HALO
Acronym of high altitude, low opening (“a type of skydiving where one leaves the launch platform from a high altitude and opens the parachute at a very low altitude”).
HALO: extreme altitude jump with late parachute deployment
HALO stands for high altitude, low opening, a skydiving technique where the jumper exits an aircraft at 25,000 feet or higher but delays parachute deployment until 5,000 feet or lower. This creates a long freefall period, sometimes lasting several minutes depending on exit altitude and body position. The method is used primarily by military special operations units for tactical insertion, allowing teams to depart from aircraft at altitudes where radar and visual detection are minimal, then navigate horizontally under canopy for ground insertion.
The equipment differs materially from civilian sport skydiving rigs. Jumpers wear pressurized suits or supplemental oxygen systems because the thin air at 25,000 plus feet causes rapid oxygen depletion and hypothermia. A primary parachute rated for deployment at altitude, typically a ram-air canopy of 400 to 500 square feet, is paired with an emergency reserve. Altimeters with audible warning systems are essential, as jumpers must deploy before reaching unsurvivable altitudes. Specialized helmets with integrated oxygen delivery and communications equipment are standard. Exit procedures require stable body positioning to minimize tumbling during the high-altitude phase.
Hazards and operational limits
Hypoxia is the primary physiological risk. Without supplemental oxygen, useful consciousness is lost in minutes at these altitudes; even with oxygen systems, equipment failure is catastrophic. Canopy deployment shock loads the body harder from higher forward airspeed, requiring experienced jumpers and well-maintained equipment. Weather becomes critical: jet stream winds aloft can push teams miles off intended landing zones, and temperature inversions affect freefall rate and canopy performance.
The term emerged in military aviation during the 1960s as special operations forces sought low-signature insertion methods. It contrasts with HAHO (high altitude, high opening), where the parachute deploys immediately after exit, allowing navigation under canopy from high altitude. HALO requires greater technical skill, better equipment conditioning, and higher risk tolerance than HAHO, making it the choice when stealth during descent is paramount rather than horizontal range.