Be 800ft, they hook a flag every 200ft on the cable so the ground observer knows what height you are at if your chute fails. He will shout to open your reserve over a megaphone. If the reserve doesn't open you take them back to stores to be replaced as one first time jumper was told by his PTI. It's very quiet up there in the gondola, just the sound of the wind in the rigging.
The Irish army SAS can't afford new chutes they are all WWII second hand ones, are told not to open them until they are ten feet from the ground in case they fail. One lad asked what happened if the chute fails? The reply was, "Jesus Christ man you can jump ten foot can't you".