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W. David Wardall
07/31/2014 11:36 AM

This open letter is for the person who flew an unmanned aerial vehicle through the Sand Fire. I retired from CAL FIRE in 2008, after 31 years as one of the aviation managers, aerospace engineering and aircraft maintenance. I also flew tankers. A medium-sized, four-pound bird can destroy a turbine engine. The bird parts ingested by the engine will block air paths and over-temp the engine. It costs $150,000 to $500,000 to remove and overhaul a turbine engine. This would hold true if the engine hit and ingested the UAV, too.

Now, a hard metal UAV with a hard battery. A hit by an air tanker would do a lot of damage to a wing or tail flight control surface. If the pilot survives this mid-air collision, and the aircraft can make it back to the airport, the tanker will be out of service while an engineering assessment is made and repair plans produced and materials ordered to make a structural repair. A prop strike would cost $60,000, plus anytime a prop is replaced due to a strike, you have to overhaul the engine, too.

A helicopter hit on the main rotor blade is around $110,000 for the blade, plus shop time to replace the blade and rebalance the rotor system. The real danger hitting a helicopter is the main rotor control tubes and linkage. Due to critical weight considerations, these are very light-weight aluminum tubes. They do their job, but a hit of even two or three pounds on these tubes would result in the immediate loss of the helicopter.

I hope the FBI, County Sheriff, FAA and CAL FIRE law enforcement pursue and arrest this person. It’s tough enough to fly in smoke-filled skies with severe up/down drafts, watching for other firefighting aircraft and firefighters on the ground. A pilot does not have the time to search for a UAV and it is so small at 200 mph, he/she will not see the UAV.

W. David Wardall

Deputy Chief, Ret.

Aerospace Engineering & Maintenance

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