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Since density altitude is perhaps the single most important factor affecting airplane performance, a review of the effects of density altitude is in order. An increase in air temperature and/or humidity significantly decreases power output and propeller efficiency. 

The engine produces power in proportion to the weight or density of the air. Therefore, as air density decreases (high density altitude), the power output of the engine decreases. Also, the propeller produces thrust in proportion to the mass of air being accelerated through the rotating blades. If the air is less dense, propeller efficiency is decreased. 

The problem of high density altitude operation is compounded by the fact that when the air is less dense, more engine power and increased propeller efficiency are needed to overcome the decreased lift efficiency of the tow plane’s wing. This additional power and propeller efficiency are not available under high density altitude conditions; consequently, tow plane performance decreases considerably. 

The winds aloft should be continuously evaluated to help determine the glider release area and always attempt to release the glider upwind of the airport. Code of Federal Regulations (CFR), part 91, section 91.309 (a)(5) states, “The pilot of the towing aircraft and the glider have agreed upon a general course of action, including takeoff and release signals, airspeeds, and emergency procedures for each pilot.” If there is any doubt that this rule has not been complied with through briefings or published and agreed upon standard operating procedures, ensure both you as the tow pilot and the glider pilot are absolutely clear on all aspects of the upcoming tow. 

## On the Airport 

The tow pilot must develop an awareness of the direction of the tow plane’s prop blast. Blasting launch personnel and glider canopies with all sorts of debris is undesirable and potentially dangerous. Whenever possible, turn away from any ground operations. Prior to taking the active runway 

for tow line hook-up and takeoff, if available, monitor and announce your intentions on the Common Traffic Advisory Frequency (CTAF). 

## Ground Signals 

In most cases, the Standard American Soaring Signals are used to communicate between the launch crew and tow plane. In some cases, however, specific local procedures may be in effect. The tow pilot should be thoroughly briefed on any specific local procedures. The tow pilot may be required to observe these signals through the mirror or through an additional signal relay person positioned safely on the side of the runway adjacent to the tow plane. The ground signals are listed below and are also presented as illustrations in Chapters 7 and 8 of this handbook. 

• Take up slack—the take up slack signal is given by the ground crewmember moving his or her lowered arm from side to side. When you receive this signal, slowly taxi the tow plane forward to take up the slack in the tow line. When all the slack has been taken from the tow line, expect to receive the “hold” signal from the ground crew. 

• Hold—this signal is given by holding the arms out straight. 

• Pilot ready, wings level—when the glider pilot is ready for takeoff, a thumbs up signal is given and the wing runner will level the wing to the takeoff position. 

• Begin takeoff—the glider pilot waggles the rudder with the wings level and the wing runner signals with a circular motion of the arm. When ready for takeoff, the tow pilot should broadcast on the CTAF that a glider launch is about to be initiated. For example, “Tallahasee traffic, N12345 taking off Runway 33, glider in tow, Tallahasee.” Remember, 14 CFR part 91, section 91.309, requires that before conducting towing operations within Class B, C, D, or E airspace designated for an airport, or before making each towing flight within such controlled airspace if 

