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Retardant Drop Test of the Hatfield Gate on an AT-502B Air Tractor

A photo of a plane dropping retardant.

With the advent of turbine power and 500- to 800-gallon (1,900- to 3,030-liter) retardant tanks on larger single-engine agricultural aircraft, State and Federal agencies are taking a new look at these aircraft. Their maneuverability allows them to place retardant precisely in difficult terrain. Single-engine airtankers can also operate from unimproved short airstrips closer to a fire, shortening their turnaround time.

Recently, Wildland Fire Chemical Systems personnel at the MTDC conducted a series of drop tests on a Hatfield Gate made by Turbine Conversions. The gate was installed on a single-engine AT-502B Air Tractor. The objectives of the tests were to measure flow rates and negative internal pressures at different door openings, to check door opening variations and split-load capabilities, and to estimate the ground pattern coverage of the retardant at different airspeeds. Both inflight and static (on the tarmac) drops were made during this test.

Drop guides are also available on the Internet at:

Printed copies of the drop guides for other aircraft are available from Jody Faircloth, MTDC publications (phone: 4063293978, fax: 4063293719, e-mail:

For more information on the drop guides and testing, contact Greg Lovellette, project leader (phone: 4063294815, fax: 4063293719, e-mail

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