An Australian ship scouring the Indian Ocean for missing flight MH370 has detected two further pings consistent with the plane's two black boxes, in a "great lead", bolstering hopes for wreckage discovery. 
 
 The Australian Defence Vessel Ocean Shield, towing a US pinger locator, detected two sets of pings, on Tuesday afternoon and then again about five hours later. 
 
 The signal detected on Tuesday afternoon was held for about five minutes and 32 seconds; followed by a second signal on Tuesday night, which was held for seven minutes. 
 
 The Australian vessel Ocean Shield is towing a pinger locator in the search for MH370. Photo: AP 
 
 The development came more than two days after Ocean Shield first detected the month-long search's most promising lead: two acoustic events on Saturday. 
 
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 Retired air chief marshal Angus Houston, the head of the search's Joint Agency Co-ordination centre, announced the "promising" development during a press conference in Perth on Wednesday afternoon. 
 
 It revives hope the missing Malaysia Airlines plane's black box is still transmitting data days after its batteries were due to run dead. 
 
 Crew on the Ocean Shield deploy the towed pinger locator. Photo: AP 
 
 Mr Houston said expert data analysis on previously detected signals had found they were not of natural origin, further boosting hopes of a breakthrough. 
 
 Mr Houston said experts believed the signals were consistent with those of a flight data recorder. 
 
 He said the first two pings - detected on April 5 at 4.45pm and at 9.27pm Perth time - had been analysed by the Australasian Joint Acoustic Analysis Centre, based at HMAS Albatross in Nowra, on the NSW south coast. 
 
 "The analysis determined that a very stable, distinct and clear signal was detected at 33.331 kilohertz, and that it consistently pulsed at a 1.106-second interval," Mr Houston said. 
 
 ''They therefore asses that the transmission was not of natural origin, and was likely sourced from specific electronic equipment. They believe the signals to be consistent with the specification and description of a flight data recorder.'' 
 
 He said two latest pings were detected on Tuesday - at 4.27pm and 10.17pm, Perth time. 
 
 Mr Houston said up to 11 military aircraft, four civil aircraft and up to 14 ships would assist in Wednesday's search, while the Ocean Shield would also conduct a sonar voice search. 
 
 The search area has been refined to a single zone, about 75,423 square kilometres in size, 2261 kilometres north west of Perth, which was a considerably smaller area than in previous days, he said. 
 
 ''Based on Ocean Shield's detections, we are now searching a much more concentrated area, based on the drift predications made possible by Ocean Shield's detections,'' Mr Houston said. 
 
 ''The smaller area has also allowed us to plan much tighter search patterns based entirely on visual search principles. In other words, we have intensified our search in the visual search area. 
 
 "There's no second chances," he said. 
 
 "It looks like the signals we picked up recently have been much weaker than the original signals we picked up ... we're either a long away from it or in my view more likely the batteries are starting to fade." 
 
 Although authorities have previously said the autonomous underwater vehicle Bluefin-21 would be dropped to the ocean floor once they received a third ping, they have yet to deploy the asset. 
 
 "By triangulating this data we will be able to come up with a much smaller search area under water," Mr Houston said. 
 
 "Time spent on the surface, we're covering six times more area than we would be able to do when we get under water. With the batteries due to fail shortly, we need to get as much positional data as we can." 
 
 An RAAF aircraft has been diverted to Ocean Shield to drop buoys around the field to lay a "sonar buoy pattern", which will involve underwater and floating components transmitting data back to the aircraft. 
 
 "That will provide a range of sensors, 1000 feet down, which is 1000 feet closer to the pinger locator on the ocean floor," Commodore Leavy, the operational head of the Australian search, said. 
 
 The Malaysia Airlines Boeing 777 vanished without a trace during en route to Beijing from Kuala Lumpur on March 8. 
 
 Despite an extensive and costly international search operation off the West Australian coast, the effort has failed to turn up a single piece of evidence to confirm the plane's final resting place. 
 
 
 
 ||||| Story highlights U.S. official: "We need to maintain respectful optimism and be responsible" 
 
 Expert says refined search area manageable for underwater vessels 
 
 Possible discovery of plane's pingers energizes search, but for how much longer? 
 
 Agency: Up to 15 planes, 14 ships could take part in Wednesday's search 
 
 In a sea of uncertainty, two bits of good news emerged Wednesday. 
 
