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Design for Inspection (Aviation Norms and AWE)

Aircraft are sensitive fragile objects and even a small bump by ground equipment or a wayward mud-dauber nest in a pitot-tube can cause a crash. Aircraft are typically inspected before each flight by at least a walk-around Pre-Flight Inspection. NASA even learned by tragedy to "Pre-Flight" the shuttle carefully in space before re-entry. By tradition aircraft are given an intensive 100-hr (flight hours) Inspection. and a rigorous Annual Inspection that "takes the plane apart" to visually inspect every nook and cranny. The trend in commercial aviation is to make inspection more flexible by squeezing sub-inspections into busy working schedules to reduce downtime. Sensors are increasingly relied on to detect fault conditions. Many aircraft mechanics and owners have varying certification to perform limited inspections, with FAA Inspectors at the top of the inspection hierarchy. The system works well enough that accidents due to maintenance errors and inspection lapse are rare, but extreme vigilance is an ongoing requirement.

We read many claims about utility-scale AWE aerial platforms that will operate by themselves for even a year at a time. Its true that space probes are designed for this sort of duty, but at fabulous expense and in very limited numbers, with many failures overall. Despite some harsh environmental factors, in many ways space is less dynamic and dangerous than unattended operation on earth. Even nesting birds are a factor and special cases like VTOL flight will throw gravel at high speed and sandblast surfaces. We have to conclude that the loudest claims for economically attainable acceptable reliability of complex AWE platforms are dubious.

We should accept the pre-flight/100-hr inspection tradition as the initial default, especially if we seek early FAA acceptance. Visual preflight inspection might be done by cameras, with fault sensors relied on for certain critical functions. The hundred-hour inspection standard will require a human for all platforms of standard aircraft construction. Even the most optimistic AWE claimants predict a rigorous "Annual", which entails at least a few days downtime, likely in a hangar.

There are some ways to avoid the worst impacts of the inspection reality. Smaller, lower-mass, lower-speed platforms have a lowered inspection requirement due to lower consequence of mishaps. Redundant critical features (like KiteGen's case for double tethers) also relax the inspection need. Simplicity and easy inspectability really help. While soft kites, especially the single-skin versions, are not the hottest wing in the sky, they clearly are the most inspectable and repairable by easily trained certified parachute riggers in the field.

CoolIP                       ~Dave Santos             Jan. 20, 2010              M2950


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