法国航空失事客机搜救行动

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More than a week after the air crash, the first of the bodies retrieved from the Atlantic are back on dry land. 228 passengers and crew perished in the disaster; only a small fraction of that number has so far been found by the search teams.

Why the Air France Airbus plunged from the skies is still unclear. But one possibility is gaining credence.

The early theories around what caused the Air France crash are centred on one of these, a Pitot tube, on whether or not it was working when the aircraft flew into a storm. But what is it, what does it do, and how does it work?

"As [for] a Pitot tube, all aircraft must have some system of measuring airspeed at various altitudes. This, all aircraft have this type of tube which measures the speed of dynamic pressure going in through here and because true airspeed changes with altitude, it measures the static pressure through these pipes. The difference between those two gives you an indication of airspeed which is fed through into the cockpit either on an airspeed indicator, or in modern Airbus type or Boeing type of aircraft, then it feeds through to the computer. If for any reason, these get blocked or they give a false reading, then the aircraft is looking at a false reading of speed."

Pilots who fly for Air France are urging the airline to change all their Pitot tube airspeed sensors on Airbus planes immediately.

"We are not trying to replace the official investigation which is going to take a long time. But we are saying that apparently the sensors are probably responsible. So we are saying that Air France should err on the side of caution."

The British Airline Pilots Association says it has no fears over the safety of the Airbuses flown by British airlines.

In the fullest of time, we will find out what happened to Flight AF447. But for now, this is a human tragedy for so many families, not least the Schnabls. They were all heading for Paris from Brazil, but flew on two separate planes: father and daughter took one flight; mother and son another. It was they who chose AF447.

David Bowden, Sky News.

Glossary [only for reference]

retrieve [transitive]: formal; to find something and bring it back

perish [intransitive]: formal or literary; to die, especially in a terrible or sudden way

fraction [countable]: a very small amount of something

 plunge [intransitive]: to move, fall, or be thrown suddenly forwards or downwards

gain credence: to become more widely accepted or believed

theory [countable]: an idea or opinion that someone thinks is true but for which they have no proof

centre on/upon something [phrasal verb]: if your attention centres on something or someone, or is centred on them, you pay more attention to them than anything else

Pitot tube: a pressure measurement instrument used to measure fluid flow velocity. The pitot tube was invented by the French engineer Henri Pitot in the early 1700s.

as for somebody/something: used when you are starting to talk about someone or something new that is connected with what you were talking about before

airspeed [singular, uncountable]: the speed at which a plane travels

cockpit [countable]: the area in a plane, small boat, or racing car where the pilot or driver sits

airspeed indicator (or airspeed gauge): an instrument used in an aircraft to display the craft's airspeed, typically in knots, to the pilot.

 feed [transitive]: to put information into a computer over a period of time

err on the side of something: to be more careful or safe than is necessary, in order to make sure that nothing bad happens

British Air Line Pilots' Association (BALPA): the second largest flight crew association within IFALPA (International Federation of Air Line Pilots’ Associations). It was founded on 27 June 1937 by Eric Lane-Burslem and 87 other pilots at a meeting at the Greyhound Hotel in Croydon. Today, it has more than 75% of British civil and commercial pilots as members.

not least: formal; used to emphasize that something is important