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causing the pilot chute to release. Most older models use a mechanical or pyrotechnic pin pulling technique. Newer models use a pyrotechnic loop cutting design. 

For many years, AADs were primarily used by the military and student parachutists. The designs were bulky, expensive, and, to a degree, inconsistent. The installations themselves were cumbersome and awkward. In the early 1990s, a new generation of AADs became available. The CYbernetic Parachute RElease System (CYPRES $^{®}$) uses modern parachute release technology. It is small, reliable, computer based, and uses a pyrotechnic loop cutter. It has an auto-off feature that turns the unit off after 14 hours of operation to conserve power. It also has the ability to calibrate the unit for operation at altitudes other than the calibrating ground level. Based on these concepts, other companies have developed similar systems and as a result, changed the approach to the design and use of AADs. Today, a good many sport parachutists use an AAD and some countries (rightly or wrongly), mandate their use by all parachutists. 

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The following describes the operation and installation requirements of the CYPRES$^{®}$ model AA. Other designs, such as the Vigil$^{®}$, are compatible with these installation requirements. 

## Operation 

The CYPRES$^{®}$ system is a barometrically controlled microprocessor that activates a pyrotechnic cutter that cuts the container locking loop. When calibrated to ground level, the barometric sensor activates the unit firing the cutter when the descending parachutist reaches an altitude of approximately 750 feet above ground level (AGL) and exceeds a rate of descent of 115 feet per second (fps). 

The CYPRES$^{®}$ consists of three parts: 

1. Battery and processing unit 

2. Control unit 

3. Cutter  [Figure 2-45] 

