Aerial Firefighting Involves Heat, Smoke And Turbulence, Part 1

While panicked residents in a Scottsdale neighborhood scrambled to collect a few valuables and drive haphazardly out of the path of the approaching flames, the first firefighters responding amidst the chaos needed a buffer line to keep the flames from getting to the homes.  Fortunately sitting standby at nearby Phoenix-Mesa Gateway Airport (KIWA) in Arizona were air tankers poised to leap into action.  

The first air tanker on scene was “Tanker 167,” an Avro RJ85 operated by AeroFlite. The incident commander instructed the tanker crew to “paint” a group of houses on the boundary of the suburb with their load of retardant. This is a rare instruction, but it illustrated the desperation of the rapidly evolving situation. Next in line was a massive DC-10 operated by 10 Tanker which dropped a long line of retardant, then was instructed to “load and return” to the tanker base at KIWA.

Air tankers pounded the fire line for the next two days as 300 firefighters from multiple local, state and federal agencies bravely stood between the flames and the neighborhood in searing heat. Nearly 3,000 acres were charred and 1,100 people evacuated during the two-day battle. Despite the formidable challenges, no homes were lost, and some of the grateful residents are proudly showing off the new pink tint on their fences and roofs left by the retardant.
  
While these aerial firefighters should have taken a few moments to see the relief and joy in residents who faced losing all of their dreams, the wildfire season doesn’t allow such a luxury. The air crews were already on their way to other wildfires in the west, living the life of vagabonds.  Each morning they put their overnight bags in the aircraft, not knowing where they will sleep that night. This routine will continue day after day until the wildfire activity subsides with winter’s snow.

Variety of Fixed-Wing Missions

A wide variety of fixed-wing and rotary-wing aircraft are used for aerial firefighting. Our recent article on situational awareness described the immense challenges for a helicopter pilot with a water bucket suspended from a long line over a fire incident. This article will focus more on the fixed-wing assets.

Their distinctive calls signify their mission. “Jumper 42” (pronounced four-two) was the call sign I had the privilege of using for several years while piloting the Basler conversion of the DC-3 that flew smokejumpers out of McCall, Idaho. We would use that call sign both when communicating with other firefighting assets as well as with ATC to signify that we were a smokejumper aircraft.
  
“Lead” is the call sign for a lead airplane. The lead plane pilot typically begins an initial survey of the immediate fire vicinity, evaluating the fire’s behavior, fuel type (grass, shrubs, trees, etc.) and topography to determine the optimal use of retardant for slowing a fire’s growth, as well as the surrounding terrain to determine the best approach and exit routes from which the heavily-laden and less maneuverable air tankers can drop retardant. Lead planes will often precede an air tanker into the drop zone to indicate exactly where a drop should be made.  

After the retardant drop it is common for a lead plane pilot to subsequently evaluate the accuracy and effectiveness of each drop. Currently the Beechcraft King Air and the Twin Commander 690 are used in the lead plane role in the U.S.

The airspace over a wildfire incident is no place for a haphazard gaggle of aircraft, thus it is common over busy wildfires to use an Air Tactical Group Supervisor (ATGS), or simply called “Air Attack.”  It is usually a fixed-wing airplane staffed with a pilot and a specialized Air Attack Group Supervisor. The Air Attack orbits at an altitude above other resources assigned to the fire and supervises the process of attacking the wildfire from the air, directing fixed-wing airt ankers, helicopters and any other aviation resources assigned to the fire. The Air Attack also coordinates with the ground incident commander to optimize, when possible, the usage of the aerial resources as well as to assure the safety of the hard-working ground resources who are right in the face of the flames.  

“Tanker” is the call sign for the fixed-wing airplanes that drop retardant or water. The smallest is the Air Tractor AT-802 turboprop. This Single Engine Air Tanker, called a SEAT, carries 807 U.S. gal. of retardant. It can operate from general aviation airports with modest runway lengths, thus there are many locations in the west where SEATs are pre-positioned along with the necessary infrastructure to include a mixing vat and storage tanks for the retardant. Their relative maneuverability means that they can build a winding line of retardant in undulating terrain.

The primary disadvantage is the somewhat limited size of a SEAT’s hopper tanks. The AT-802F Fire Boss version is equipped with amphibious floats that are capable of scooping water from lakes.
  
On the opposite end of the tanker spectrum is the Very Large Air Tanker category. The massive DC-10 carries an impressive 12,000 gal. of retardant. The DC-10 is a beautiful site for firefighters on the ground, especially when a long line of retardant is needed. Within a single day the DC-10 air tanker is often dispatched to fires in many distant states due to its speed and weight capabilities.
        
Thin Safety Margins
The special retardant is a heavy mixture of compounds purposely designed to slow a wildfire’s intensity and rate of spread, allowing firefighters to construct fire line safely. The retardant is tinted with a red dye that enables flight crews to see where previous retardant has fallen.  This is especially needed when the goal is to extend a line of retardant with subsequent drops. 

To optimize its efficiency, retardant needs to be dropped within a limited band of altitude and airspeed. This envelope is close to the slow-speed maneuvering margins of these aircraft. The “low and slow” maneuvering shaves the safety margins. The maneuvering required around the undulating topography of wildfire-prone terrain the western U.S. makes it especially challenging for an air tanker pilot to keep the aircraft within these limits. The safety margins are quickly dwindled when combined with other factors such as unpredicted tailwind shifts.

Sometimes the ferocity of a flame front is so intense that firefighters on the ground literally need a drop of retardant mere yards away. However, the possibility of injury to ground fire crews if inadvertently struck by the weight and velocity of retardant is considerable. Similar precautions are necessary when dropping para-cargo to smokejumper crews. This requires precision from the flight crews and close coordination between ground and aerial resources.

In part 2 of this article, we describe how atmospheric turbulence and pilot-commanded maneuvering can lead to accelerated metal fatigue in aircraft.