Corking and the speed differential

When a vertical flyer loses control, they slow down fast, and everyone above them keeps falling at full speed. Most of the safety habits in freefly come back to that: where you break off, why you learn back-fly first, why you keep out of the column above another jumper, and why groups stay small until everyone is ready.

What corking is

A head-up flyer falls at somewhere around 220–260 km/h, and a head-down flyer is faster again. A belly flyer falls at roughly 190 km/h. Corking is a sudden, unplanned drop from a vertical position into a flatter, slower one: a sit that drops onto the back, or a head-down that loses its line and flattens out.

Australian safety columns were warning about corking as early as 2009: a freefly collision can kill, or can injure a jumper badly enough that they cannot deploy.

The speed difference is what makes it dangerous. USPA guidance puts a typical cork from vertical to belly at about 280 km/h down to 190 km/h. A flyer directly above closes that gap at around 90 km/h, with very little time to react.

How it shapes freefly

A hit at that closing speed carries far more energy than anything in belly flying. That is why the recovery position is trained as a reflex, and it explains several other habits:

• Back-fly comes first, because it is the recovery position for both head-up and head-down. You learn to get out of trouble safely before you learn to go fast.
• You learn to recover to back-fly reliably whenever you become unstable, before you fly relative to anyone. Closing on another person at vertical speed without that skill puts both of you at risk.
• On approach, you stay out of the column directly above or below another vertical flyer. Lanes are assigned so that when someone corks, nobody is overhead.
• Breakoff and deployment plans keep the sky clearing while speeds change at the end of the jump.

What it means for training

Corking is why progression here is measured by what you can fly, and jump numbers are only a guide. It is also why the recovery position is trained until it is a reflex. You rehearse it on the ground with your eyes open and closed, then, if you become unstable, recover to back-fly, in the recovery position, before you approach anyone again. More on the recovery position.

A stable back-fly with a wide speed range is a foundation for the same reason. The wider your recovery range, the more of the sky you can fall through safely when you become unstable.

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Advisory, educational content. Speeds and figures are typical guides and vary with body size, suit, altitude and position. Follow the rules of your federation and your drop zone.