How high can a helicopter fly before the air is too thin for its rotors to keep it in the air?

• THERE are three answers to this. The maximum altitude which can be reached during forward flight typically depends more on the ability of the engine to breathe the thinner air than the rotor's ability to provide lift. Turbine-engined helicopters can reach around 25,000 feet. But the maximum height at which a helicopter can hover is much lower - a high performance helicopter like the Agusta A109E can hover at 10,400 feet. However, if the helicopter remains in 'ground effect' - ie, if it is hovering close to high ground - its maximum hover altitude will be higher. The Agusta can hover in ground effect - 'HIGE' in helicopter jargon - at 13,800 feet. This is useful for mountain rescue missions.

  Russ Swan, Lambley, Notts. (rswan@innotts.co.uk)

• I think helicopters can fly up to 25,000 feet altogether.But many others think that scince there are tons of different helicopters that the type of the engine chooses how high it can go.

  Jenna Schaeffer, Sunburyl, Pennsylvania

• Black Bears are indigenous to North America and some parts of Australia. While Black Bears can reach a weight of up to 600 lbs, the Polar Bear is actually a larger animal in both weight and size.

  Aaron, Layton, Utah United States