.org/military/ops/airborne-halo-haho.htm]High-Altitude Airdrop Missions [HAAMS] for special assignment airlift missions [SAAMS], often top-secret and clandestine affairs, carry elite troops from every branch of the service - Army Rangers and special forces, Marine recon forces, Navy SEAL teams and Air Force special tactics units.
Jumpers from all services parachute at altitudes up to 35,000 feet with all of the accompanying hazards. High glide ratio parachutes (HGRP) utilize high altitude-low opening (HALO) and high altitude-high opening (HAHO) techniques during day and night operations and under all weather conditions.
The HALO techniques are used for missions to prevent detection of the aircraft and the jumpers. Extreme accuracy is required since the parachutes are deployed at a low altitude. HALO involves paratroopers jumping at around 25,000 feet and freefalling down to 3,500 feet. Plummeting at a terminal velocity of 126 mph, parachutists can descend this distance within two minutes. A HALO jump gets the jumper out of sight in a hurry, and they are less vulnerable to dangers. A drawback to this technique is that the jumpers must exit the aircraft over, or close to, enemy territory, thus making the aircraft a potential target for enemy surface-to-air or air-to-air defenses.
The HAHO techniques are used for missions which require minimal detection of the aircraft under conditions which restrict the aircraft from penetrating a certain area, such as the border of a country. The jumpers will deploy the parachutes at very high altitudes which allow them to glide a considerable horizontal distance with a low probability of detection. Jumpers are consequently exposed to hypoxia and cold temperatures for extended periods. A HAHO is a high-altitude, high-opening jump used for long-range insertion.
During high-altitude, high-opening missions both exit and deployment altitudes are high, and a special parachute lets them maneuver more than 50 kilometers as they quietly float into an area. HAHO allows the jump aircraft to deliver its cargo from a significant standoff range, thereby reducing the odds of enemy detection and increasing the survivability of the aircraft and the parachutists.
The higher the parachute-opening altitude and the flatter the glide slope of the parachute, the greater the standoff distance attainable. Paratroopers hop and pop their 'chutes immediately, which is potentially a riskier maneuver because jumpers are exposed to altitude and the enemy for a longer period. The opening shock is also traumatic. It gives quite a jolt. Jumpers are sore for a few days after a HAHO.
Given the same size parachutes, a heavier parachutist will descend more rapidly than a lighter one. This variable rate of descent is not a problem in low-altitude airborne work; military parachutists traditionally carry their individual combat gear with little regard for weight considerations. However, that approach doesn't work in HAHO operations. Because a HAHO team may travel more than 40 miles under their canopies, a common rate of descent is a critical factor in keeping the team together. To ensure the glide slopes are as uniform as possible, the team's gear is carefully apportioned so that all the team members weigh about the same - heavier troops jump with lighter equipment containers; lighter troops jump with heavier containers. The team's equipment can be redistributed into operational loads after landing.
The most hectic time is from the two-minute warning until the jump. The team is switching over to their oxygen bottles, and you're double- and triple-checking equipment, connections and bottle pressure and watching for symptoms and signs of hypoxia.
The two greatest hazards they must contend with on high-altitude airdrop missions, HAAMS for short, are hypoxia and decompression sickness. Decompression sickness, or the bends, occurs when nitrogen bubbles form in the blood and tissues after a rapid reduction in surrounding pressure. It's manifested by pain in the joints, and is potentially lethal.
Hypoxia is a major concern during both techniques; there is one documented fatality associated with a high altitude jump. Oxygen deprivation causes hypoxia, and its symptoms include dizziness, giddiness, a tingling sensation, euphoria, blurred or tunnel vision, lack of muscle coordination, and slow reaction time. To compensate for the body's craving for oxygen, the heart and breathing rate increases. Hypoxia affects people uniquely, and its symptoms will change with age and lifestyle. That's why all aircrew members are required to go through the altitude chamber regularly. At 10,000 feet, subtle changes take place in the body and these multiply as you go higher. At 35,000 feet, you'll have between 30 to 60 seconds of useful consciousness without supplemental oxygen. Ultimately, this leads to death.
