Introduction
Glider pilots in the United States commonly launch using an aerotow. [ Figure 12-1] An aerotow takes time but can
offer flexibility regarding energy, location, and altitude. Chapter 7: Launch, Flight Maneuvers, Landings, and Recovery
Procedures presents information from the glider pilot’s perspective. This chapter provides much of the same information
but from the perspective of the tow pilot.
Figure 12-1. Gliders commonly use tow planes to launch and obtain altitude.
While all pilots follow Title 14 of the Code of Federal Regulations (14 CFR) part 61, Certification: Pilots, Flight Instructors,
and Ground Instructors, and 14 CFR Part 91, General Operating and Flight Rules, the following sections sample some of
the requirements of interest to tow pilots:
• 14 CFR part 61, section 61.23—Medical certificates: Requirement and duration.
• 14 CFR part 61, section 61.69—Gliders and Unpowered Ultralight Vehicle Towing: Experience and Training
Requirements.
• 14 CFR part 91, section 91.15—Dropping Objects
• 14 CFR part 91, section 91.309—Towing: Gliders and Unpowered Ultralight Vehicles
Equipment Inspections & Operational Checks
Tow Hook
Tow plane equipment in the United States typically uses one of two types of tow hooks: Tost or Schweizer. [Figure 12-2]
The tow pilot should inspect the tow hook for proper operation daily and prior to any tow activity.
Chapter 12: Aerotow
Ring
Hook
Tow ring
To release
handle
Tow hook pulled up
To glider
Figure 12-2. Schweizer tow hook (left) and a Tost tow hook (right).
Schweizer Tow Hook
Prior to use, the tow pilot should visually inspect the tow hook and release arm for damage, cracks, deformation, and
freedom of movement on the pivot bolt. The inspection should ensure that the hook properly engages the release arm. The
pilot should also inspect the rubber spacer for general condition and check the condition of the release cable. Inside the
airplane, the pilot should verify that the manual release lever does not rub against the aircraft seat or any other obstructions
and check the security of the release handle assembly and the cable attachment. The pilot should also perform a functional
inspection. If the visual or functional inspection reveals an issue, the pilot should restrict the tow plane from towing duties
and repair the tow assembly.
The following functional checks should be performed:
• Attach the tow line to the tow hook and apply tension back on the line.
• With tension on the tow line, have another person pull the release control in the tow plane and check for proper
release of the tow line.
• Reattach the tow line and apply a moderate rearward tug.
• Inspect the release assembly to ensure it remains completely closed.
Tost Tow Hook
Before use, the tow pilot should ensure that the release hook opens completely when a helper pulls the release to its fullest
extent from inside the airplane. The release hooks should touch the tow hook ring. Inside the airplane, the pilot should
check to see that the manual release lever does not rub against the aircraft seat or any other obstructions. The pilot should
check the security of the release handle assembly and the cable attachment. When not pulling the manual release lever, the
tow hook should return to the fully closed position. The pilot should check the hook for dirt or corrosion and confirm that
the airplane end of the tow rope has a Tost ring. If the release mechanism does not work correctly, factory repair should
occur before any tow.
The following functional checks should be performed:
• Attach the tow line to the tow hook and apply tension back on the line.
• With tension on the tow line, have another person pull the release control in the tow plane and check for proper
release of the tow line.
• Reattach the tow line and apply a moderate rearward tug.
• Inspect the release assembly to ensure it remains completely closed.
Tow Ring Inspection
Tow ring inspection begins with a check for wear and tear. Tow pilots should take rings out of service if they have
scratches or dents. The tow ring design corresponds to the type of tow hitch assembly: Schweizer or Tost. [ Figure 12-3]
The Schweizer tow ring uses a single two-inch diameter high-grade, one-quarter inch steel ring magnafluxed with good
weld. The Tost tow ring consists of a pair of interconnected rings made from high-grade steel.
Schweizer ring
Tost ring
Figure 12-3. Schweizer tow ring and a Tost tow ring.
The tow pilot should only attach a compatible tow line ring to the tow hitch. While a Schweizer tow ring will not fit into
a Tost tow hitch, the tow pilot could mistakenly attach a Tost tow ring to a Schweizer tow hitch. If that happens, the Tost
ring might not release when the tow pilot actuates the release mechanism.
Tow Rope Inspection
Although the pilot of the glider has primary responsibility for the selection and inspection of the proper tow line, the tow
pilot should confirm the tow line and any required weak links meet the strength requirements of the Federal Aviation
Administration (FAA) Regulations and are acceptable for use. See chapter 6, Preflight and Ground Operations, regarding
tow line selection and inspection. Pilots should consider replacing the tow rope after a specific period of usage and
exposure to the sun or to the elements.
