Douglas A/B-26 Invader

Air Tankers

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The first "air drop" was made on the Mendenhall Fire, August 12, 1955, on the Mendocino National Forest. The first operational air tanker was developed in Willows, by the Willows Flying Service in 1955, at the request of the Fire Control Officer for the Mendocino National Forest. A Boeing Stearman 75 "Caydet" Agricultural Aircraft was modified with a 170 gallon tank at the Willows airport. This Aircraft, N75081, became the first registered free fall air tanker in the history of aviation.

In 1956, seven agricultural aircraft were modified and formed the first operational air tanker squadron in the United States. Piloted by local aviators, this squadron operated out of the Willows Airport fighting wildfires throughout California. Initially, plain water was used as the fire suppressant. However, it was soon discovered that most of the water evaporated before reaching the fire, so the practice was adopted of adding chemicals to the water to inhibit evaporation.

Borate was one of the first chemicals used, hence the derivation of the term "borate bomber."

In 1959, heavy air tankers, capable of carrying 2,000 gallons of fire retardant, were providing an effective tool in controlling wildfires.

.........Enter the A-26 Invader

Ever since N5457V, the first A-26 converted to a fire tanker by Aero Atlas back in 1959, this highly manoeuvrable, single pilot, Ex-WWII attack aircraft has proven its worth in the wildfire theatre of operations, due to its speed, flight duration ( 5 Hours ), Range (1,200 Miles ) and ability to carry a good fire retardent load of 760 US gallons, the A-26 Invader became the mainstay in the battle to deal with the ever growing problem of forrest fires in both Canada and the United States, with some 50-60 A-26 Invader's being converted for Air tanker or drop planes of some or other description, culminating in the ultimate A-26 Air tankers operated by Lynch and modified with STOL capability. 
And to prove the durability of the A-26, N5457V as mentioned above still flies today, owned and operated by David R. Lane.
The first Invaders used for Air Tanker duties comprised of modifications consisting of systems and componants from a variety of othe aircraft of that era.
The basic conversion consisted of installing an aluminum tank with two internal compartments, each having the capacity of 500 + gallons of slurry and their own doors in the bombay, an electrically powered hydraulic system, which was the tail turret hydraulic system removed from a PB4Y-2 and the associated wiring, tubing and controls to operate the tank doors.
In most of the aircraft, the hydraulic panel was located on the starboard side of the cockpit, with the jumpseat removed and which was eventually replaced with a lap belt so a passenger could be carried when required. Just aft of the mainspar, a 1 ft x 3 ft rectangular hole was cut on top of the fuselage for tank venting.
The windbreaking strakes which were mounted just forward of the bombay were removed and in most cases, the opening was not covered. The tanks fitted snuggly in the bombay and extended 2 or 3 inches below the bombay.
The most noticable difference was in the bottom of the tank.
On some tanks, the bottom was flat from side to side, while on others the center line of the tank would be 3 or 4 inches lower than the sides creating a splayed V when viewed from the front.

The list below gives just some of the companies that used the A/B-26 for various Air Tanker and Agricultural spraying duties.
Photos for several of the companies are not available, so a brief history has been inserted whilst a suitable image can be located.

For history and data on individual Invaders throughout the site, I would like to credit the Warbirds Worldwide Directory by John Chapman, thank you John.

Air Tanker companies A - D

Aero Union

Aeroflight Inc

Air Spray

Aircraft Specialties Inc

Butler Aviation

Central Air Service

Central Oregon Aerial Co


Custom Farm Service of Montana (Agricultural)

D & D Aero Spraying Inc. (Agricultural)

Don A. Goodman - Private contractor (Pilot)

DM Air Enterprises Ltd


Dontuss Industries

Air Tanker companies E - J

Evergreen Air

Fire Eaters

Flick Aviation

Flight Enterprises Inc

JD Irving / Forest Patrol Ltd, Saint John

Hamilton Aircraft Co., Tucson, AZ

Thomas W. Hammon - Private contractor (Pilot)

Hawkins & Powers Inc.

Hillcrest Aircraft Co

Idaho Air Tankers Inc

Huitikka Olavi N, Fort Frances

Johnson Flying Service

See the three links below for additional information on aerial firefighting

Type 1. Retardant drop system for A-26 Invader

Type 2. ( Later) Retardant drop system for A-26 Invader

Air Tanker companies K - T


Kenting Aviation

Kern Air Inc

Kinney Air Tankers

Kreitzberg Aviation, Inc

Lynch Flying Service

Mid Canada Aerial Contractors

Mercury Flights Ltd, Edmonton

Moseley Aviation Inc

Reeder Flying Service

Lester Riley - Private contractor (pilot)

Rosenbalm Aviation, INC.