Special Operations Forces regulations define the requirements for safe operation and mission completion. For day operations, supplemental oxygen must be used by all parachutists above 10,000 feet MSL in the aircraft if exposure exceeds 30 minutes. Oxygen is supplied either by inline oxygen or from portable cylinders. If there are extremes in temperature or physical exertion, the jump master can recommend supplemental oxygen at 5,000 feet MSL.
Supplemental oxygen is used during the parachute descent for any jump above 13,000 feet MSL, and can be an option for jumps initiating below 13,000 feet MSL. For night operations, supplemental oxygen is required in the aircraft for all parachutists above 10,000 feet MSL while flying to the drop zone and is encouraged for altitudes above 5,000 feet MSL at the discretion of the jumpmaster. The HALO operations may be performed below 13,000 feet MSL once the parachutist has left the aircraft.
The HAHO operations above 10,000 feet MSL must be performed with supplemental oxygen both in the aircraft and under the parachute canopy. Aircraft oxygen delivery systems must be capable of delivering 100 percent oxygen and supplemental oxygen settings with a mask which conforms to physiologic PRICE check procedures. Parachute canopy oxygen delivery systems such as a simple oxygen cylinder and mask must maintain the jumper's oxygen hemoglobin saturation greater than 92 percent.
The cold is another factor jumpers must contend with. For every 1,000 feet you ascend, you lose 3.6 degrees Fahrenheit in temperature. In those conditions, knowing the wind-chill factor (a function of ambient temperature and wind speed) is important. A parachutist must have manual dexterity for a few minutes before exiting the aircraft to properly adjust the equipment, and immediately after exiting to manipulate the parachute. The parachutists' hands would become extremely cold unless over-gloves are pulled on.
Any time a military flight drops personnel or cargo at altitudes above 18,000 feet, specially trained aerospace physiology technician, nicknamed PTs, must fly on board. These technicians, who are experts in the field of human performance and the effects of flight on the body, monitor the aircrew and parachutists looking for signs of impairment caused by altitude. A physiology tech's most critical duty is recognizing and treating those taken ill by the altitude. They administer to the sick until relieved by a flight surgeon.
In 1995, PTs flew 550 sorties aboard aircraft, including the C-17, C-130, C-141, C-5 and others. They launched from 114 locales, including Pakistan, Australia, Indonesia, Korea, Italy and airfields throughout the United States. Because of the high demand for qualified PTs, the 1st AS is augmented by aerospace PT units at Shaw AFB, S.C.; Little Rock AFB, Ark.; Andrews AFB, Md.; Fairchild AFB, Wash.; Edwards AFB, Calif.; and Kadena Air Base, Japan.
The PT works hand-in-hand with the aircraft commander and jumpmaster. They brief aircrews and parachutists on the hazards of high-altitude operations, and act as an inflight oxygen equipment and physiological consultant. Physiology technicians also repair the oxygen equipment, which include pre-breathing consoles and oxygen bottles strapped to the paratroopers. All receive training from equipment manufacturers so they can troubleshoot and repair malfunctions on the spot.
They regulate the ascent to altitude, directing all on board to "pre-breathe" 100 percent oxygen from a console for a half-hour while holding the aircraft below 10,000 feet. This interval isn't to catch a breather, but to purge nitrogen from the bloodstream, eliminating 90 percent of the cases of decompression sickness. The squadron's aerospace physiology techs, who average six to seven years worth of experience, know Boyle's Law of Gases inside and out. It's one of the basic principles, physics-wise, used to calculate how elevation affects solids, liquids and, most importantly in this instance, gases. It states that PV=k. Pressure and volume are inversely proportional so that when you decrease pressure, volume increases.
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