Density altitude affects airplane performance. An increase in air temperature or humidity, or decrease in atmospheric
pressure significantly decreases power output and propeller efficiency.
Abort Briefing
Using the computed takeoff data or actual takeoff point for the given conditions, the tow pilot should choose a physical
abort point on the runway [Figure 12-4] and brief the glider pilot on the abort point and abort procedures. If the tow plane is
not off the ground by the chosen abort point, the glider should release, or be released, allowing the tow plane to accomplish
a normal takeoff.
Abort point
Figure 12-4. A physical abort point on the runway should be determined and briefed to the glider pilot before starting the towing
procedures.
14 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 any doubt
exits about compliance with this rule through briefings or published and agreed upon standard operating procedures, the
tow pilot and glider pilot should make certain to clarify all aspects of the upcoming tow.
On the Airport
The tow pilot should maintain an awareness of the direction of the tow plane’s prop blast. Blasting launch personnel and
glider canopies with wind and debris creates an annoyance and danger. Whenever possible, the tow pilot should angle prop
blast away from any ground operations. Prior to taking the active runway for tow line hook-up and takeoff, if applicable,
the tow pilot can monitor and announce intentions on the Common Traffic Advisory Frequency (CTAF).
Ground Signals
In most cases, tow pilots use the Standard American Soaring Signals to communicate between the launch crew and tow
plane. In some cases, however, specific local procedures take precedence. The tow pilot should receive a briefing on any
specific local signals or procedures. The tow pilot might need 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. Chapter 7 of this
handbook, Launch, Flight Maneuvers, Landing, and Recovery Procedures has figures for the ground signals.
Takeoff & Climb
When ready for takeoff and if applicable, the tow pilot should broadcast the commencement of a glider launch. For
example, “Tallahasee traffic, N12345 taking off Runway 33, glider in tow, Tallahasee.” 14 CFR part 91, section 91.309(a)
(4) states, “Before conducting any towing operation within the lateral boundaries of the surface areas of Class B, Class C,
Class D, or Class E airspace designated for an airport, or before making each towing flight within such controlled airspace
if required by ATC, the pilot in command notifies the control tower. If a control tower does not exist or is not in operation,
the pilot in command must notify the FAA flight service station serving that controlled airspace before conducting any
towing operations in that airspace;”
When ready for takeoff and if applicable, the tow pilot should broadcast the commencement of a glider launch. For
example, “Tallahasee traffic, N12345 taking off Runway 33, glider in tow, Tallahasee.” 14 CFR part 91, section 91.309(a)
(4) states, “Before conducting any towing operation within the lateral boundaries of the surface areas of Class B, Class C,
Class D, or Class E airspace designated for an airport, or before making each towing flight within such controlled airspace
if required by ATC, the pilot in command notifies the control tower. If a control tower does not exist or is not in operation,
the pilot in command must notify the FAA flight service station serving that controlled airspace before conducting any
towing operations in that airspace;”
On takeoff, the tow pilot advances the throttle smoothly and quickly in one motion. [Figure 12-5] If the tow plane accelerates
and then slows down, the glider could overrun the tow line and snag the line in the landing gear. The glider pilot might not
have release capability if that occurs.
Figure 12-5. The tow pilot advances the throttle smoothly and quickly in one motion so that the glider does not overrun the tow line.
The tow pilot accelerates to liftoff speed keeping in mind that what will occur during the transition out of ground effect.
The tow plane leaving ground effect will:
• Require an increase in the angle of attack (AOA) to maintain the same lift coefficient,
• Experience an increase in induced drag and thrust required,
• Experience a decrease in stability and a nose-up change in moment, and
• Experience a reduction in static source pressure and increase in indicated airspeed.
These general effects point out the hazards associated with attempting takeoff prior to achieving the recommended lift-off
speed. Due to the reduced drag in ground effect, the tow plane may seem capable of takeoff well below the recommended
speed; however, lifting out of ground effect with a lower-than-normal lift off speed may result in poor initial climb
performance.
The glider will normally lift off first. The tow pilot should expect the glider pilot to correct for crosswind until the tow
plane becomes airborne. At this point, the tow pilot should remain alert to a glider climbing too high and lifting the tow
plane tail. Should this happen, the application of full-up elevator on the tow plane may not be sufficient to prevent an
accident, and the tow pilot should pull the release handle, release the glider, and regain control. As a rule of thumb, a glider
climbing 20 feet or more above a tow plane when using a 200-foot rope presents the danger of an upset.
After liftoff, the tow pilot should pitch up to establish a constant airspeed climb and expect the glider pilot to establish a
position directly behind the tow plane. Upon reaching a safe altitude, the tow pilot can initiate a turn to maintain the desired
departure path using bank angles limited to 15°–20°.
