How do you land a plane on water?
| WHO, WHAT, WHY? The Magazine answers... |
The plane, an Airbus A320, had been hit by a flock of birds shortly after taking off from the city's La Guardia airport, and then tried to go back before making an emergency landing in the river.
Captain Chesley Sullenberger III has been praised for his "masterful" landing, but how does a pilot attempt such a manoeuvre successfully?
Although the likelihood is remote, all commercial pilots must undergo training for such an eventuality before qualifying. There are taught to follow a procedure -which, in its initial stages is similar to an emergency landing on solid ground, although there may not be time in an emergency situation to follow it rigorously.
 | THE ANSWER  Plane must be slowed right down Both wings must be level with the water The tail is lower than normal The flatter the water the better |
Having made a mayday call and alerted the cabin crew, those in the cockpit must ensure the landing gear - wheels and undercarriage - is turned off 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 over 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 had already cut out.
As the aircraft nears the water, the pilot must try to continue slowing while, crucially, ensuring it does not "stall". In avionics 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.
Cartwheel
"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 maintaining both wings are equidistant from the nearing surface, the pilot must then lower the tail end. The nose would be higher than in a normal runway landing and at the last minute the pilot would slowly lower it 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."
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