The search for missing Malaysian airliner MH370 began afresh in a new area last year.  I wrote about it for The Economist at the time (see here). It has been reported today that debris consisting of a wing part and, possibly, a suitcase that may have come from the plane has washed up on Reunion island, thousands of miles away in the Indian Ocean near Madagascar. Ocean current data suggest it is possible the items could have travelled from the area currently being searched since March 8th 2014 when the plane disappeared.

But as I researched the story last year I developed a nagging doubt about the new area to be searched, for two reasons. First, as it was based largely on satellite data there were many assumptions, extrapolations and margins for error. The technology seemed to point to a very small part of a very large ocean and I wondered if it really could be that accurate. As the latest Operational Search Update from the Australian Joint Agency Coordination Centre makes clear, my concerns may not have been unfounded. The search area announced last year with much publicity was doubled in size to 120,000 square kilometres in April.

That is not to suggest the debris that has come ashore in Reunion is not from MH370, just that the plane may have come down in an area that has yet to be searched, and possibly not in the Southern Ocean at all. Which leads to the second cause of my apprehension.

As a document released last June by the Australian Transport Safety Bureau shows (on page 40), two low-frequency hydro-acoustic signals recorded at the likely time of MH370’s demise raise an intriguing question. The two signals came from underwater hydrophones used by a monitoring station listening out for violations of the United Nations Nuclear Weapons Test Ban and a Marine Observation System. An underwater event occurred that the document states “could be associated with the impact of the aircraft on the water or with the implosion of wreckage as the aircraft sank”. (It also acknowledges that a “small earth tremor” could be responsible.) But because satellite data were believed to offer a more accurate answer, the signals from the two stations – that suggested a crash site in the middle of the Indian Ocean due south of Sri Lanka – was discounted. Dr Alec Duncan, the head of the team investigating the underwater acoustic event said “the crash of a large aircraft in the ocean would be a high energy event and [would be] expected to generate intense underwater sounds” (images from the team showing the acoustic results and likely point of origin can be seen here).

So, the debris may show that MH370 impacted with the water, which will scotch some of the more outlandish conspiracy theories but be of little consolation to the grieving families. Dr Duncan says that he has many other underwater recorders that may have picked up similar signals to the two already examined. They have yet to be recovered. In the absence of any other evidence as to the location of the missing plane, these additional hydrophone data will be of great interest when eventually recovered.