Equipment Inspections and Operational Checks

Tow Hook

There are typically two types of tow hooks used in the United States: Tost or Schweizer. The tow hook must be inspected for proper operation daily and prior to any tow activity. [Figure 12-4]

Schweizer Tow Hook

Prior to use, the tow hook and release arm should be inspected for damage, cracks, deformation, and freedom of movement on the pivot bolt. Visually check the tow hook and ensure that the hook properly engages the release arm. Inspect the rubber spacer for general condition and check the condition of the release cable. Inside the cockpit, check to see that the manual release lever is not rubbing against the aircraft seat or any other obstructions, and check the security of the release handle assembly and the cable attachment.

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The following operation checks should be performed to the tow hook:

Attach the tow line to the tow hook and apply tension on the line in the direction of tow.
With tension on the tow line, have another person pull the release control in the tow plane cockpit and check for proper release of the tow line.
If the tow line does not properly release, restrict the tow plane from towing duties until repairs can be made.
Reattach the tow line and apply a moderate tug in the direction of tow.
Inspect the release assembly to ensure it has remained completely closed.
If the release assembly has opened, even partially, restrict the tow plane from towing duties and repair the tow assembly.

Tost Tow Hook

Before use, ensure that the release hook opens completely when the cockpit release is pulled to its fullest extent. The release hooks should touch the tow hook ring. If the release mechanism is not working correctly, it should not be repaired by anyone other than the Tost Factory. Inside the cockpit, check to see that the manual release lever is not rubbing against the aircraft seat or any other obstructions, and check the security of the release handle assembly and the cable attachment. When the cockpit manual release lever is released, the tow hook should return to the fully closed position. Before each use, check the tow hook and ensure that it is free of dirt and/or corrosion. It is important to confirm that the tow plane end of the tow rope is fitted with a Tost tow ring.

The following operation checks should be performed to the tow hook:

Attach the tow line to the tow hook and apply tension on the line in the direction of tow.
With tension on the tow line, have another person pull the release control in the tow plane cockpit and check for proper release of the tow line.
If the tow line does not properly release, restrict the tow plane from towing duties until repairs can be made.
Reattach the tow line and apply a moderate tug in the direction of tow.
Inspect the release assembly to ensure it has remained completely closed.
If the release assembly has opened, even partially, restrict the tow plane from towing duties and repair the tow assembly.

Tow Ring Inspection

Tow ring inspection should begin with checking for wear and tear. The rings should not be used if they have deep scratches or dents. Like the tow hitch assembly, there are two types of tow rings: Schweizer and Tost. [Figure 12-5] The Schweizer tow ring is two inches in diameter and made of high grade, one-quarter inch steel that has been magnafluxed with good weld. The Tost tow ring is also made of high grade steel and available through most glider supply companies.

Figure 12-5. Schweizer tow ring and a Tost tow ring.

Always ensure that the tow line is configured for the proper type of hitch being used. For example, a Schweizer tow ring will not fit into a Tost tow hitch, but a Tost tow ring can be placed on a Schweizer type tow hitch (with the great possibility that the Tost tow ring will become stuck in the hitch mechanism making tow rope release impossible).

Tow Rope Inspection

Although the pilot of the glider is primarily responsible for the selection and inspection of the proper tow line, it is also the duty of the tow pilot to confirm that the tow line selected meets the requirements of the Federal Aviation Administration (FAA) Regulations and is acceptable for use. [Figure 12-6] The tow line should be inspected as follows:

Check the entire length of the tow line for abrasions, security of splices, and general condition.
The tow line should be free from excess wear; all strands should be intact, and the line should be free from knots (knots in the tow line reduces its strength by up to 50 percent and causes a high spot in the rope that is more susceptible to wear).
Pay particular attention to the ring area to which the glider attaches because this is also a high-wear area.
Consideration should be given in replacing the tow rope after a period of time due to usage and ultraviolet (UV) exposure from being in the sun and exposed to the elements.
Ensure tow line strength is appropriate for the glider being towed.

Figure 12-6. It is both the tow pilot and glider pilots responsibility to check the condition of the tow rope before flight.

Tow Rope Strength Requirements

Stated in the 14 CFR part 91, section 91.309, the minimum tow rope strength is eighty percent of the gliders maximum certificated operating weight. The maximum strength is twice the maximum certificated operating weight. The maximum certificated operating weight can be found in the specific pilot’s operating handbook (POH) for the glider and may be the maximum certificated gross weight at takeoff. Figure 12-7 shows the strength of some ropes that are typically used. If the tow rope has a breaking strength more than twice the maximum certificated operating weight of the glider being towed, a safety link (weak link) has to be installed at the point of attachment of the glider and the tow plane with the following breaking strength requirements:

Safety link (weak link) at the glider end:
Minimum strength = eighty percent of the glider maximum certificated operating weight.
Maximum strength = twice the maximum certificated operating weight. [Figure 12-8]
Safety link (weak link) at the tow plane end:
Strength requirements = greater, but not more than twenty five percent greater than that of the safety link on the glider end, and not more than twice the maximum certificated operating weight of the glider.

Figure 12-8. Safety link strength requirements. [click image to enlarge]

Tow ropes and cables are made of many different reliable materials, such as nylon, step-index fiber from Red Polyester, Hollow Braid POLYPRO, Dacron, steel, and Polyethylene. [Figure 12-9]

Figure 12-9. Tow ropes and cables are made of many different reliable materials such as nylon, step-index fiber from Red Polyester, Hollow Braid POLYPRO, Dacron, steel, and Polyethylene.

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