On Sunday, June 1, 2014 5:20:14 PM UTC-6, Kevin Christner wrote:
I had my first "rope break" ever today. I was approximately 200-250ft above the ground. Emergency procedures were not a problem.



The Tost released for some reason. Its a nose hook so the back release mechanism could not have been the culprit. Further testing with the wheel break on the ground revealed no problems so I took another tow and had no problems. The ring may not have been engaged properly (doubtful) or the slack I got in the rope was just too much when it tightened back up (probable but the release still should have held).



In any case has anyone else ever experienced an actual emergency unplanned release? In 14 years of flying I have never heard of one. Good thing we do practice this.



2C

I think it's worth inserting in this thread that the Germans suffer essentially zero aero tow PT3 accidents. The US could do the same by strictly observing FAR 91.309, FAR 91.9 and OSHA CFR 1915.112 on rope working strength where life is at risk as well as the Tost specifications on ring pair wear limits. The US and German regulations are essentially the same.

It works like this. Start by using a weak link at the glider as required by the glider flight manual (FAR 91.9) and a weak link 25% stronger at the tug (FAR 91.309) then use a rope 8x as strong as the strongest weak link (CFR 1915.112).

AFAIK, the strongest aero tow weak link called out in a glider manual is 2,436 Lbs-F (LAK-20) so CFR 1915.112 would require a rope with at least 19,500 Lb-F breaking strength. 3/8" Amsteel Blue from Sampson Rope would just meet this requirement. http://www.samsonrope.com/Pages/Prod...?ProductID=872

This rope would be much more expensive than what is commonly used now but it would last much longer - and the lives it would save would be priceless. Rope breaks would be a thing of the past.

A possible argument against Amsteel Blue is its very light weight so rope slack might float above the glider risking entanglement. This could be overcome by using a urethane rope coating as is used on helicopter slings to make the rope heavier and far more abrasion resistant. With a urethane coating, the rope should last decades.

I know someone will point out that a Schweizer hook is limited to 1,200 Lbs-F so it's impossible to comply with 91.9 and 91.309 using this hook. Yep, that's what it means. It IS possible to comply using the Tost tow plane hook.