 The Australian ship Ocean Shield picked up fresh signals that officials hope are locator beacons from the data recorders of the missing Malaysia Airlines Flight 370. 
 
 The ship had first picked up the underwater pulses Saturday. But then, for the next three days, nothing. 
 
 On Tuesday, the ship once again reacquired the signals. That's four signals in the same broad area: two on Saturday; two on Tuesday. 
 
 Just Watched Search area narrows despite no new pings replay More Videos ... Search area narrows despite no new pings 01:16 PLAY VIDEO 
 
 Just Watched Could the pings be from MH370? replay More Videos ... Could the pings be from MH370? 02:07 PLAY VIDEO 
 
 Just Watched Hear possible 'ping' detected in search replay More Videos ... Hear possible 'ping' detected in search 00:40 PLAY VIDEO 
 
 Photos: The search for Malaysia Airlines Flight 370 106 photos Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A policewoman watches a couple whose son was on board the missing Malaysia Airlines Flight 370 cry outside the airline's office building in Beijing after officials refused to meet with them on Wednesday, June 11. The jet has been missing since March 8. Hide Caption 1 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Members of the media scramble to speak with Azharuddin Abdul Rahman, director general of Malaysia's Civil Aviation Department, at a hotel in Kuala Lumpur, Malaysia, on Tuesday, May 27. Data from communications between satellites and missing Malaysia Airlines Flight 370 was released Tuesday, more than two months after relatives of passengers say they requested that it be made public. Hide Caption 2 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – This photo illustration shows a journalist looking on the data communication logs from British satellite operator Inmarsat. Malaysian authorities have published the 47-page document containing hundreds of lines of communication logs between the jetliner and Inmarsat's satellite system. Hide Caption 3 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Relatives of Chinese passengers who were on Malaysia Airlines Flight 370 listen to part of the audio communications between Flight 370's cockpit and air traffic controllers during a meeting with Malaysian officials Wednesday, April 30, in Beijing. Hide Caption 4 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – An autonomous underwater vehicle is brought back aboard the Australian ship Ocean Shield after a search mission for the flight Saturday, April 19, in the southern Indian Ocean. Hide Caption 5 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A Royal Malaysian Air Force plane takes off from an airbase near Perth, Australia, to help in the search on Thursday, April 17. Hide Caption 6 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Operators aboard the Australian ship Ocean Shield move Bluefin-21, the U.S. Navy's autonomous underwater vehicle, into position to search for the jet on Monday, April 14. Hide Caption 7 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A member of the Royal New Zealand Air Force looks out of a window while searching for debris off the coast of western Australia on Sunday, April 13. Hide Caption 8 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – British Royal Navy sailors aboard the vessel HMS Echo take part in the search for the jet on April 13. Hide Caption 9 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Crew members aboard the Echo watch a smaller boat that's part of the British search effort on April 13. Hide Caption 10 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – The Echo moves through the waters of the southern Indian Ocean. Hide Caption 11 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A map provided Saturday, April 12, details efforts to find the missing jet. Hide Caption 12 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Chinese navy personnel head out on a boat to the Royal Australian Navy ship HMAS Success on Wednesday, April 9. Hide Caption 13 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A Royal Australian Air Force AP-3C Orion, on a mission to drop sonar buoys to assist in the search, flies past the Australian vessel Ocean Shield on April 9. Hide Caption 14 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A relative of a missing passenger cries at a vigil in Beijing on Tuesday, April 8. Hide Caption 15 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A member of the Royal Australian Air Force walks toward a plane that just arrived in Perth on April 8. Hide Caption 16 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Australian Defense Force divers scan the water for debris Monday, April 7, in the southern Indian Ocean. Hide Caption 17 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A towed pinger locator is readied to be deployed April 7 off the deck of the Australian vessel Ocean Shield. Hide Caption 18 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Capt. Mark Matthews of the U.S. Navy talks to reporters in Perth about the search on April 7. Hide Caption 19 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A member of the search operation points to a map outlining search areas during a news conference April 7 in Perth. Hide Caption 20 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A U.S. Navy airplane takes off from Perth to assist in the search on April 7. Hide Caption 21 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A member of the Royal New Zealand Air Force looks at a flare in the Indian Ocean during search operations on Friday, April 4. Hide Caption 22 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Members of the Royal New Zealand Air Force monitor data April 4 on board an aircraft during search operations. Hide Caption 23 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A relative of a Flight 370 passenger watches television in a Beijing hotel as he awaits new information about the missing plane on Thursday, April 3. Hide Caption 24 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Another relative of a Flight 370 passenger waits for updates in Beijing on Wednesday, April 2. Many families have criticized the Malaysian government's handling of information in the plane's disappearance. Hide Caption 25 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A member of the Japanese coast guard points to a flight position data screen while searching for debris from the missing jet on Tuesday, April 1. Hide Caption 26 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Kojiro Tanaka, head of the Japanese coast guard search mission, explains the efforts en route to