For me it is usually excess speed, or too much power used to slow down descent and not reduced properly.
In addition to the factors mentioned above, a higher than necessary approach speed also increases the sensitivity of the controls.
A lot of flying, including the amount of force/pull required to flare, depends on muscle memory. You know (and need to know) how much to pull to flare, because things happen too quickly for a visual feedback loop. But if your speed is higher than usual, the same pull on the yoke leads to a higher pitch up. A balloon in other words.
Where I fly gliders, there’s a bunch of trees close to the side of the approach path, just before the touchdown zone. When the wind is from that direction they cause a lot of turbulence. So we carry some extra speed through the turbulence, but once we’re in the clear air we need to start our hold-off immediately and bleed off the excess airspeed above the landing zone. The first few times this always leads to ballooning, until you become aware of what’s happening.
Thank you all for your input.
I too think it is excess speed. I rarely fly shallow approaches – the sort routinely seen in GA, with lots of power needed all the way down.