The tow pilot climbs at full throttle unless otherwise required by the POH. The fuel/air mixture should be leaned in
accordance with the POH for maximum power. Each specific model of glider has a published maximum aerotow speed, and
the tow pilot should know this speed, which may be very close to the minimum safe speed of the tow plane. [Figure 12-6]
Blanik L-23
Blanik L-13
SGS 2-33
SGS 1-26
ASK 21
93 mph
87 mph
98 mph
95 mph
108 mph
81 knots
76 knots
85 knots
83 knots
94 knots
Maximum Aero Tow Speed MPH Knots
Figure 12-6. Sample glider maximum aerotow speeds.
The towing speed results from consideration of several variables. The tow pilot determines the minimum towing speed
after considering minimum speed for proper engine cooling and stall speed of the tow plane, flies at a speed slower than
the maximum glider aerotow speed, and conducts the aerotow at the slowest safe speed sufficient for the glider to remain
under control. When towing a model of glider for the first time, the tow pilot should obtain a briefing from the glider pilot
to ensure compliance with minimum, maximum, and optimal towing speeds. An experienced tow pilot can determine if the
speed is sufficient for the glider by observing the glider wing profile in the tow plane mirrors. A tow pilot viewing a larger
than normal portion of the underside of the glider wing for a given tow position may indicate a high glider angle of attack
and the need for a slight increase in towing speed.
Because of the potential for low altitude emergencies, the initial climb should remain within gliding distance of the airport.
The tow should not climb in a direction that would prevent the glider from returning to the traffic pattern with the existing
headwind component. If the tow pilot allows the departure path to drift with a crosswind, it reduces the radius of a turn
back to the runway in the event of a low altitude emergency.
A thoughtful glider pilot communicates the intention to perform any maneuvers behind the tow plane. However, the tow
pilot should remain alert for any unannounced maneuvering. Glider pilots often practice maneuvers such as “Boxing
the Wake,” explained and illustrated in Chapter 7 of this handbook, Launch, Flight Maneuvers, Landing, and Recovery
Procedures. Once detecting this maneuver, which normally begins with the glider descending vertically from high tow
position to low tow position, the tow pilot should maintain a constant heading and a wings level attitude. After the “Boxing
the Wake” maneuver ends and the glider returns to a stabilized high-tow position, the tow pilot can maneuver as needed.
During tow, a glider instructor may demonstrate and teach slack rope recovery procedures. This maneuver normally
involves a climb to one side of the tow plane followed by a small dive to create slack in the tow line. The instructor will
then ask the student to take the controls and remove the slack out of the tow line without breaking the rope. The tow pilot
should not confuse this maneuver with a release. Chapter 8 of this handbook, Abnormal and Emergency Procedures,
contains more information regarding slack line procedures.
Tow Positions, Turns, & Release
Glider Tow Positions
Glider tow operations normally use the high tow position. However, the glider pilot could use a low-tow position in some
instances such as a cross-country tow. Either position places the glider outside the wake of the tow plane. [Figure 12-7]
High tow position
Wake
Low tow position
Wake
Figure 12-7. Aerotow climb-out.
Turns on Tow
The tow pilot can initiate turns upon reaching a safe altitude. The pilot should consider clearance, terrain, and wind
gradient. Turbulence and differential wing speed of the glider during turns are potential hazards. Tow pilots should make
all turns gently and gradually. The tow pilot expects the glider pilot will attempt to match the flightpath of the tow plane.
Due to the length of the wingspan, the glider typically rolls more slowly than the tow plane. Since the bank angles of the
tow plane and glider must match to fly the same path, the tow pilot normally uses a maximum of 15–20° of bank.
Approaching a Thermal
When approaching a thermal and planning a release, both pilots should look for other gliders and expect inbound gliders
from different directions. Since the first glider in the thermal establishes the direction of turn, any glider joining the thermal
should circle in the same direction as the first glider, and the tow pilot should position the flight in a manner that allows
the glider proper and safe entry to the thermal. The presence of several gliders in a thermal presents significant risk and the
tow pilot should remain clear of any crowded thermal activity.
Release
The winds aloft should be continuously evaluated to help determine the glider release area, and the tow pilot should always
attempt to release the glider within gliding distance of the airport considering the winds. The tow pilot should discuss the
planned release point with the glider pilot. Use of a consistent tow pattern allows the glider pilot to plan a release point.
Standard glider release procedures include [Figure 12-8]:
1. Some tension on the tow line prior to release allows the tow pilot to feel the release of the glider. A tow pilot looking
in the mirror may see a wrinkle in the tow rope after the glider releases.
2. The tow pilot expects the glider to turn right after release but should remain alert for non-standard maneuvering by
the glider.