Stahmann Farms Inc. (Agricultural)

George H. Stell - Private contractor (Pilot)

Thompson Flying Service

Associated reading

Ex Air Spray #13 walk round - Dennis Deagle, Edmonton, Alberta

The Lynch STOL 26 configuration

Darcy Hankins - Ex Air Spray engineer

Linc Alexander - Fire Bomber into hell

Dirk Jory - Air tanker pilot

Air Tanker types


How it works
Tankers are used to flank or work parts of a fire to contain it's direction or slow it's rate of spread while ground troops work the fire.
Retardant lines may be used to reduce rate of spread or encourage the fire to move in another direction based on wind, natural barriers, vegetation or types of fuels, topography, slope, aspect (north/south, etc), and of course, threats to persons, structures, etc. Considerations include resources available to back up retardant lines, ground resources, turnaround times, etc.

One of the single most common, and most basic mistakes in retardant application, is to attack the head of the fire, or to go direct on the fire. Without an ability to build line rapidly with short turn-around times or ample air assets, the result is invariably splitting the head of the fire into two or more parts, increasing the rate of spread, and complicating the fire. Most of the time, this only increases fire activity, wastes retardant, and makes the fire worse.

Water cools fire directly, but cooling the fire is the least effective way, and most wasteful way, of controlling it's activity. Unless it's a small spot fire, then water doesn't put the fire out. Water and foam are short term measures, often most effectively used on small spot fires. Where water can be used in extended attack operations, it has to be available in very large quantities, and enough resources need to be present and capable of acting, which can keep a constant application of water on the fire. Scoopers, for example, must have the ability based on proximity of an uplift source, a short distance, and enough scoopers, to keep putting water on the fire every few minutes. Otherwise, the water is usually nearly worthless.

One must remember that in an active wildfire, temperatures above the fuels can exceed two thousand degrees Farenheight, and fuel temperatures and fire activity can mean that water dropped on an active flame front may do little more good than spitting in a camp fire. Water evaporates quickly, any cooling or loss of energy in the fire is quickly replaced and reheated, and the change in relative humidity is so minute that it's negligible in character.

Relative humidity of it's own accord does reduce fire behavior somewhat in intensity and rate of spread, but is a minor consideration compared to winds, slope, fuel moisture, etc.

Fuels on the ground are classed by the amount of hours required to effect a change in fuel moisture. Some fuels such as grass are one-hour fuels, but many fuels over 3" in diameter, like small tree branches, are into the thousand hour range. The introduction of local temporary changes in RH produce insignificant changes in the fire behavior for the most part, and no changes in the fuel moisture. Even a rainstorm only produces brief changes, and doesn't effect fuel moistures save for grasses and other one-hour fuels; the result in controlling fire spread isn't great.

Fire won't "back off" by dropping scooping aircraft and helo buckets nearby. Nor do ground troops wait for a fire to "back off." Air assets are tools that ground troops request or use to apply to specific parts of a fire, in order to assist them in working the fire. Ground troops often work the fireline directly with shovels, pulaski's, handlines (hoses and water or foam), lighting backfires or backburns, running dozer or cat lines to cut away fuels and create fire breaks, and other tactical methods of fighting fires. In accomplishing this mission, they may request a helicopter to put water on a hotspot or to work a segment of a flank. They may look for a retardant drop to back up a bulldozer line or a road, to prevent spread across the road. In each case, the retardant use or water use is only one tool of many that the ground troops have at their disposal when working the fire.

Initial Attack planes are often the first one on scene, and in some cases, do end up working the entire fire from the air. These efforts are always considered a temporary measure, buying time for a helattack team or hotshots to come in and hit the tree with a chain saw, dig a line around it, or do whatever is necessary to actually control and put out the fire.

Often as not, the most effective means of putting out a fire is to supervise it burning itself out. Air assets are put in use to attempt to reduce damage to danger to structures of personnel until that happens. A lot of fires are far beyond the capability of man to control, or extinguish, and firefighting efforts, both in the air and on the ground, are futile motions that take place in earnest, until nature decides enough is enough.

Large air tankers are one tool in the toolbox...but only one. You need not only the aircraft, but enough bases capable of supporting them, close enough to fires, spread throughout the country, to do some good. The result was that the fire burned over our line before we could load and return with more retardant, and we were effectively wasting our time. The State of Florida wanted us to keep dropping however, because often as not it's as much a matter of public relations as it is doing anything effective. It was a given that we couldn't control the fire, but it was important that the public felt like every effort was being made to do so.

Fleet grounding:  In the United States, most of these aircraft are privately owned and contracted to government agencies, and the National Guard and the U.S. Marines also maintain fleets of firefighting aircraft. On May 10, 2004, The U.S. Forest Service (USFS) and the Bureau of Land Management (BLM) suddenly announced that they were cancelling contracts with operators of 33 heavy airtankers. They cited liability concerns and an inability to safely manage the fleet after the crashes of a C-130A Hercules in California and a PB4Y-2 in Colorado during the summer of 2002. Both aged aircraft broke up in flight due to catastrophic fatigue cracks at the wing roots, so sadly as a result of the new legislation no A-26's currently fly in an air tanker capacity.