NEW doubt has crept into the search for Malaysian Airlines flight MH370 after the Australian search agency said it would not make public the audio recordings of four acoustic “ping” signals.

After strong initial certainty they were hearing black box transmissions, the Joint Agency Coordination Centre headed by Angus Houston now appears less certain that they came from the plane.

“Analysis on all four detections is continuing,” said the JACC in a statement to News Corp Australia.

“The recordings of the detections will not be released at this point in time.”

RELATED: Captain Zaharie’s family defend his reputation

Retired Air Chief Marshall Houston had earlier said he could see no issue with releasing the audio, but that position has changed after six weeks of intense examination of the signals.

Questions are now being raised over the legitimacy of the two sets of pings, detected by the Ocean Shield’s towed-pinger locater on April 5 and 8, and why they need further analysis given they have already been subject to extensive scrutiny.

media_camera Mission commander ... Chief Coordinator of the Joint Agency Coordination Centre, Former Air Chief Angus Houston. Picture: Gary Ramage

And a new note of doubt yesterday crept into the JACC’s language.

“We continue to pursue this lead to either discount or confirm the area of the detections as the final resting place of MH370,” the JACC stated, noting that Mr Houston still believed the four signals were the most promising lead.

“At this point in time, it is too early to discount any of the acoustic detections.”

The four recordings, taken on April 5 and 8, were immediately sent to a secret facility at HMAS Albatross, in Nowra, NSW, called the Australian Joint Acoustic Analysis Centre.

One of the main purposes of the Nowra facility is to provide real-time feedback to Australian submarines that need instant analysis of potentially hostile frequencies.

Only days after the detections were first sent to the analysis centre, which stores a library of underwater sounds, Mr Houston said the transmissions had already been “analysed again and again”.

The international frequency standard for black boxes is 37.5kHz, and Mr Houston said an April 5 transmission was detected 33.331 kilohertz, pulsing at 1.106 second intervals.

Even though this was below 37.5kHz, it was an acceptable margin of error and Mr Houston was confident the pulsing was “identical” to an emergency beacon locator and likely from MH370.

media_camera Element of doubt ... Commander Joint Task Force 658, Commodore Peter Leavy, right, United States Navy Salvage Supervisor, Captain Mark Matthews, left, and ADV Ocean Shield RAN Mission Commander, Commander James Lybrand, centre, at a media conference in front of the Australian navy vessel Ocean Shield. Picture: Greg Wood

But last week, the Wall Street Journal quoted Australian naval officer Commander James Lybrand, as doubting that the second set of pings was from the plane’s cockpit voice recorder or flight data beacons.

The second transmissions from April 8 were at 27 kHz, and gave Commander Lybrand little confidence. “As far as frequency goes, between 33 kHz and 27 kHz is a pretty large jump,” he told the WSJ.

Mr Houston was asked on April 9 whether he would release some of the audio. “We’ll take a look at that. I don’t see why not,” he said at the time.

One possible reason for the JACC’s reluctance is that it would only cause more speculation from so-called experts. However, the mystery is already so awash with wild theories that its release would unlikely cause the searchers to lose focus.

But the fact that analysts were continuing to pore over the transmissions suggests they are reviewing earlier assumptions they did come from the jet’s black boxes.

Originally published as Doubt grows over MH370 ‘pings’