Mula-mula kita ketahui dulu apa kaitannya denyutan 37.5 kHz dan kotak hitam yang berwarna oren itu..
Kotak hitam, yang merekodkan semua data di dalam kapal terbang, adalah alat penting dalam penyiasatan kemalangan udara dan kerana kotak hitam, sembilan daripada sepuluh kemalangan dapat dijelaskan.
Pesawat komersil akan membawa dua kotak hitam. Perakam Digital Data Penerbangan mengandungi maklumat tentang kelajuan, ketinggian dan arah, manakala Perakam Suara Kokpit menjejaki perbualan kokpit dan bunyi dan pengumuman lain di dalam kabin juruterbang.
Ia sebenarnya berwarna oren ditambah dengan jalur putih agar ia mudah untuk dikesan. Setiap kotak hitam seberat tujuh hingga sepuluh kilogram (15-22 lb).
Diperkenalkan penggunaannya untuk penerbangan pada tahun 1960-an, perakam penerbangan diletakkan di dalam kotak besi agar ia dapat tahan lasak, elak dari kebakaran dan dapat bertahan di dalam air yang dalam.
Ia boleh bertahan sedalam 6,000 meter (hampir 20,000 kaki) di bawah air atau kepada suhu yang sangat panas iaitu 1,100 darjah selsius untuk satu jam. Ia dilengkapi dengan pengesan yang boleh mengeluarkan isyarat selama kira-kira satu bulan.
Isyarat itu kadang-kadang boleh berterusan selama beberapa hari selepas tempoh ini, kira-kira lapan hingga 10 hari, menurut ketua misi carian Australia, Angus Houston.
Frekuensi 37.5 kHz adalah denyutan yang paling biasa untuk perakam data penerbangan, menurut pakar .
Ia adalah tahap yang sama di mana isyarat yang dikesan oleh kapal Cina Haixun 01 pada 5 April ketika pencarian dilakukan di selatan Lautan Hindi untuk mencari pesawat MH370 yang hilang.
Kotak hitam dapat dikesan dalam purata dua kilometer (1.2 batu).
Perairan dimana kapal China melakukan pencarian adalah 4.5 kilometer (hampir tiga batu) dalam.
Jadi, walaupun isyarat didapati datang dari pesawat namun kerja mencari tetap akan menjadi satu cabaran, kata Houston.
Pada Januari 2004 kotak hitam penerbangan Mesir yang terhempas di perairan Sharm el-Sheikh ditemui selepas carian dua minggu, 1,022 meter di bawah air.
Pada bulan Mei 2011, selepas 23 bulan tenggelam pada kedalaman 3,900 meter di Lautan Atlantik, kotak hitam penerbangan Air France AF447 berjaya ditemui dengan data yang masih utuh.
Ini dapat membantu penyiasat untuk menentukan punca kemalangan yang berlaku pada 1 Jun 2009 ~ Astro Awani
Berikut adalah laporan tentang Kapal milik Australia 'Ocean Shield' telah mengesan isyarat tersebut..
Australian ship HMAS Ocean Shield has twice detected signals from the black box of the missing Malaysia Airlines flight MH370, in what authorities believe is the most promising lead since the month-long search operation was launched.
The head of the Joint Agency Coordination Centre in Perth, Angus Houston, in announcing the possible breakthrough this afternoon, said the first pinger signal lasted two hours 20 minutes.
A second instance lasting 13 minutes showed two distinct pinger returns were audible, he said. "Clearly this is the most promising lead, and probably in the search so far, it is probably the best information that we have had," he said.
The first detection held for 2.5 hours before the ship lost contact, after turning around, the ship picked up the signal for around 13 minutes, he said. "On this occasion, two distinct pinger returns were audible," Houston said.
"Significantly, this would be consistent with transmissions from both the flight data recorder and the cockpit voice recorder."
Confirmation of whether the signals were emitted from the Kuala Lumpur-to-Beijing-bound plane, missing since March 8 with 239 people on board, could take several days, Houston said.
The black boxes, thought be to lying on the ocean floor, are equipped with locator beacons that send pings but the beacons' batteries are thought to be running out of charge by now, a month after flight MH370 disappeared.
The United States navy "pinger locator" connected to the Australian ship Ocean Shield was trawling an area some 300 nautical miles away from separate reports by Chinese patrol ship Haixun 01 of a pulse signal with the same frequency of a black box.
If the signals can be narrowed further, an unmanned underwater vehicle, Bluefin 21, will be sent to attempt to locate wreckage on the sea floor to verify the signals, said Houston, who noted that the potential search area was 4.5km deep, the same as the Bluefin range.
"We are right on the edge of capability and we might be limited on capability if the aircraft ended up in deeper water," he said.
"In very deep oceanic water, nothing happens fast." He said that while Ocean Shield continued to trawl the area to try to regain contact, search teams were also investigating the reports by the Chinese ship several hundred kilometres away ~ The Malaysian Insider