By Richard L. Hilderbrand
EARLY SPRAY EQUIPMENT
Military aircraft have long been used to apply insecticides and herbicides. An entomologist from Cleveland, C. R. Neillie, believing that airplanes could be used to dust a stand of trees, worked with the Army Air Service at McCook Field in Dayton to test the idea. On August 3, 1921, Lt. John A. Macready assisted in the successful treatment of catalpa trees using insecticide dropped from a Curtiss JN-6 airplane to kill sphinx caterpillars.
In 1933 a study summarized the military use of chemicals dispersed by aircraft and included the possibility of using chemicals to deny the opposition the use of rear areas and lines of communication. This basic idea was applied in Vietnam to deny cover and limit food crops.
An engineering study completed in 1952 laid the groundwork for the development of the MC-I “Hourglass” system which was first used for defoliation in Vietnam. Built by the Hayes Aircraft Corporation of Birmingham, AL, the MC-1 system included a 1,000-gallon tank and equipment to support six spray nozzles.
The MC-1 was used on many occasions but was not satisfactory to spray jungle foliage in Vietnam in “Operation Ranch Hand” due to the requirement for two passes over the treatment area. Knowing a second pass was coming for adequate treatment allowed the enemy on the ground to prepare a “return” welcome party. On February 2, 1962, Ranch Hand lost an aircraft and the crew became the first Air Force fatalities in Vietnam.
The need for a three gallon/acre spray capability in one pass resulted in the development in 1966 of the A/A45Y-1 sprayer which incorporated spray booms under each wing and under the tail and a larger pump to increase pressure from 38 to 60 psi. The A/A45Y-1 Internal Defoliant Dispenser, also designed and manufactured by Hayes, was a complete dispensing system with a 1000 gallon tank, jettison capability, and rapid installation into and from a C-123.
In the spring of 1953, Douglas Aircraft Company was flying a DC-7 prototype out of Palm Springs Airport using water in a tank as a ballast to represent a load. At the end of flight-testing, the four-engine DC-7 made a low pass over the Palm Springs runway and dumped its ballast through three six-inch valves in the airplane’s belly. The result was a wide, mile-long swath of water that caught the attention of the DC-7’s pilots as well as observers, thus starting the concept of aerial attack on fires. The first application of aerial attack adapted a 1939 Stearman biplane that had been converted into a cropduster. In 1955 Willows Flying Service, a California agriculture chemical applicator, cut a hole in the airplane’s belly fabric and fitted the chemicals hopper with a flapper hatch that opened when the pilot pulled a rope to release 170 gallons of water. In August of that year the Willows Stearman made several runs on a fire burning in Mendocino National Forest, dropping 170 gallons on each run and assisting in “knocking down hotspots.” This was the first time that a real forest fire had been attacked using water dropped from the air.
In 1958 a single engine TBM Avenger (Grumman TBF manufactured by General Motors) dropped retardant on a fire at Lake Elsinore, California and started the use of the TBM as a retardant tanker. Continuing through the 1960s, the tankers were usually modifications of WWII bombers, such as the TBM, that carried a several hundred gallons of retardant and dropped the load using the bomb bay. These drops were bulk drops and frequently a mass of retardant would break the trunks of trees. The military bombers were designed to withstand the “negative g” wing-loads of rapid cargo (e.g., bombs) deployment but were not necessarily adapted to the low-level drops in mountain terrain. Other aircraft used were the PB4Y, B-26, B-17, and P2V Neptune. Other military aircraft were used such as the Grumman AF with a payload of 800 gallons and the C-123. They were usually single purpose aircraft owned and operated by private contractors with much time parked on the ramp. These early pilots flew on the edge and would occasionally return to the retardant base with pieces of tree-top in their wings. C-119 “Flying Boxcars” were used through about 1987 and a few even had 3,400-pound-thrust Westinghouse J34 turbojet atop the fuselage.
EMERGENCY LANDING AT A FORD PROVING GROUND
One story from 1979 and recounted by Bill Waldman (Aero Union pilot) concerned a drop he made east of the Colorado River in the Grand Canyon area. He made a partial drop and was pulling up out of the canyon. The C-119 made a drastic roll to the right so the co-pilot was looking at the rocks on the hill through an overhead window. Waldman jettisoned the load, corrected the roll and looked for an emergency landing spot and realized the Ford proving ground south of Kingman, AZ, was the best available. He held the plane level long enough to reach the skidpad test area at the proving ground, clearing the many new Fords on the pad by a few feet. He landed and was met by the manager of the proving ground who told his machine shop staff to give this pilot and plane anything they need to “get off my skidpad.” A 4 x 6 inch piece of aluminum and sheet metal screws repaired the flap and the plane with one dead cylinder due to a swallowed exhaust valve and a make-do patch flew to the canyon airfield for repairs. Over the time of their use three C-119s were lost due to structural failure.
Following the WWII bombers, the DC-4 (C-54), DC-6, DC-7, MD-87 and Lockheed P-3 Orion have been employed. California fire fighting continues use of military aircraft with the Grumman S-2T tanker that can hold about 1,200 gallons of retardant. The S-2T aircraft were used to track submarines until the 1970s.
