nlappos hit the nail on the head. In addition to the publication he suggests....Read pubs by Ray Prouty or try to contact him via email...I think he writes for Rotor&Wing again.
Multi-Axis Airbag system may be useful in a "low G" impact...But most helicopter crashes involve "high G" loads that an airbag would do little or nothing to improve survivability. A good "5-point harness" is the way to go with other attenuation devices (ie seat stroke, "rollbar" airframe design....)
