S-2T: making the retardant drop

When an air tanker such as an S-2T is deployed to a wildland fire, the air tanker pilot will be in touch with either the incident commander on the ground or some one known as the air tactical group supervisor (ATGS). The ATGS oversees aerial support for the fire, including retardant drops from a tactical aircraft, sometimes known as an air attack plane flying over the fire. The ATGS will be in touch with the incident commander (IC) on the ground. CAL FIRE’s tactical aircraft are known as OV-10’s and there is one OV-10 at each air attack base. The ATGS, after consulting with the IC, will give the S-2T tanker the information that s/he needs to make the drop, including but not limited to the location. In initial attack the S-2T pilot may make his own determination about the necessary settings and where to make the drop.

The settings that S-2T air tanker pilot (and other air tanker pilot’s) use for the retardant drops are on a panel on the cockpit. This is the same one pictured in the preceding post, so I will be using that picture as a reference. Perhaps you will want to open up a new window in your browser so you can look at TL Stein’s photograph and follow along.

The pilot adjusts the dial on the left to set the amount of retardant to be dropped while the dial on the right is set to determine the coverage level (also known as gpc). The coverage level is gallons of retardant per 100 square feet. Coverage levels are somewhat technical, depending on the type of vegetation on fire (fuels) and the fire behavior. The coverage settings dial is scaled from .5 to a maximum of 8 (gallons per 100 square feet). A switch known as the arm-disarm switch is set in the disarm position until it is near time to make the actual retardant drop. This prevents accidental drops. The button that the pilot pushes to make the drop, drop control switch (not pictured), is on the pilot’s control panel for ease of access. The door control (switch in the middle), is set to automatic.

Once the settings on the two dials are made, and the pilot is at or near the location and correct altitude for the drop -- 150 feet above ground level for the S2-T -- the pilot flips the arm-disarm switch to arm the system. The pilot has only to push the drop control switch at the appropriate time, the tank doors open and the drop is made. It is not merely the cockpit controls that make the retardant drop possible, there are various avionics (aviation electronics) and hydraulics that make the retardant drop possible.

If there is an emergency situation, the pilot can make an emergency retardant drop by pulling an emergency handle (not pictured).