•  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 12-6.  It is both the tow pilot and glider pilots responsibility  to check the condition of the tow rope before flight. •  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. Tow Rope Strength Requirements Tow Rope Inspection 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  possiblility that the Tost tow ring will become stuck in the  hitch mechanism making tow rope release impossible). 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:  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: 12-4 Schweizer ring Tost ring