Gate Flutter and Gate Shutter Explained

There are two types of scenarios that will unintentionally cause a carabiner’s gate to open, gate flutter and gate shutter. Understanding these situations can inform decisions when choosing which carabiners we use and where we use them. Below we explain the differences between these two distinct situations and what causes them.

Gate Flutter

Gate flutter is when the movement of the rope through a carabiner creates a harmonic vibration in the carabiner gate, causing it to repeatedly open and close slightly (“fluttering”). This could be caused by a really big fall where a lot of rope suddenly passes through and imparts weight on the carabiner.

Flutter is caused by a lot of friction from the rope zipping through a carabiner when a lot of weight is involved, similar to a bow on a violin string.

Gate flutter happens more dramatically on solid gate carabiners versus wire gate carabiners which is why many folks have recommended using wire gate carabiners on the rope-end of climbing protection like cams, alpine draws, and quickdraws.

Gate Shutter

Gate Shutter occurs when the gate opens and “shutters” due to the spine of the carabiner hitting against something hard (rock, other hardware, etc). This can happen when a loosely hanging carabiner is suddenly loaded over an edge, or anywhere that something juts out from the wall, causing the carabiner to slap against the rock.

It’s helpful to think of gate shutter happening from a sudden ‘smack’, usually when a carabiner goes from being floppy in the air to loaded suddenly against a surface.

You can see an example of gate shutter in action on this non-scientific YouTube Video:

Should I be worried about gate shutter or flutter?

The concern with both of these scenarios is that they create potential moments when a carabiner isn’t closed completely. Carabiners are tested and certified to have certain strength ratings and the certification for an open carabiner is significantly less than a closed one. So the worry some climbers have is that when flutter or shutter opens the carabiner gate at the same time the full force of the fall is absorbed, you are now in an “open gate” position, and the carabiner isn’t as ready/strong as it could be.

Although this logic is true, that the carabiner would be loaded in a weaker open gate position, it isn’t concerning for most climbers due to the high certification standards of a carabiner.

Currently, the UIAA and CEN certification for carabiners states that (depending on the shape) they must hold 5-7kN when open, which is equivalent to 1129 lbf of force. It isn’t likely that climbing falls can generate these forces (significant falls have been documented in the 3kN range) but it isn’t totally impossible, just extremely unlikely. (To our knowledge, this has never been recorded as the reason for an accident / carabiner breaking.)

What can I do if I’m worried about gate shutter or flutter?

The good news is there is one very easy thing you can do if you’re concerned about either of these scenarios: use a locking carabiner. This might sound silly to some, but if you consider that the majority of the friction on a sport climb happens at the first quickdraw and that many folks use stick clips to hang them anyway, simply pre-locking a draw on the rope is a pretty simple and low impact way to create some extra safety.

Note: We’re not saying use a locking carabiner for every quickdraw. It would be reasonable to use a locking draw for the first bolt (most dangerous fall potential) or when there is a poorly placed bolt (or trad placement) where the hanging carabiner could potentially face rock interference.

Additional ways to reduce occurrence of flutter

• Use stainless steel carabiners or carabiners with stainless inserts in the rope basket. Steel is much slicker than aluminum and will generate significantly less friction (and thereby less vibration) which will reduce if not erase the occurrence of gate flutter.
• Use wire gate carabiners. Carabiners with less gate mass will not be affected by harmonics so are less susceptible to vibration.

Additional ways to reduce occurrence of shutter

• Be mindful of the direction of load when you clip your rope to protection. For bolts and ice screws, choose a shorter or longer quickdraw that will allow a carabiner to avoid hitting protruding edges if you were to suddenly fall and load it.
• For trad gear placements, don’t over-extend alpine draws that might swing and slap against features.

Bottom Line

It’s cool to know why gate flutter and gate shutter happen, and to know what the potential weak points are with gear we trust our lives to. Though gate flutter and gate shutter are rarely on our minds due to the enormous safety margin built into carabiner certifications.

And, it is this large certified safety margin that is why we only buy carabiners from trusted climbing companies that we know are certifying their gear (and we avoid new Amazon brands that we cannot check their certification via the UIAA website).