The lengthy search for the MH370 is far from over, even as the search supposedly narrows. ''We've had a fair bit of luck as well as great technical work,'' one expert involved in the search for the missing flight recorders of Malaysia Airlines flight MH370 said.

Experts indicate there are a number of steps in a deep sea search:

Phase 1 - Identifying where the aircraft hit water (completed): The analytical work done on the likely flight path of the doomed aircraft, using the last six pings from the plane to an Inmarsat satellite, combined with likely speed and glide time until it hit the water was used to narrow down the area to begin towing the pinger locator from Ocean Shield.

Phase 2 - Locating and identifying pings: With time running out on the batteries, this has assumed urgency. The Ocean Shield was lucky in picking up a ping on the second day along a possible arc 330 kilometres long. Several more pings have convinced searchers the signal is ''consistent with a black box recorder''. They are towing the ping locator to calculate location. In shallow water it is relatively easy to home in on the location as the distance the signal travels is not hugely affected by depth. In water more than 2000 metres deep, the signal direction is affected by the horizontal bearing and the depression angle.

British ship HMS Echo is assisting with hydrological information on the area. The aim is to reduce the search area as much as possible. Prime Minister Tony Abbott said on Friday it had been narrowed to ''within several kilometres'' but experts say the more it is narrowed, the better.

Phase 3 - Refining the search with an autonomous underwater vehicle: A remote operated submersible equipped with sonar will then begin a grid search of the area. But as the gear operates only to within two or three kilometres of the signal, the depth of the water will be critical. It will want to go as deep as the equipment allows and the signal is likely to be fading. That may take days or possibly weeks.

Phase 4 - Sending a camera-equipped submersible: The next stage would be photographing the wreckage and confirming the location of the black box. Investigators will want a full survey of the debris as it is an important clue to what happened.

Phase 5 -Retrieval of the black boxes: The flight data recorder is the most important, with thousands of data parameters from the plane recorded throughout its last flight and earlier ones as well. The cockpit voice recorder, a separate box, overwrites itself every two hours and will record the last two hours of conversation within the cockpit, if any.

Phase 6 - Recovery of wreckage. This phase could be very slow and expensive due to the depth of the water, harsh weather conditions and the distance from land.

The upshot is this will be a very long process. The experts are unlikely to say they have found the plane until they see photos or retrieve wreckage.