The Submarine Search for the Missing Jet Is Almost Done

No wreckage from missing Malaysia Airlines Flight 370 has been spotted by the unmanned submarine currently scouring the Indian Ocean seabed, despite 90% of the focused search area already having been examined and a search of the remaining fraction underway.

On Thursday, Bluefin-21 was deployed around 1,000 miles northwest of Perth, but the U.S.-made submersible has found nothing of interest.

Also on Thursday, yet another possible clue got discounted, as a metal object washed ashore on Australia’s west coast was examined and deemed not from the errant jet, adding to the hundreds of erroneous items spotted by satellite, plane and ship so far.

It has now been 48 days since the Boeing 777 disappeared en route from Kuala Lumpur to Beijing with 239 people on board.

“I’m just trying to reconcile the fact that we haven’t seen anything yet, but we heard those pings,” Jules Jaffe, of the Scripps Institution of Oceanography, tells TIME, referring to signals believed to have come from the black box data recorders of the missing plane. “The other hypothesis is that the debris field is quite large.”

Small pieces of wreckage spread over a large area will hamper investigators attempting to fathom what prompted the 11-year-old aircraft to go tragically off-course. Other than the black box flight and voice recorders, says Michael Daniel, an international aviation-safety consultant with more than three decades experience at the FAA, the “direction of the flaps, angles and controls, will show intent on how to land the aircraft.” Such clues may not be available if the plane hit the ocean hard and splintered into many fragments.

Assuming that the remaining Bluefin search proves fruitless, investigators will have to decide how best to proceed. Four pings were heard from the depths of the southern Indian Ocean. The current focused search area forms a 10 km-radius circle around the second of these pings, which has been deemed the most promising.

The decision to be made is whether to expand the search area incrementally from this same point, move to some of the other ping locations or reevaluate the entire operation. An answer is expected early next week after discussions between Angus Houston, the 66-year-old retired Australian Air Chief Marshall currently coordinating joint search operations, the Malaysian authorities and other stakeholders.

“Where they sensed the location of the pings and the strength of the pings, they’ll use different forms of triangulation and try to isolate a more probable area,” says Daniel. “It all helps but may not give a definitive answer for where the aircraft is.”

In any case, new assets will almost certainly be brought in to assist the hunt. The Remus 6000 is one possibility — this unmanned autonomous submarine first located doomed Air France Flight 447 in over 4 km-deep water of the Pacific Ocean, and has the ability to descend 2 km farther. But towed sonar locators, such as the Orion device operated by the U.S. Navy, many prove superior, as they can operate around the clock and provide real-time imagery without the laborious resurfacing and downloading of data. Certainly, says Jaffe, “The worst idea in the world is sticking a manned submersible down there because the target is so small [compared to the search area].”

On Thursday, up to 11 military aircraft and 11 ships were on hand to continue the hunt for debris. Air operations had been curtailed earlier in the week due to Tropical Cyclone Jack, and though it has now passed by the search zone, miserable conditions continue in its wake, with torrential rain, low cloud, winds up to 35 knots and sea swells of four meters, with visibility at just one kilometer.

As the hunt for MH370 enters yet another stage, already the most costly in aviation history, one certainty is that these fruitless forays will cease very shortly.