Is there a standard maximum altitude which skydiving planes can fly?
I am mainly asking about the sports activity, not military parachuting.
Qualifier: I am a master parachute rigger and taught sport skydiving for 10 years.
Standard jump altitude is 12,000 feet AGL - this is one turn of the standard parachutist's altimeter. This height provides 1 minute of freefall, is within reach of a Cessna with a decent engine and does not require supplementary oxygen. For most places, this means an operating altitude between 12,000 and 15,000 feet MSL.
Dropzones in high areas like Denver will reduce their jump altitude to 9,500 feet AGL mainly because the piston-powered planes take too long to climb higher and/or the upper part of the climb runs into the oxygen zone.
As paul mentioned, "standard" altitudes for sport skydiving facilities near sea level are in the 10,500-13,500 AGL range. Dropzones significantly above sea level typically either reduce their jump height to stay under 15,000 MSL or provide supplemental oxygen in the plane and go up to 18,000 MSL.
Many dropzones will offer jumps from 18,000 MSL for an additional fee over the regular jump. Supplemental oxygen is provided. Jumps in the 18,000-23,000 MSL range are also possible but rarer because of the increased needed for coordination with ATC. Above 18,000, the risk of hypoxia increases rapidly. This video shows jumpers suffering from severe hypoxia at 21,000'.
There is at least one facility in the United States that takes recreational skydivers up to 30,000 MSL. It requires additional training and wearing oxygen in freefall. This facility uses a King Air, and I know it has also been done from a PAC750.
If there's such a thing as a standard maximum altitude for sport parachuting, the best answer would be 15,000' MSL, as above this CFR 91.211 requires supplemental oxygen for all passengers - and providing this to sport jumpers would be an expensive nuisance.
Note that this does not vary with ground elevation - so indeed jumpers in the Denver area will not be able to get as high above the drop zone (and thus as much freefall time) as those starting from a lower altitude.
Note also that this is a limitation on people - there is no standard maximum for jump aircraft Some aircraft types (e.g. Cessna 182) would struggle to get anywhere near 15,000' MSL in a reasonable time. Others (e.g. Cessna Caravan) can haul a full load of jumpers to 15,000' MSL rapidly and without breaking a sweat. The Caravan could carry jumpers to its service ceiling of 25,000' provided they had oxygen and the pilot obtained ATC clearance (required above FL 180 = 18,000').
Paul said "Standard jump altitude is 12,000 feet AGL -This height provides 1 minute of freefall, "
that is incorrect actually...
Basic skydive has an exit altitude of 10,000 feet. This is the average altitude for skydiving here in the US and common to most Cessna aircraft dropzones.
This means you will skydive from 10,000 feet above ground level. At this height, your skydive will last 30 seconds - that's how long you'll be in freefall. You'll then have a few minutes under parachute as you make your way to the ground.
EXTREME SKYDIVING ALTITUDE: 14,000 FEET When you jump from 14,000 above ground level, you'll be in freefall for around 60 seconds.
THE HIGHEST DAILY JUMP is: 18,000 FEET
At a skydiving altitude of 18,000 feet, skydiving lasts for 2 minutes
Any way the correct answer is
basic skydive from 10,000 feet above ground level. At this height, your skydive will last 30 seconds