Appendix C C-1 APPENDIX C. POSSIBILITY OF D-RING REVERSAL OR DYNAMIC ROLLOUT
DURING WINCHING OR LONG LINE OPERATIONS C.1 Background.
1. Unintended disconnection between the helicopter winch hook and the primary engaging ring on the occupant’s rescue harness typically occurs during a pause in the winching sequence, when the ring in the rescue strop and the hook are temporarily relieved of the load. With no weight on the hook and ring, under the dynamic conditions of this type of operation, it becomes easy for the ring to travel up and flip over the tip of the hook and to rest on the spring-loaded keeper. The ring is now only supported by the spring-loaded keeper (see Figure C-1, Example of D-Ring Reversal).
Figure C-1. Example of D-Ring Reversal
2.
When the winching sequence commences, the load is reapplied, and the ring opens the spring-loaded safety catch and slips off the hook and the occupant or load falls to the ground.
3. HEC rescue winch hooks with exposed hook tips, such as the MS 18027-2A, do not prevent D-ring reversal or deflect the primary engaging ring safely back into the throat of the hook (see Figure C-2, MS 18027-2A Hook).
4. HEC rescue winch hooks with manually locking keepers or guards have a hand-operated mechanical latch or keeper lock, in addition to spring pressure used to initially close the keeper. Such designs are intended to prevent partial
Appendix C C-2 hook engagement and deflect the primary engaging ring safely back into the throat of the hook, thus preventing D-ring reversal (see Figures C-3, Hook with a Mechanical Lock Latch Gate Design, and C-4, Hook with a Simple Spring-Loaded Safety Latch or Keeper).
Figure C-2. MS 18027-2A Hook
Fi gure C-3. Hook with a Mechanical Lock Latch Gate Design
Appendix C C-3 Figure C-4. Hook with a Simple Spring-Loaded Safety Latch or Keeper
C.2 R ecommend Action.
1. Develop procedures which list the specific D-rings or equipment which may be attached to a specific rescue hook wherein the possibility of D-ring reversal is physically impossible.
2. Use only rescue hooks which have a mechanical locking keeper or guards to prevent ring reversal or dynamic rollout.
3. Ensure winch operational training is tailored for each helicopter type and winch combination and is completed on a regular basis.
4. Operate and maintain winches, hooks, and harnesses in accordance with approved data.
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