SSK Industries, Inc.

Expert CYPRES in Descending Aircraft

September, 1994 - Cliff Schmucker, SSK Industries, Inc.

Recently there have been a number of reports of skydivers concerned about turning their Expert CYPRES units off when descending in aircraft. One such report came from the Convention at Quincy where a skydiver "panicked" when a Casa load descended due to cloud cover.

The Expert CYPRES activates when a velocity of 35 meter/second (115 feet/sec., 6890 feet/min.) or greater is obtained at an altitude of 750 feet with a skydiver in freefall stable face-to-earth, or tumbling. With a skydiver falling perfectly stable back-to-earth, or with CYPRES in a test chamber, or in a descending aircraft, the activation altitude is approximately 1050 feet. (This 300 ft. difference is due to the low pressure area aft of a freefalling body versus the actual air pressure.)

At the 1994 Richmond Boogie, an Expert CYPRES was placed in Mike Mullins' King Air, as a test to see if their typical descent patterns would activate the unit, even when descending with no skydivers on board.

As expected, the unit

did not activate.

When questioned about standard jump aircraft procedures, Mike Mullins explained that they (West Tennessee Skydiving's King Air) "typically descend at 6500 feet per minute", but by 1000 feet have already "pulled out of the dive".

Hopefully this simple test will help reassure skydivers that there is no need to turn their Expert CYPRES off in this situation. It was designed to accommodate this exact circumstance, thus there is no reason that the Control Unit (the portion with the display/switch) need be accessible to the user when the rig is worn. (The fact is, if you are descending in an aircraft at that velocity at approximately 1000 feet, your CYPRES firing is the last of your worries.)

Note: A Tandem CYPRES activates at 6890 feet per minute at approximately 1900 feet AGL; this still should not be a problem. However, you might want to ask your pilot to take it easy a little higher when riding the King Air or equivalent down with your Tandem student anyway! The Student CYPRES activates at approximately 1050 feet when the velocity is greater than 13 meters/second (43 feet/second, 2560 ft/min) and at 750 feet when the velocity is 35 meters/second (115 feet/second, 6890 feet/min). Thus the Student CYPRES should always be switched off when riding any aircraft down, that is why the Control Unit is often mounted in front of the rig on Student gear, to make it more accessible to the jumpmaster.

SSK Industries is the U.S. CYPRES Service Representative.