As refined satellite data continues to offer more certainty that Malaysian Airlines Flight 370 was lost in the Southern Indian Ocean west of Perth, the US Navy has sent a “pinger locator” there to look for the black box of the downed Boeing 777.

A multinational effort is underway to locate objects spotted by search aircraft in the Southern Indian Ocean in an effort to locate the missing aircraft.

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As a precautionary measure in case a debris field is located, US Pacific Command assisted the Australian search authorities by sending a black box locator into the region

If a debris field is confirmed, its Towed Pinger Locator 25 will offer the search and rescue team a significant advantage in locating the missing Malaysian aircraft’s black box as it is able to locate aircraft down to a maximum depth of 20,000 feet anywhere in the world.

The Pinger Locator is towed behind a vessel at slow speeds, generally 1-5 knots, depending on the depth. The tow array carries a passive listening device for detecting pingers that automatically transmit an acoustic pulse.

“The Towed Pinger Locator has some highly sensitive listening capability so that if the wreck site is located, we can hear the black box pinger down to a depth of about 20,000 feet. Basically, this super-sensitive hydrophone gets towed behind a commercial vessel very slowly and listens for black box pings,” says Commander Chris Budde, US 7th Fleet operations officer.

Commercial aircraft pingers are mounted directly on the flight recorder, the recovery of which is critical to an accident investigation. If the search and rescue teams get anywhere near the aircraft wreckage, the acoustic signal of the pinger will be transmitted up the cable and presented audibly. The output can be fed through either an oscilloscope or a signal processing computer.

The operator monitors the greatest signal strength and records the navigation coordinates. This procedure is repeated on multiple track lines until the final position is triangulated. The system consists of the tow fish, tow cable, winch, hydraulic power unit, generator, and topside control console.

Most pingers transmit every second at 37.5 kHz, although the TPL can detect any pinger transmitting between 3.5 kHz and 50 kHz at any repetition rate.

If debris is found and positively confirmed as that from Flight 370, search and rescue efforts will be able to respond as quickly as possible since the battery life of the black box’s pinger is limited.

Even so, Scott Hamilton of Leeham News says caution needs to be raised about assumptions that these will reveal all there is to know about what happened on the flight.

“Assuming the Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR), therefore, were operational right up until the time of the crash of the airplane, there should be data recoverable if these units are eventually found. The FDR, being digital, has a 24 hour capacity and should provide a wealth of information. The CVR has only a two hour capacity and may yield much less, however,” says Hamilton.

“Clearly, it won’t reveal anything that happened over the Gulf of Thailand—this will have been overwritten by the end of MH370. But whether there is anything to be revealed on the last two hours for the flight is going to be uncertain.”

He says that in the US, by law the cockpit conversations recordings are only in 30 minute increments-the most recent 30 minutes. If this practice is true for other countries, including Malaysia, anything said in the cockpit as to what transpired when the aircraft originally was “lost” while still over the Gulf of Thailand will be lost. The final 30 minutes of cockpit conversation, and any noise from the cabin within “earshot” of the cockpit microphones, should however be retained on the CVR.

“Given the success, albeit two years after the crash, investigators had in recovering the FDR and CVR of Air France Flight 447 (the one that crashed into the South Atlantic in 2009, with main wreck recovered from around 12,000 ft), we feel reasonably confident MH370 will eventually be found and the recorders recovered. But manage your expectations about what might be found on the recorders,” says Hamilton who adds that in the US, pilots have the ability to erase the CVR once at the gate. “It’s certainly possible this occurred before MH370 went into the ocean,” he says.