The use of aerial firefighting aircraft has reached a new peak with the conversion of DC-10 and Boeing 747 aircraft to supertankers capable of carrying thousands of gallons of retardant. The supertankers drop at a few hundred feet or higher at 140 knots but cannot fly at tree top level as did the early pilots. The DC-10 conversions carry a load of 9,400 gallons and the 747 carries 17,500 gallons. The 747 interior contains several tanks that cover much of the length of the interior including the compressed air tanks for dispersal. The volume of retardant dropped is impressive and dispersal improved – the 747 may make a drop covering two to three miles and 100 yards wide.
Water can be used to cool a fire; however, the retardant is usually distributed in a line in front of the fire to assist ground teams with building a line to stop the fire. The retardant is a mixture of fertilizer type material that retains or absorbs moisture, decreases fire intensity and slows advance of the fire (even after drying) and is intended to act as a fire break when the fire reaches the retardant drop line. In 1956 borate was briefly tested on fires in southern California and found to be a soil sterilant but early air tankers were often called “borate bombers.” Today’s retardant is generally an ammonium-phosphate or sulfate based commercial mixture which is colored red to mark the drop site and weighs about nine lbs/gallon. The Monsanto brand Phos-Check became available in 1962. The product PHOS-CHEK® is now trademarked and produced by Perimeter Solutions and is one of a several retardant products. Certain current formulations of retardants can be used to pretreat fuel to act as a retardant and are resistant to weather conditions for extended time periods.
PROGRESS BRINGS PROBLEMS
Jim Hickman has memories of a few incidents from the early development of Modular Aerial Firefighting System (MAFFS) air tankers. When mixed with water, retardant is not only wet but very sticky and slick when coating a surface. In an early trial several hundred gallons of the retardant were loaded into the modules of a C-130 and the test run started. When valves were opened there was a dramatic and immediate dispersal with much of the sticky retardant mist flying back through the open ramp into the interior of the aircraft, where it coated every surface. Fortunately, it did not access the cockpit. Several modifications were completed to improve the filling of the tanks and the placement of dump nozzles to achieve proper dispersal of the retardant.
There were other errors and incidents which occurred with civilian-operated aircraft. One tanker had dual wheels on each main gear and had loaded at the tanker base at Prescott, AZ. The plane taxied out of the retardant pit, turned onto the main runway and took off. In about a minute the dispatcher had a frantic call from a civilian telling them that a huge wheel had just fallen off an airplane, hit on the street, bounced over a house, and was off in the woods. About then a pickup roared up to the tower and one of the retardant crewmen ran in with a handful of debris from the tarmac where the tanker had turned to go onto the main runway. The lead plane pilot watched while the tanker pilot lowered the main gear. Sure enough, the outside dual on one main landing gear was missing. The plane went on to the fire and dropped retardant, diverted back to the home base and made a safe landing. During development, the military pilots had flying experience but no fire suppression experience. In early MAFFS operations the military pilots were having trouble dropping the retardant in the location needed at the fire. As orientation the USAF pilots were flown in civilian tankers with experienced tanker pilots. Upon return from an orientation flight in a B-17 the AF pilot was asked what he thought – his reply, “The SOB was trying to kill me.”
A recent tragedy was the loss of Coulson Aviation’s Tanker 134 (a former Navy C-130) fighting Australia’s bush fires on January 23, 2020. The tanker was outfitted with Coulson’s RADS XXL retardant delivery system capable of dropping 4000 gallons on each run. The three crew members lost were decorated veterans of the U.S. Military services and each had extensive experience. The crash occurred north of the Cooma-Snowy Mountains Airport (near Peak View), New South Wales.
One incident of interest to me concerned a PB4Y2 on a fire in Alaska. I was on the fireline and watched with concern as the pilot came in on the level approaching below a fire but needing to climb up to the fire on the side of a mountain. Normal procedure was to come loaded over a ridge or hilltop and drop retardant going down the slope and then pulling up after the drop and returning to base. The drop was made, the engines roared and the PB4Y2 just cleared the trees on the top of the ridge. The PB4Y2 crashed a few days later July 22, 1968, on Joaquin Mountain in Alaska with the loss of four lives.
In another case a contract C-130A (civilian-operated) aircraft was flying against the Cannon Fire, near Walker, CA, on June 17, 2002, when it experienced a structural failure of the center wing section, causing both wings to fold upward and separate from the aircraft. Two weeks later another contract-operated PB4Y from WWII crashed near Estes Park, CO, also as a result of structural failure. A total of five personnel were killed in the two crashes.
As a result of the accident investigations, on May 10, 2004, the USFS abruptly terminated the contracts for many of the large tankers over safety concerns. The decision affected tanker contracts issued by both the USFS and Bureau of Land Management. In the vacuum left by the absence of the large tankers, the Forest Service said it would shift its firefighting strategies to rely more on heavy helicopters, light tankers and military MAFFS. With improvement of safety procedures the strategy has changed and the large aircraft, including supertankers, are currently operating world-wide.
The article was edited to show that the TBM was manufactured by General Motors, not Ford.
Richard Hilderbrand, Ph.D., was a Smokejumper in the mid 1960’s and is a Life Member of the National Smokejumper Association. He was on fires in the Northwest US and Alaska. He has personally seen TBM aircraft return with tops of trees in their wings and has seen retardant drops from many aircraft. He has jumped from a Ford Tri-motor, DC-2, DC-3, Twin Beech, Grumman Goose and other jump aircraft. Special thanks are due to Jim Hickman, Bill Ruskin, Bill Allred, Bill Waldman, Bill Gabbert, and Steve Whitby for their contributions and review! In addition, I thank the many websites referenced in the text for their information; however, any errors are the responsibility of the author.