Most pilots are well aware of the hazards of hitting trees, but last weekend several firefighting aircrews reported that they narrowly missed being struck by large branches at altitude. Britt Coulson of British Columbia, Canada-based Coulson Aviation told the San Francisco Chronicle that aircraft battling the Washburn Fire in Yosemite National Park reported branches and other debris swept high enough by convective currents that it dropped in clear view of the company’s aircraft, even striking the fuselage of one waterbomber, according to the paper.
The pilot of a lead King Air posted this radio transmission on Twitter: “Hey, just want to let you know a branch went right over the top of us, pretty good size, probably 50 feet above us coming down and fell right in between Tanker 103 and myself.”
In a wildfire, convection is caused when cool air replaces rising hot air. The inflow at ground level creates an updraft that can be strong enough to generate a “reverse tornado,” carrying debris high into the sky. Coulson said, “There is a lot of stuff the convective air around a fire can bring up.”