The search for Malaysia Airlines flight MH370 has entered its fourth week, with the plane believed to have crashed in the southern Indian Ocean, thousands of miles from its original flight path.
Just as the batteries on the locator beacons on the aircraft's "black boxes" are nearing their limits, the searchers have detected signals they believe are "consistent" with the flight recorders.
Australian authorities said the signals may represent the best lead yet after the international investigation into the ill-fated carrier was initially stymied by several false leads.
Many questions about the fate of MH370, which left Kuala Lumpur en route to Beiing on March 8 with 239 passengers and crew, remain unanswered, including why the flight diverted from its planned route and what exactly caused it to crash.
The lack of information has taken a toll on the families of those on board the flight who until the announcement had been clinging on to hope their relatives may still be alive.
Here is a chronology of the latest developments:
Signals picked up by a black-box detector attached to an Australian ship were consistent with aircraft flight recorders, Australian officials said.
Two signals have been detected off the northwest coast of Australia, with the first held for 2.5 hours before contact was lost and the second for around 13 minutes. Confirmation of whether the signals are related to the missing flight could take several days, said Angus Houston, who is heading the Australian agency coordinating the search.
While the signals are about 300 nautical miles away from the location where a Chinese patrol ship detected a signal earlier in the week, but authorities noted that sound can travel great distances in deep water.
A Chinese patrol ship detected a pulse signal in the south Indian Ocean, according to a report from state-owned news agency Xinhua. Both Xinhua and Australian search authorities said the signal was "consistent" with a black box, but noted there was no conclusive evidence linking the signal to Flight MH370.
Malaysia released the full transcript of communications between MH370 and air traffic control before the flight dropped off of civilian radar. The last words were "good night, Malaysian three seven zero," Malaysian authorities said. Previously, authorities had said the last communication was "all right, good night."
"There is no indication of anything abnormal in the transcript," Hishammuddin Hussein, Malaysia's acting transport minister, said.
The search area was shifted closer to Australia after further analysis of satellite data suggested the plan may have been traveling faster than earlier estimates, possibly running out of fuel sooner than previously believed.
Chinese relatives of passengers stage a protest in Kuala Lumpur to demand the Malaysian government apologize for its handling of the search and for the prime minister's statement claiming the flight ended in the Indian Ocean.
Tuesday, March 25
Search suspended: Search operation for wreckage of the flight is temporarily suspended due to poor weather conditions in the southern Indian Ocean.
Monday, March 24
Confirmation of flight's fate:Malaysian Prime Minister Najib Razak says fresh analysis of satellite data tracking MH370 shows the flight went down with passengers and crew members in the southern Indian Ocean, west of Perth - a remote location, far from any possible landing sites.
Informing relatives: Malaysia Airlines sends text messages to families saying it has to be assumed that that none of those on board MH370 survived. The airline says arrangements will be made to take relatives of passengers to the recovery area once it receives approval from the investigating authorities.
More debris spotted: Earlier in the day, a Chinese plane spotted two white, square-shaped objects in an area identified by satellite imagery as containing possible debris from the missing airline.
Sunday, March 23
Search continues: An international force resumes its search efforts, zeroing in on two areas some 2,500 km southwest of Perth in an effort to find an object identified by China and other small debris including a wooden pallet spotted by a search plane on Saturday.
Debris sighting: French satellite images show possible debris from the missing jet deep in the southern Indian Ocean, Malaysian authorities said. The statement gives no details as to whether the objects were in the same vicinity as the other possible finds.
(Read more: Hope of breakthrough in missing jet search)
Hope of resolution: Australian Prime Minister Tony Abbott says there is "increasing hope" of a breakthrough in the hunt for the missing airliner.
Saturday, March 22
Satellite captures possible wreckage:China releases a new satellite image of what could be wreckage from a missing Malaysian airliner.
The satellite took an image of an object 22 meters by 13 meters. The image location was about 120 kilometers south of where an Australian satellite viewed two objects two days earlier.
The wing of a Boeing 777-200ER is approximately 27 meters long and 14 meters wide at its base, according to estimates derived from publicly available scale drawings.
Floating objects sighted: AMSA says a wooden pallet has been spotted by a search aircraft, and that it was surrounded by several other objects, including what appeared to be strapping belts of different colors.
Friday, March 21
Search efforts bear no fruit:International search efforts in the remote southern Indian Ocean fail to turn up anything and Australia's Deputy Prime Minister Warren Truss says suspected debris may have sunk. Aircraft and ships renew a search in the Andaman Sea between India and Thailand, going over areas that have already been exhaustively swept.
Thursday, March 20
Australian satellite spots debris: Australian Prime Minister Tony Abbott says satellite imagery has found two objects possibly related to the search for the plane.
Four aircraft are on route to the site to investigate the objects that are located approximately 2500 km Southwest of Perth. The largest piece of debris is 24 meters, according to satellite images.
Water in the search area is "several thousand meters deep" and poor visibility in the area could hamper the search, the Australian Maritime Safety Authority (AMSA) said.
Wednesday, March 19
FBI assisting investigation: U.S. Attorney General Eric Holder announced the FBI will be assisting the Malaysian government with the investigation, according to the Associated Press.
