Key takeaways
- An ATC is a simple tube-style belay device that creates friction via the rope bent over a carabiner.
- It's light, cheap, and versatile — handles single and double ropes for belaying and rappelling.
- It has NO braking assist; it relies entirely on the belayer's brake hand.
- Many have 'guide mode' to belay a follower from above on multi-pitch routes.
Black Diamond brand name: Air Traffic Controller.
What an ATC is
An ATC is a tube-style belay device — a simple metal tube you thread the rope through and clip to your harness. The rope bends sharply over a carabiner inside the device to create the friction needed to belay and rappel. ‘ATC’ (Air Traffic Controller) is a Black Diamond brand name used generically for tube devices.
How it works
You push a bight of rope through the device, clip it with a locking carabiner, and the sharp bend creates friction. Pulling the brake strand down to the locked-off position multiplies that friction to catch a fall or control a descent. Critically, the ATC has no mechanical braking assist — the brake hand must stay on the rope at all times.
On a multi-pitch route, a leader uses their ATC in ‘guide mode’ to belay the follower up from the anchor — the device auto-locks under load in that orientation — then threads both rope strands through it to rappel the descent.
ATC vs GriGri
The ATC is lighter, cheaper, and handles double-rope rappels, but relies fully on your brake hand; the GriGri adds assisted braking. Many climbers carry both. See GriGri vs ATC.
The bottom line
The ATC is the simple, versatile workhorse of belay devices: light, cheap, and capable of belaying and rappelling on single or double ropes. It has no braking assist, so it depends entirely on a constant brake hand and good technique. For assisted braking and easy hangs, climbers reach for a GriGri instead — but the ATC remains a staple, especially for multi-pitch and rappelling.
Frequently asked questions
What is an ATC?
An ATC is a tube-style belay device: a small metal tube you thread the rope through and clip to your harness, where the rope bends sharply over a carabiner to create the friction needed to belay or rappel. 'ATC' (Air Traffic Controller) is a Black Diamond brand name commonly used for tube devices in general.
How does an ATC work?
You push a bight of rope through the device and clip it with a locking carabiner. The sharp bend of the rope over the carabiner creates friction, and pulling the brake strand down to the locked-off position multiplies that friction to hold a fall or control a descent. The brake hand must stay on the rope at all times — the ATC has no mechanical assist.
ATC or GriGri?
An ATC is lighter, cheaper, simpler, and handles double ropes for rappelling, but relies entirely on your brake hand; a GriGri adds an assisted-braking cam that helps lock the rope and makes holding a hanging climber easier, but is heavier, pricier, and single-rope. Many climbers own both. See our GriGri vs ATC comparison.
Sources
- Belay devices & technique — American Alpine Club
- Belaying safety — UIAA