Looking at past accidents, 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. 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.
The most recent drift modelling indicated that the net drift of most debris in the sixteen months to July 2015 is likely to have been north and then west away from the accident site. 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 Réunion Island.
This is consistent with the currently defined search area.