A robotic submarine deployed to search for the missing Malaysia Airlines plane in the southern Indian Ocean has had its first mission cut short. The Bluefin-21 was sent to search the sea floor for wreckage after signals believed to be consistent with "black box" flight recorders were detected. But the drone exceeded its operating limit of 4,500m (15,000ft) and was brought back to the surface.It was due to return later on Tuesday if weather conditions permitted." To account for inconsistencies with the sea floor, the search profile is being adjusted to extend the sonar search for as long as possible," an update from the US Navy – which operates the Bluefin-21 – said.
My perception: In order to bring a reason for changing in sea floor that caused the drone going more than expected depth of 4500m, search plan (search profile) is being optimized to extend the search limit of the sonar for going in depth as long as possible.