the search zone April 1. Hide Caption 27 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A woman prepares for an event in honor of those aboard Flight 370 on Sunday, March 30, in Kuala Lumpur, Malaysia. Hide Caption 28 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – An underwater search-surveying vehicle sits on the wharf in Perth, ready to be fitted to a ship to aid in the search for the jet. Hide Caption 29 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A girl in Kuala Lumpur writes a note during a ceremony for the missing passengers on March 30. Hide Caption 30 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A teary-eyed woman listens from the back as other relatives of Flight 370 passengers speak to reporters March 30 in Subang Jaya, Malaysia. Dozens of anguished Chinese relatives demanded that Malaysia provide answers to the fate of those on board. Hide Caption 31 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – An object floating in the southern Indian Ocean is seen from a Royal New Zealand Air Force P-3K2 Orion aircraft searching for the missing jet on Saturday, March 29. Ships participating in the search retrieved new debris Saturday, but no objects linked to the missing plane, according to Australian authorities. Hide Caption 32 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A Royal New Zealand Air Force member launches a GPS marker buoy over the southern Indian Ocean on March 29. Hide Caption 33 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – The sole representative for the families of Flight 370 passengers leaves a conference at a Beijing hotel on Friday, March 28, after other relatives left en masse to protest the Malaysian government's response to their questions. Hide Caption 34 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A member of the Royal Australian Air Force is silhouetted against the southern Indian Ocean during the search for the missing jet on Thursday, March 27. Hide Caption 35 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Flight Lt. Jayson Nichols looks at a map aboard a Royal Australian Air Force aircraft during a search on March 27. Hide Caption 36 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – People in Kuala Lumpur light candles during a ceremony held for the missing flight's passengers on March 27. Hide Caption 37 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Crew members of the Chinese icebreaking ship Xuelong scan the Indian Ocean during a search for the missing jet on Wednesday, March 26. Hide Caption 38 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – People work at a console at the British satellite company Inmarsat on Tuesday, March 25, in London. Hide Caption 39 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – The mother of a passenger who was on Malaysia Airlines Flight 370 cries at her home in Medan, Indonesia, on March 25. Hide Caption 40 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Australian Defense Minister David Johnston speaks to the media March 25 about the search for the missing jet. Hide Caption 41 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A family member of a missing passenger reacts after hearing the latest news March 25 in Kuala Lumpur. Hide Caption 42 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Angry relatives of those aboard Malaysia Airlines Flight 370 react in Beijing on Monday, March 24, after hearing that the plane went down over the southern Indian Ocean, according to analysis of satellite data. Hide Caption 43 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Grieving relatives of missing passengers leave a hotel in Beijing on March 24. Hide Caption 44 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Malaysian Prime Minister Najib Razak, center, delivers a statement about the flight March 24 in Kuala Lumpur. Razak's announcement came after the airline sent a text message to relatives saying it "deeply regrets that we have to assume beyond any reasonable doubt that MH 370 has been lost and that none of those onboard survived." Hide Caption 45 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Relatives of the missing passengers hold a candlelight vigil in Beijing on March 24. Hide Caption 46 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A member of the Royal Australian Air Force looks out an aircraft during a search for the missing jet March 24. Hide Caption 47 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A woman reads messages for missing passengers at a shopping mall in Kuala Lumpur on March 24. Hide Caption 48 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Flight Lt. Josh Williams of the Royal Australian Air Force operates the controls of an AP-3C Orion on Sunday, March 23, after searching the southern Indian Ocean. Hide Caption 49 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Ground crew members wave to a Japanese Maritime Defense Force patrol plane as it leaves the Royal Malaysian Air Force base in Subang, Malaysia, on Sunday, March 23. The plane was heading to Australia to join a search-and-rescue operation. Hide Caption 50 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A passenger views a weather map in the departures terminal of Kuala Lumpur International Airport on Saturday, March 22. Hide Caption 51 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A Chinese satellite captured this image, released on March 22, of a floating object in the Indian Ocean, according to China's State Administration of Science. It is a possible lead in the search for the missing plane. Surveillance planes are looking for two objects spotted by satellite imagery in remote, treacherous waters more than 1,400 miles from the west coast of Australia. Hide Caption 52 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A member of the Royal Australian Air Force looks down at the Norwegian merchant ship Hoegh St. Petersburg, which took part in search operations Friday, March 21. Hide Caption 53 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – The Royal Australian Air Force's Neville Dawson, left, goes over the search area with Brittany Sharpe aboard an AP-3C Orion some 2,500 kilometers (about 1,500 miles) southwest of Perth, Australia, over the Indian Ocean on March 21. Hide Caption 54 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Satellite imagery provided by the Australian Maritime Safety Authority on Thursday, March 20, shows debris in the southern Indian Ocean that could be from Flight 370. The announcement by Australian officials that they had spotted something raised hopes of a breakthrough in the frustrating search. 
 
