How do you land a plane on water?

The ditching of an airliner into the Hudson River in New York, in which all 155 passengers and crew escaped alive, has been hailed as a textbook example of landing on water.

The plane, an Airbus A320, appears to have have hit a flock of birds shortly after taking off from the city's LaGuardia airport, before making an emergency landing in the river.

Captain Chesley Sullenberger III has been praised for his "masterful" landing, but how does a pilot safely attempt such a manoeuvre?

Although the likelihood of a waterborne landing is remote, all commercial pilots must undergo training for such an eventuality before qualifying. They are taught to follow a procedure - which, in its initial stages is similar to an emergency landing on solid ground. However, there may not be time in an emergency to follow it rigorously.

Having made a mayday call and alerted the cabin crew, those in the cockpit must ensure the undercarriage - the wheels - is retracted to aid a smoother landing and prevent warning sirens sounding as the plane nears the ground. The air conditioning would also be turned off to allow cabin pressure to match that outside.

There is an overriding need to slow down the craft. If there is still power to the engines and a wind of more than 25 knots, a pilot would be expected to fly into the wind to assist slowing. Wing flaps would also be fully extended. If there is time a pilot would be expected to burn as much fuel as possible, reducing the weight of the plane and so increasing buoyancy when it hits the water. On this occasion, however, the engines appear to have already cut out.

NY mayor hails 'hero' crash pilot.

As the aircraft nears the water, the pilot must try to continue slowing while, crucially, ensuring the aircraft does not "stall". In aviation the word has a different meaning to that in motoring, for example. Stall is an aerodynamic term which describes when wings lose their lift.

It's a difficult balancing act.

"You don't want to hit the water too quickly or the plane will break into pieces", says first officer Tom Hanks of DHL, who flies Boeing 757s for the courier company.

At this point, a lot depends on the weather. In the seconds before impact, a pilot must try to ensure the wings are level - a feat clearly achieved by Captain Sullenberger, says David Learmount, operations and safety editor of Flight International magazine.

"[He] landed at precisely the right speed, completely under control, wings totally level. If one wing dips and catches the water, the aeroplane cartwheels, breaks up and some people would definitely have died."

The calmness of the Hudson river was a blessing in this case, compared with a choppy sea, says Mr Hanks.

"He could land anywhere as it wasn't rough water."

While keeping both wings horizontal the pilot must then lower the tail end. The nose would be at 12 degrees, which is higher than in a normal runway landing, and at the last minute the pilot would slowly lower the plane into the water.

Ideally, the aircraft would plane for a while before stopping, after which it would start to sink.

As Eric Moody, a former British Airways pilot, told the BBC, "you have to skim the surface like a pebble. If you go any other way; putting the tail or nose down too quickly, you're either going to break the plane in half or porpoise the thing, into the water and out."

Skill is a significant part of the process, observes Mr Hanks, but it's not the only requirement. "In terms of the actual impact on this occasion, [Capt Sullenberger] did a very good job, and he was also very lucky."

RELATED QUOTES:

I am only 92 years old, and have had a lot of experience flying off the water. Captain Sullenberger did an outstanding job of ditching and also a wonderful job of getting the passengers off with out any injuries. He is at the top of the list of airline pilots.

Captain MacKenzie Patterson, Carmel, California

I have always had a good chuckle during the pre-flight safety presentation on US domestic flights when the flight attendants review the procedures for a "water landing" as I always believed the term to be a euphemism for a crash landing. After this miraculous landing I'm going to stop chuckling and pay closer attention as it may save my life. Congratulations to Captain "Shelly" and the rest of the crew; they are truly heroes.

Bruce G, Falls Church, VA

What a fantastic display of skill the pilot displayed and his amazing ability to keep his head in such stressful situation, saving the lives of all passengers and crew, his heroic professionalism deserves major recognition. In these days of doom and gloom the news of this feat is so heartwarming.

Ken Lawler, Leyland, Lancashire.

Such skill and composure under pressure. You can see Capt Sullenberger had some military experience. I hope pilots like Mr Hanks can aspire to heroes like that.

William Poole, London

Isn't it great to hear about someone (with a splendid name) using their skill and competence to achieve something?

Ryan, Leeds, UK

Text taken from: http://news.bbc.co.uk/2/hi/uk_news/magazine/7833317.stm
Also suggested: http://news.bbc.co.uk/2/hi/americas/7834034.stm