On Thursday, May 14, 2020 at 3:35:18 PM UTC-4, Duster wrote:
Has anyone heard of or experienced a case where the pull of the glider's release handle during flight failed to result in the rope dropping off the release mechanism? Last summer two of us were under tow when turbulence threw us too high above the tug (or sink drove the tug too low) @~2,000ft agl. One of us remarked that "We need to release", and we each pulled the handles. I pulled mine again at least twice and I distinctly remember the cable moving a few cm each time. We turned away from the tug, but after a few seconds I thought I heard a loud bang accompanied by a slight, transient vibration, but no nose movement. Pulled the handle several more times. First I'm thinking we hit the towplane, but then I saw him below and ahead of us with about 4-6' of rope trailing off his Tost release, then radioed him to report the rope break. An inspection did not reveal any evidence that the rope had gotten hung up on the gear doors, wing or empennage. Testing the release gave the normal rope drop after a few mm's of pull, even under heavy tension. The other pilot didn't hear the "break", but the flight logger did record it as a spike of noise on the trace. Any hypotheses on this one?

Perhaps in a related incident, the 2017 Pawnee fatality accident report where there was intra-cockpit video, the glider pilot reported that (after an admitted distraction) he got high on tow, noticed some rope slack, pulled the dive brakes and released the rope. The GoPro showed almost full deployment of the spoilers, first a short movement of the release cable, followed by a "snapping sound", followed by a longer slack in the cable. The report also revealed a short length of rope hanging from the Pawnee (with a high tension break). The NTSB could only conclude that the tug pilot had, for some unknown reason, lost control. Other factors were suggested. The similarity between that incident and ours was that each glider pilot pulled the release handle, assumed the rope fell away but ended up with a rope break. That's my reading of the report, but I may have missed something.

Our Club had a similar sounding event a couple of years ago. Our Pawnee has the TOST reel system. The glider was a ASK 21. The glider pilot was a long retired airline pilot, recently returned to flying. he was solo in the '21, got distracted, and way out of position. He pulled the release, but no release. He did not recall (or maybe know) the Pawnee had the ability to cut the rope. He decided he had to break the rope and tried. He couldn't. The Tug pilot, a multi-thousand hour duster veteran, was about to dump him, when the rope broke. Fortunately, there was enough height and they both recovered. The release was later checked on the ground and found to be OK. Replaced anyway.
Review of ethics's TOST installation manual and other information disclosed that the TOST release force required for an out of position release may be as high as 45 lb at the handle or knob. That is a much higher force than usual.

Hartley Falbaum