 Hide Caption 55 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A closer look at the satellite shot of possible debris from Malaysia Airlines Flight 370. Hide Caption 56 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Another satellite shot provided by the Australian Maritime Safety Authority shows possible debris from the flight. Hide Caption 57 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A closer look at the satellite shot of possible debris. Hide Caption 58 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – The Australian Maritime Safety Authority's John Young speaks to the media in Canberra, Australia, on March 20 about satellite imagery. Hide Caption 59 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A distraught relative of a missing passenger breaks down while talking to reporters at Kuala Lumpur International Airport on Wednesday, March 19. Hide Caption 60 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A relative of missing passengers waits for a news briefing by officials in Beijing on Tuesday, March 18. Hide Caption 61 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A relative of a missing passenger tells reporters in Beijing about a hunger strike to protest authorities' handling of information about the missing jet. Hide Caption 62 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A member of Indonesia's National Search and Rescue Agency joins in a search for the missing plane in the Andaman 
 
 Sea area around the northern tip of Indonesia's Sumatra on Monday, March 17. Hide Caption 63 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Relatives of missing passengers watch a news program about the missing plane as they await information at a hotel ballroom in Beijing on March 17. Hide Caption 64 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Malaysian Transportation Minister Hishamuddin Hussein, center, shows maps of the search area at a hotel next to the Kuala Lumpur International Airport on March 17. Hide Caption 65 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – U.S. Navy crew members assist in search-and-rescue operations Sunday, March 16, in the Indian Ocean. Hide Caption 66 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Indonesian personnel watch over high seas during a search operation in the Andaman Sea on Saturday, March 15. Hide Caption 67 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A foam plane, which has personalized messages for the missing flight's passengers, is seen at a viewing gallery March 15 at Kuala Lumpur International Airport. Hide Caption 68 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A member of the Malaysian navy makes a call as his ship approaches a Chinese coast guard ship in the South China Sea on March 15. Hide Caption 69 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A Indonesian ship heads to the Andaman Sea during a search operation near the tip of Sumatra, Indonesia, on March 15. Hide Caption 70 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Elementary school students pray for the missing passengers during class in Medan, Indonesia, on March 15. Hide Caption 71 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Col. Vu Duc Long of the Vietnam air force fields reporters' questions at an air base in Ho Chi Minh City, Vietnam, after a search operation on Friday, March 14. Hide Caption 72 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Members of the Chinese navy continue search operations on Thursday, March 13. The search area for Flight 370 has grown wider. After starting in the sea between Malaysia and Vietnam, the plane's last confirmed location, efforts are expanding west into the Indian Ocean. Hide Caption 73 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A Vietnamese military official looks out an aircraft window during search operations March 13. Hide Caption 74 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Malaysian air force members look for debris on March 13 near Kuala Lumpur. Hide Caption 75 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A relative of a missing passenger watches TV at a Beijing hotel as she waits for the latest news March 13. Hide Caption 76 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A member of the Indonesian National Search and Rescue Agency scans the horizon in the Strait of Malacca on Wednesday, March 12. Hide Caption 77 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Relatives of missing passengers wait for the latest news at a hotel in Beijing on March 12. Hide Caption 78 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Journalists raise their hands to ask questions during a news conference in Sepang on March 12. Hide Caption 79 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Indonesian air force officers in Medan, Indonesia, examine a map of the Strait of Malacca on March 12. Hide Caption 80 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A member of the Vietnamese air force checks a map while searching for the missing plane on Tuesday, March 11. Hide Caption 81 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Iranians Pouri Nourmohammadi, second left, and Delavar Seyed Mohammad Reza, far right, were identified by Interpol as the two men who used stolen passports to board the flight. But there's no evidence to suggest either was connected to any terrorist organizations, according to Malaysian investigators. Malaysian police believe Nourmohammadi was trying to emigrate to Germany using the stolen Austrian passport. Hide Caption 82 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – An Indonesian navy crew member