By varying the hot air temperature, altitude can be maintained without having to release helium or to drop ballast.

Thus, the balloon need not drop solid ballast in the form of shot bags or water.

The balloon is what is called a super-pressure type, designed to stay at a constant altitude without the need to drop ballast regularly.

For a few days, the balloon can maintain altitude by dropping ballast when it vents.

He could slow its fall if necessary by dropping ballast, rather than by lighting up the fire.

"We were dropping ballast to try to keep in the air - that's what people saw falling," he said.

We've got to drop ballast or touch down.

To halt the descent a pilot most drop ballast, and when the ballast is exhausted the flight must end.

We can't maintain this at night and we'll need the burners or we'll be dropping too much ballast.

Everyone so far had dropped ballast to rise and dodge the enemy's blows.