What happens to debris when a plane crashes in ocean?

Australia is leading the hunt for Malaysia Airlines flight MH370 which is thought to have gone down in the southern Indian Ocean, with experts in France due to examine Wednesday a wing part that washed up on La Reunion island.

The national science agency, CSIRO, along with the Australian Transport Safety Bureau, has performed drift modelling based on their current search zone for the jet that vanished last year en route from Kuala Lumpur to Beijing with 239 people on board.

Here are some of their insights released Wednesday:  

Q. What happens when a plane crashes into the ocean?

A. There is almost always some debris left floating after an aircraft crashes in water. The opportunity to locate and recover debris from the sea surface diminishes rapidly over the first few weeks from the time of a crash. Thereafter, some less permeable items of debris will remain afloat for a longer period but they will be increasingly dispersed.    

Q. What type of debris from a plane is likely to float?

A. Items designed to float include seat cushions, life jackets, escape slides. Many items from the cabin, such as cabin linings and tray tables, which are made of low density synthetic materials, can also remain buoyant. Similarly, aircraft structural components may entrap enough air to remain afloat for reasonable periods and have been commonly found on the water's surface following a crash.

Q. How long does debris stay afloat?

A. Over time, all floating debris will become waterlogged and then sink. For some items this may be relatively fast. For example, items which are buoyant due to entrapped air will sink when the air is released or void spaces become filled, a process which is hastened by the action of wind and waves. Other items constructed of materials which are less permeable, such as seat cushions, will float for long periods but they too will eventually sink when the material degrades through chemical and/or mechanical decomposition. This decomposition may take a very long time in the case of some synthetic materials, plastics in particular, but is quicker for items which biodegrade.

Q. Is it unusual for wreckage to wash ashore?

A. The opportunity to locate and recover debris from the sea surface diminishes rapidly over the first few weeks from the time of a crash. Thereafter, there will be some less permeable items of debris which will remain afloat for a longer period but they will be increasingly dispersed. Dispersal is directly related to the surface drift experienced by the individual items of debris, which in turn is related to their physical characteristics: size, shape and density. To be found ashore, an item of debris must remain afloat long enough and be subjected to the right combination of wind and currents for it to make landfall.   

Q. Could debris from MH370 have drifted 4,000 kilometres (2,500 miles) west from where the current search for the plane is underway in the southern Indian Ocean to the French territory of La Reunion Island?

A. Yes. The most recent drift modelling indicated that most debris from MH370 is likely to have drifted first north then west away from the probable accident site in the 16 months since the plane disappeared to July 2015. The drift analysis undertaken by the CSIRO further supports that the debris from MH370 may be found as far west of the search area as La Reunion Island.

Source: Australian Transport Safety Bureau and the Commonwealth Scientific and Industrial Research Organisation (CSIRO).