scans an area of the South China Sea bordering Indonesia, Malaysia and Thailand on Monday, March 10. Hide Caption 83 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Vietnam air force Col. Le Huu Hanh is reflected on the navigation control panel of a plane that is part of the search operation over the South China Sea on March 10. Hide Caption 84 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Relatives of the missing flight's passengers wait in a Beijing hotel room on March 10. Hide Caption 85 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A U.S. Navy Seahawk helicopter lands aboard the USS Pinckney to change crews before returning to search for the missing plane Sunday, March 9, in the Gulf of Thailand. Hide Caption 86 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Members of the Fo Guang Shan rescue team offer a special prayer March 9 at Kuala Lumpur International Airport. Hide Caption 87 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A handout picture provided by the Malaysian Maritime Enforcement Agency shows personnel checking a radar screen during search-and-rescue operations March 9. Hide Caption 88 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Italian tourist Luigi Maraldi, who reported his passport stolen in August, shows his current passport during a news conference at a police station in Phuket island, Thailand, on March 9. Two passengers on the missing Malaysia Airlines flight were reportedly traveling on stolen passports belonging to Maraldi and an Austrian citizen whose papers were stolen two years ago. Hide Caption 89 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Hugh Dunleavy, commercial director of Malaysia Airlines, speaks to journalists March 9 at a Beijing hotel where relatives and friends of the missing flight's passengers are staying. Hide Caption 90 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Vietnamese air force crew stand in front of a plane at Tan Son Nhat airport in Ho Chi Minh City on March 9 before heading out to the area between Vietnam and Malaysia where the airliner vanished. Hide Caption 91 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Buddhist monks at Kuala Lumpur International Airport offer a special prayer for the missing passengers on March 9. Hide Caption 92 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – The Chinese navy warship Jinggangshan prepares to leave Zhanjiang Port early on March 9 to assist in search-and-rescue operations for the missing Malaysia Airlines flight. The Jinggangshan, an amphibious landing ship, is loaded with lifesaving equipment, underwater detection devices and supplies of oil, water and food. Hide Caption 93 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Members of a Chinese emergency response team board a rescue vessel at the port of Sanya in China's Hainan province on March 9. The vessel is carrying 12 divers and will rendezvous with another rescue vessel on its way to the area where contact was lost with Malaysia Airlines Flight 370. Hide Caption 94 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – The rescue vessel sets out from Sanya in the South China Sea. Hide Caption 95 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A family member of missing passengers is mobbed by journalists at Kuala Lumpur International Airport on Saturday, March 8. Hide Caption 96 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A Vietnamese air force plane found traces of oil that authorities had suspected to be from the missing Malaysia Airlines plane, the Vietnamese government online newspaper reported March 8. However, a sample from the slick showed it was bunker oil, typically used to power large cargo ships, Malaysia's state news agency, Bernama, reported on March 10. Hide Caption 97 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Malaysian Prime Minister Najib Razak, center, arrives to meet family members of missing passengers at the reception center at Kuala Lumpur International Airport on March 8. Hide Caption 98 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Malaysia Airlines official Joshua Law Kok Hwa, center, speaks to reporters in Beijing on March 8. Hide Caption 99 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A relative of two missing passengers reacts at their home in Kuala Lumpur on March 8. Hide Caption 100 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Wang Yue, director of marketing of Malaysia Airlines in China, reads a company statement during a news conference at the Metro Park Lido Hotel in Beijing on March 8. Hide Caption 101 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Chinese police at the Beijing airport stand beside the arrival board showing delayed Flight 370 in red on March 8. Hide Caption 102 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A woman asks a staff member at the Beijing airport for more information on the missing flight. Hide Caption 103 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – A Malaysian man who says he has relatives on board the missing plane talks to journalists at the Beijing airport on March 8. Hide Caption 104 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Passengers walk past a Malaysia Airlines sign on March 8 at Kuala Lumpur International Airport. Hide Caption 105 of 106 Photos: The search for Malaysia Airlines Flight 370 106 photos The search for Malaysia Airlines Flight 370 – Malaysia Airlines Group CEO Ahmad Juahari Yahya, front, speaks during a news conference on March 8 at a hotel in Sepang. "We deeply regret that we have lost all contacts" with the jet, he said. Hide Caption 106 of 106 EXPAND GALLERY 
 
