Thoughts about breaking the carabiner

July 24, 2020

A white paper by Thomas Finsterwalder on the subject of aviation carabiners shows ways in which their durability can be tested and assessed in a standardized manner. Alu, steel and ego breaks, only my carabiner doesn't? // Source: Finsterwalder I recently reported on the subject of carabiner break on Lu-Glidz and recommended not to fly carabiners until the end of the day, but to replace them regularly after a certain period of use, to be on the safe side (see Exchange before it breaks). Thomas Finsterwalder from Finsterwalder-Charly has thought about this problem and has written a white paper (online and available as a PDF). In it, he not only describes the technical background again. Rather, it also formulates requirements for a uniform test procedure with which all aviation carabiners on the market can be tested and compared with regard to their long-term strength (so far there is no uniform test standard for aviation carabiners). The bottom line is to simplify the question: Can you trust a certain carabiner model to survive a certain time (e.g. five years) of regular flight operations intact? Steel is not always the better choice In the white paper, Finsterwalder names some factors that play a role in the fatigue strength of carabiners. And it shows how complex the interplay of these factors can be. For example, lighter aluminum carabiners can be more flexible, so they tend to bend under load in such a way that the catch snaps into force. The result is less vibrations with load changes, i.e. less material fatigue and longer durability. Also interesting is the question of how big the support straps are at the top of the carabiner. The wider it is, the sooner the straps can slide forward and then transmit higher forces or larger vibrations into the material via a stronger leverage effect, which reduces durability over time. Narrow carabiners or those that cause the straps to slide backwards have an advantage here. Even steel carabiners do not have to perform better per se than aluminum models because of the firmer material. Since they are significantly stiffer, they can only be trapped at higher loads, before the vibrations add up. In the white paper, Finsterwalder shows that a certain steel carabiner after its test procedure in mono operation (with the load of only one pilot) would not have a calculated "fatigue life" of five years. Ie an earlier exchange would also be recommended here. However, the term fatigue strength of carabiners per se is vague and only an auxiliary variable. Carabiners can be installed in a harness for five years, but during this time you can fly a lot or a little, with high or low loads, with a lot or little dynamics, in calm or very turbulent air. All of this affects how hard the carabiner material gets tired and the risk of breakage increases over time. Unfortunately, you cannot see carabiners from the outside, whether they have just cushioned thousands or tens of thousands of load changes. In principle, it would definitely be welcomed if a standardized test procedure for aviation carabiners were established - in the sense of better transparency and comparability for the pilots.

This article has been translated for your convenience and was originally written in alemão.