BASE Jumping - Comparison With Skydiving

Comparison With Skydiving

BASE jumping grew out of skydiving. BASE jumps are generally made from much lower altitudes than skydives, and a BASE jump takes place close to the object serving as the jump platform. Because BASE jumps generally entail slower airspeeds than typical skydives (due to the limited altitude), a BASE jumper rarely achieves terminal velocity. Because higher airspeeds enable jumpers more aerodynamic control of their bodies, as well as more positive and quick parachute openings, the longer the delay, the better.

Skydivers use the air flow to stabilize their position, allowing the parachute to deploy cleanly. BASE jumpers, falling at lower speeds, have less aerodynamic control, and may tumble. The attitude of the body at the moment of jumping determines the stability of flight in the first few seconds, before sufficient airspeed has built up to enable aerodynamic stability. On low BASE jumps, parachute deployment takes place during this early phase of flight, so if a poor "launch" leads into a tumble, the jumper may not be able to correct this before the opening. If the parachute is deployed while the jumper is tumbling, there is a high risk of entanglement or malfunction. The jumper may also not be facing the right direction. Such an off-heading opening is not as problematic in skydiving, but an off-heading opening that results in object strike has caused many serious injuries and deaths in BASE jumping.

At an altitude of 600m (2,000 feet), having been in free-fall for at least 300m (1,000 feet), the jumper is falling at approximately 55 m/s (190 km/h, 120 mph), and is approximately 10.9 seconds from the ground. Most BASE jumps are made from less than 600m (2,000 feet). For example, a BASE jump from a 150m (500 foot) object is about 5.6 seconds from the ground if the jumper remains in free fall. On a BASE jump, the parachute must open at about half the airspeed of a similar skydive, and more quickly (in a shorter distance fallen). Standard skydiving parachute systems are not designed for this situation, so BASE jumpers often use specially designed harnesses and parachute containers, with extra large pilot chutes, and many jump with only one parachute, since there would be little time to utilize a reserve parachute. If modified, by removing the bag and slider, stowing the lines in a tail pocket, and fitting a large pilot chute, standard skydiving gear can be used for lower BASE jumps, but is then prone to kinds of malfunction that are rare in normal skydiving (such as "line-overs" and broken lines).

Another risk is that most BASE jumping venues have very small areas in which to land. A beginner skydiver, after parachute deployment, may have a three minute or more parachute ride to the ground. A BASE jump from 150m (500 foot) will have a parachute ride of only 10 to 15 seconds.

One way to make a parachute open very quickly is to use a static line or direct bag. These devices form an attachment between the parachute and the jump platform, which stretches out the parachute and suspension lines as the jumper falls, before separating and allowing the parachute to inflate. This method enables the very lowest jumps (below 60m / 200 ft) to be made, although most BASE jumpers are more motivated to make higher jumps involving free fall. This method is similar to the paratrooper's deployment system, also called a PCA (Pilot Chute Assist).