 Just Watched What you need to know about a black box replay More Videos ... What you need to know about a black box 01:51 PLAY VIDEO 
 
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 "I believe we are searching in the right area but we need to visually identify wreckage before we can confirm with certainty that this is the final resting place of MH370," Houston said. 
 
 The second piece of good news? Authorities analyzed the signals picked up Saturday and determined they were not of 
 
 natural origin and was likely sourced from specific electronic equipment. 
 
 "They believe the signals to be consistent with the specification and description of a flight data recorder," Houston said. 
 
 Signals getting weaker 
 
 Wednesday is Day 33 in the search for Malaysia Airlines Flight 370, which went missing March 8. It was carrying 239 people. 
 
 Authorities haven't given up trying. Instead, they are pinning their hopes on the so-pings. 
 
 But time is not on their side. 
 
 The batteries powering the flight recorders' locator beacons are certified to be working for 30 days. Stored in a plane's tail, they are designed to begin sending off distinct, high-pitched signals as soon as they come in contact with water. 
 
 "The signals are getting weaker. Which means we're either moving away from the search area or the pinger batteries are dying," Houston said. 
 
 The first signal, at 4:45 p.m. Perth Time on Saturday, lasted 2 hours 20 minutes. 
 
 The second, at 9:27 p.m. Saturday, lasted 13 minutes. 
 
 The third signal was picked up Tuesday at 4:27 p.m. That lasted 5 minutes 32 seconds. 
 
 The fourth, at 10:17 p.m. Tuesday, was 7 minutes long. 
 
 "It's certainly encouraging that more signals have been detected," Pentagon spokesman Adm. John Kirby told CNN. 
 
 "There is still much work to do, however." 
 
 Four reasons to believe; six reasons to doubt 
 
 Discovery of possible 'locator beacon' pulses gives hope 
 
 Wednesday's search includes up to 11 military planes, four civilian aircraft as well as 14 ships -- three of which, Australia's Ocean Shield further north and the British HMS Echo and Chinese Haixun 01 to the south -- will be focusing underwater. 
 
 All told, everyone involved will be scouring a 29,000-square-mile zone centered about 1,400 miles northwest of Perth, according to Australia's Joint Agency Coordination Centre. That's large and challenging, but still pales in comparison to the once nearly 3 million miles, at sea and on land, the searchers were scouring for signs of the lost aircraft a few weeks ago. 
 
 Kevin McEvoy, a New Zealand air force commodore involved in the effort, noted that authorities once "didn't even know which haystack" to look in for the aircraft. 
 
 "I think we have got a much clearer picture around the areas that we need to concentrate on," McEvoy told CNN's Erin Burnett from Auckland. 
 
 Authorities greatly shrank that area after analyzing satellite data to determine Flight 370 had set off from Kuala Lumpur toward Beijing, turned around to go back over the Malay Peninsula, then ended up in the southern Indian Ocean. 
 
 Why? No one really knows. 
 
 The best chance to answer that question may rest wherever the plane -- and its so-called black boxes, with their trove of information about the plane and its movements -- now resides. 
 
 Search planes dispatched day after day looking for evidence of the missing airliner -- a floating wing, a seat cushion, anything -- thus far have come up empty. 
 
 The latest, greatest hopes have come from crews listening underwater for signs of Flight 370. 
 
 The first such possible breakthrough came last Friday and Saturday, when a Chinese ship detected pulses that may have been from the plane. No more have been heard since. 
 
 According to McEvoy, "the main focus" centers around the site of Saturday's discovery from Australia's Ocean Shield. It used more advanced detection gear than that aboard the Chinese vessel and was found some 375 miles away, leading Houston to believe they are separate signals. 
 
