AAD Activation Altitude

Q:

 

Should I consider adjusting the activation altitude of my automatic activation device?

 

A:There are several modern AADs available for skydivers to choose from, all of which offer jumpers the ability to offset the activation altitude (temporarily change the activation-altitude settings to compensate for a landing area that is higher or lower than the point of departure). Additionally, both the Airtec CYPRES 2 and the Advanced Aerospace Designs Vigil 2+ offer a feature that allows users to increase the activation altitude semi-permanently (until the user changes it again).

In January 2013, Airtec began shipping its CYPRES 2 AAD with a feature that allows the user to increase the activation altitude from the standard 750 feet up to as high as 1,650 feet, in 100-foot increments. On April 10 of this year, Advanced Aerospace Designs announced that by the end of April it would introduce a version of its Vigil II, the Vigil 2+, on which users can adjust the activation altitude. Considering that there have been at least nine fatal accidents in which AADs activated at their designed firing altitudes but the reserve parachutes did not fully inflate before the jumpers struck the ground, the introduction of user-adjustable altitude settings could be a good thing. The Parachute Industry Association continues to investigate the delayed reserve inflations, and although it has not yet found a single determining factor to be the cause of the fatal accidents, in each, an additional 200-300 feet of altitude may have allowed the reserve to fully inflate in time to save the jumper.

If you do decide to bump up your AAD’s activation altitude, you’ll also need to keep your main deployment altitude in mind. Airtec warns users to plan to have an open main canopy at least 1,000 feet above the CYPRES activation altitude to reduce the chances of experiencing a dual deployment of the main and reserve canopy. This means that if you bump the unit’s activation altitude up 300 feet (to 1,050 feet) and your canopy takes 800 feet to fully deploy, to have an open main canopy 1,000 feet above activation altitude means you’ll need to begin your pull sequence by a bare minimum of 2,850 feet. Bear in mind that activation altitudes may not be exact—AADs may fire 300 feet or more above the set altitude depending on the jumper’s body position at activation time.

The CYPRES AAD owner’s manual clearly explains the steps you’ll need to take to increase the activation altitude. At press time, Advanced Aerospace Designs was still developing the instructions for making this change on Vigil 2+ units. For both AAD models, once the user changes the activation altitude, the unit will retain that programming until the user manually changes it again. The altitude adjustment will remain in place even if the unit turns off and back on again.

Don’t confuse increasing your AAD’s normal activation altitude with the feature that allows you to offset an altitude (i.e., temporarily change the activation altitude) for those times when you take off from one location and land in another location at a different altitude. Each AAD manufacturer provides detailed instructions for programming an offset altitude, but that offset will remain programmed in the unit only until it is switched off. And depending on how accurately the estimated offset altitude matches the actual landing altitude, you may need to make changes after landing to ensure it is set correctly for the next jump. The owner’s manuals also explain this process in detail.

Another factor to consider is the altitude of your drop zone. In order for your AAD to calibrate properly for jumps that involve taking off and landing at the same location, it must be switched on at that location. The AAD will use that location’s altitude while it is calibrating during the start-up process to determine ground level. If you turn on your AAD while you are located at your sea-level home and drive to a drop zone at a higher altitude, the AAD will use the altitude where it was turned on (in this case, sea level) as the assumed ground level for your jump. In this example, if you jump at a DZ 1,500 feet higher than where you switched on your AAD, you would never reach its activation altitude. If you did not deploy your parachute, your AAD would not fire before you struck the ground because it would think that the ground was 1,500 feet lower.

Also, if your drop zone is surrounded by higher terrain, your AAD will not account for this. For example, if you are in freefall above a 500-foot hill next to the drop zone, your AAD will assume you are in freefall above the spot where you turned it on (which is 500 feet lower). So, any rising terrain around your drop zone will reduce the time and distance available for your reserve to inflate following activation of the AAD. This might be another situation that warrants bumping up the activation altitude.

Your AAD is an amazing device, but it is not foolproof. A better understanding of its operation and limitations can help you decide what settings will work best for your situation.

—Jim Crouch | D-16979
USPA Director of Safety & Training and FAA Senior Rigger

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