Appendix G requires a launch operator to wait for specified amounts of time after a lightning strike or when launch would take a flight path too close to an electrified cloud.

More Leeway Given for Unmanned Rocket Launches

A new direct final rule from the Federal Aviation Administration adjusts its 2006 lightning requirements for expendable launch vehicles to match changes adopted by the U.S. Air Force, increasing launch availability.

The criteria in place for the past five years guiding the launch decision for unmanned rockets that deliver satellites into orbit are being revised by the Federal Aviation Administration. FAA has published a direct final rule to adjust its 2006 requirements to avoid natural and triggered lightning during flight -- including Appendix G, which requires a launch operator to wait to initiate a flight for specified amounts of time after a lightning strike or when launch would take a flight path too close to an electrified cloud.

Appendix G was based on recommendations developed by a Lightning Advisory Panel to NASA and the U.S. Air Force.

Now, FAA is expanding the applicability of certain exceptions "and recognizing that the risk of triggering lightning is less than previously understood at distances closer than previously believed," the rule states. It is codifying criteria for obtaining accurate radar reflectivity measurements to ensure calculation of the volume-averaged, height-integrated radar reflectivity and other measurements, such as the vertical extent of a cloud top, represent actual conditions at the time of launch, because those calculations are instrumental in determining the presence of and risk posed by electrified clouds, it says.

The requirements will continue to state that a launch take place only when it is clear that all criteria, including Appendix G's lightning flight commit criteria, are satisfied. "In other words, each paragraph of each section must be individually satisfied at the time of launch," the rule states. "In short, the burden is on the launch operator to ensure that conditions are safe for launch."

The rule takes effect July 25, 2011; comments are being accepted until July 8 (, Docket Number FAA-2011-0181).

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