 The first signal, detected by a towed pinger locator, persisted for more than two hours; a second went on for about 13 minutes. 
 
 Tuesday afternoon, it lasted about 5 minutes and 32 seconds. Tuesday night, about seven minutes. 
 
 Beyond the dwindling battery life, there's all the ocean to contend with: The Ocean Shield signals were in water about 2.6 miles deep, meaning a number of things could literally get in the way of or otherwise disrupt the pulses. 
 
 Searchers' intent not to roil the waters any further is why air and seaborne traffic in that find area is being limited, and why there is no rush to put in underwater drones to take photos. 
 
 "The better the Ocean Shield can define the area the easier it will be for the Autonomous Underwater Vehicle to subsequently search for aircraft wreckage," Houston said. 
 
 Bear in mind with the Air France disaster, it took the underwater vehicle 20 days to get to the wreckage." 
 
 What happens after the Malaysian plane's pingers die? 
 
 And it's not as if, if more pulses are detected, they'll lead down in a straight line to the flight recorders. As is, the pings that were heard could have emanated from anywhere within a 5-mile radius, said Mary Schiavo, a former inspector general for the U.S. Department of Transportation. 
 
 Finding more signals could narrow the search area. Without them, authorities could then start the painstaking process of using side-scanning sonar to try to find the aircraft on the ocean's bottom. 
 
 Meanwhile, the air search continues. As McEvoy explained, this area is "slightly different" than that being probed for pings because it is focused on surface debris, which would have shifted over the past few weeks -- thanks in part to a cyclone packing winds in excess of 160 mph that pushed through two weeks ago. 
 
 So far, none of the aircraft that have been sent out has found anything. And even if it is narrowed, Wednesday's air search area is still roughly the size of South Carolina. 
 
 As Wing Cmdr. Andy Scott of New Zealand stated: "It's a large task that's still ahead of us." 
 
 Next steps in underwater search 
 
 Pings without wreckage 'befuddling' 
 
 The absence of wreckage near these detected signals leaves some skeptical, worried that the Chinese and Australian ship's finds could be yet another false lead in an investigation that's been full of them. 
 
 Acknowledging "a very high-speed vertical impact" could explain the lack of aircraft remnants, CNN aviation analyst Miles O'Brien said there's reason to be cautious. 
 
 "It's either the most extraordinary event, or those pings weren't real," O'Brien said. "It's somewhat befuddling." 
 
 Sarah Bajc, the partner of American passenger Philip Wood, isn't convinced about anything. She told CNN's Erin Burnett she thinks the plane was hijacked. Whether that proves true, one thing she won't believe are the Malaysian officials heading the investigation. 
 
 "All of us pretty well agree that until there's the bulk of the plane, the bulk of the bodies discovered, and a black box intact, we won't believe that it's final evidence," Bajc said early Wednesday from Beijing. "... I don't think the authorities have given us much confidence of their investigative skills so far." 
 
 The lack of clarity makes it hard to "grieve properly and ... move on," -- something that she's not yet willing to do. 
 
 "I want to fight to find him, in whatever form that ends up being," said Bajc, who is coordinating with other passengers' kin to press for answers. "And I think most of the families feel the same way." 
 
 Until they get answers, women and men like Steve Wang -- whose mother was on the Malaysia Airlines plane -- are clinging to hope while trying to hold themselves together. 
 
 "We're just going through so many kinds of emotion," said Wang. "... Desperate, sad and helpless -- something like that. Everything." 
 
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– Australian officials have sounded a fresh note of confidence in the search for Malaysia Airlines Flight 370, saying they've reacquired underwater signals following a lapse into silence. Search chief Angus Houston says an Australian navy vessel detected two sets of pings yesterday in the same area that signals were detected over the weekend, reports the Sydney Morning Herald. "I'm now optimistic that we will find the aircraft, or what is left of the aircraft, in the not too distant future—but we haven't found it yet, because this is a very challenging business," Houston told reporters. The signals are getting weaker, which could be a sign that searchers are getting further away, or, more likely, a sign that the data recorder batteries are starting to fade, explained Houston. He says they have delayed deploying the autonomous underwater vehicle Bluefin-21 to search for wreckage because with time running out, they don't want anything to get in the way of the signals. In another promising development, authorities have analyzed the pings detected over the weekend and confirmed that they came from electronic equipment, with signals consistent with those of flight data recorders, CNN reports.