Two audibles: altitude awareness at freefly speeds

Freefly speeds change the altitude problem in two ways. There is less time than a belly jumper is used to, and the device most flyers lean on can fail without making a sound. That combination is why altitude awareness in freefly is built around redundancy rather than a single alarm.

Time compresses

Vertical fall rates are high. Head-up work runs around 220 to 260 kilometres per hour, and head-down runs from about 270 to well past 400, per the APF Freefly and Angles Guide (APF006). The figures come from different sources and are not clean unit-for-unit equivalents, but the direction is clear: the ground arrives sooner.

Working time shrinks with it. A freefly descent from around 13,000 feet can be roughly 20 seconds shorter than the same belly jump, and head-down working time can be around 40 to 46 seconds against roughly 60 on the belly. The practical discipline is to check altitude often, at least every five seconds and after every manoeuvre, so the clock never gets ahead of the flyer.

Why two audibles

An audible altimeter is a safety-critical device that can fail silently. It can go flat, mis-set, or simply not sound, and nothing about that failure announces itself in freefall. In a group there is a natural backstop: a flyer who misses their own alarm can see others break off and follow. A soloist has no such backstop, which is why two functioning audibles are treated as best practice before any solo freefly.

Fence that argument carefully. The group backstop explains why solo removes a safety net. It is never a reason to offload altitude awareness onto other people. Relying on “someone will break off and I will follow” is a diffusion-of-responsibility hazard where nobody is actually the reference. Every flyer runs and checks their own audibles to the full standard.

Where practical, use two different models, or at least devices with different battery ages and states, so a single common cause such as a shared firmware quirk or a cold-soaked battery is less likely to silence both at once. Two alarms do nothing, though, for a tone the flyer cannot identify. Know each alarm’s sound cold, and confirm against a visual altimeter before any unplanned deployment.

The Australian Skydiver Magazine (ASM 111) records a case where a flyer believed a low hard-deck alarm had sounded at around 8,000 feet, flipped and deployed immediately, and put another jumper close above into an evasive move.

Setting audibles for the jump

On angle jumps the audible is the group’s shared clock, set to the briefed breakoff. On staged big-way breakoffs the setting is personal: each flyer sets their audibles to their own wave’s altitudes, and a mis-set audible quietly defeats the whole staged plan.

A head-down two-stage plan might, for example, break stingers at 6,500 feet to deploy at 5,000, and the base at 5,500 to deploy at 4,000, with 1,500 feet banked per wave. The audible only helps if it matches the wave the flyer is actually in.

The equipment stack

The recommended stack is a visual altimeter, a functioning audible with a second one for solo and best practice, and an AAD. In Australia a functioning audible altimeter is mandatory on every freefly descent under the APF Operational Regulations. Progressive altitude assurance through freefall, such as a colour-cue visual altimeter, adds another layer.

And because deployment at freefly speed drives hard openings and diving line twists, which made up a large share of malfunctions in one 2022 quarter per the Australian Skydiver Magazine (ASM 109), wash off speed and get symmetrical before pitching.

The takeaway

Two audibles, two known tones, and a visual confirmation turn a silent single-point failure into a survivable one. The redundancy is for your own awareness, not a licence to borrow anyone else’s.

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Advisory, educational content. All altitudes are guides. Comply with your federation’s rules and your drop zone’s policies, and treat altitude awareness as your own responsibility.