Malaysia discounts Maldives sighting: Investigators probing the disappearance of a Malaysia Airlines jetliner with 239 people on board have discounted reports the plane may have been sighted over the Maldives, Malaysia's Acting Transport Minister Hishammuddin Hussein said.
Several residents of Kudahuvadhoo, one of the more remote a tolls in the Indian Ocean island chain nation, had reported seeing a low-flying aircraft on the morning of March 8, when Flight MH370 disappeared enroute from Kuala Lumpur to Beijing.
Files were deleted from flight simulator: The Associated Press reported that investigators are trying to restore files deleted last month from the home flight simulator of the pilot aboard the missing Malaysian plane to see if they shed any light on the disappearance, Malaysia's defense minister said Wednesday. Files containing records of the simulations carried out on the program were deleted on Feb. 3, Malaysian police chief Khalid Abu told the news conference.
First insurance payments made for missing plane: German insurance company Allianz said it has made initial payments in connection with the missing Malaysian Airlines plane, according to The Associated Press. Allianz's global head of communication Hugo Kidston confirmed Wednesday that the Munich-based insurer and "other co-reinsurers of Malaysia Airlines aviation hull and liability policy have made initial payments."
Jet said to be most likely in southern Indian Ocean: Investigators probing the disappearance of a Malaysia Airlines jetliner with 239 people on board believe it most likely flew into the southern Indian Ocean, a source close to the investigation told Reuters.
"The working assumption is that it went south, and furthermore that it went to the southern end of that corridor," said the source, who spoke on condition of anonymity.
Missing jet's U-turn programmed before signoff: The missing Malaysia Airlines jet's abrupt U-turn was programmed into the on-board computer well before the co-pilot calmly signed off with air traffic controllers, sources told NBC News.The change in direction was made at least 12 minutes before co-pilot Fariq Abdul Hamid said "All right, good night," to controllers on the ground, the sources said.
The revelation further indicates that the aircraft's mysterious turnaround was planned and executed in the cockpit before controllers lost contact with Flight 370, but it doesn't necessarily indicate an ulterior motive.
Tuesday, March 18
China finds no terror link to its nationals: The Associated Press reported that checks into the background of the Chinese citizens on board the missing Malaysia Airlines jetliner have uncovered no links to terrorism, the Chinese ambassador in Kuala Lumpur said Tuesday.
The remarks will dampen speculation that Uighur Muslim separatists in far-western Xinjiang province might have been involved with the disappearance of the Boeing 777 and its 239 passengers and crew early on March 8.
Thai radar may have spotted missing plane: A spokesman for Thailand's air force said it may have detected Malaysia Airlines Flight 370 with radar minutes after the missing jetliner's communications went down, The Associated Press reported.
The radar tracked a plane that was flying toward to the Strait of Malacca, which is where Malaysian radar also tracked Flight 370 early March 8. The spokesman said the air force didn't share the information earlier because it wasn't specifically asked for it.
Change in flight path entered via cockpit computer: New information suggests the change in the flight's direction was plugged into a computer in the cockpit by someone familiar with airplane computer systems. The fact that the turn was programmed into the computer in the cockpit raised more questions about the possible involvement of one of the flight crew.
Monday, March 17
New phase of search underway: Search and rescue missions in the northern and southern corridors begin. Australia and Indonesia lead search in their own regions. A total of 26 countries are involved in the search.
Sunday, March 16
Search party expanded: The number of countries involved in the ongoing search for flight MH370 has expanded to 25 from 14, the Malaysian Transport Minister said at a press conference on Sunday, noting the search has entered a new phase and become more difficult.
Additional countries involved in the search effort include Kazakhstan, Uzbekistan, Kyrgyzstan, Turkmenistan, Pakistan and Bangladesh.
Corridors remain in focus: The search area remains focused on the northern and southern corridors identified earlier this weekend. Officials are currently discussing with all partners how best to deploy assets along the two corridors, both of which are being treated with equal importance.
Further investigating crew and passengers: All crew members and passengers on board flight MH370, as well as engineers who may have had contact with the aircraft prior to take off are being investigated, the Malaysian police chief said. He noted that hijacking, sabotage, personal and psychological problems remain the four areas of focus on this front.
According to the authorities, police searched the homes of both the pilot and co-pilot on Saturday, March 15. Experts are examining the flight simulator found in the pilot's house, they said.
Authorities also confirmed that the pilot and co-pilot did not request to fly together.
Saturday, March 15
"Deliberate" action taken on board: Malaysian Prime Minister Najib Razak reveals at a press conference that actions taken on board Flight MH370 were deliberate – including the disabling of the aircraft's communications system shortly before the plane reached the east coast of Malaysia as well as the flight's divergence from its planned route.
Turn back confirmed: Najib confirms that the plane turned back from its planned flight path over the over the Gulf of Thailand and the South China Sea, flying in a westerly direction back over the Malaysian Peninsula before turning northwest.
Last signal: The last confirmed signal between the plane and a satellite came at 8:11 a.m. Malaysian time — about 7 1/2 hours after takeoff.
New focus for search: Analysis of the plane's last communication with satellites places the aircraft in one of two "corridors" – a northern one from northern Thailand through to the border of Kazakhstan and Turkmenistan, and a southern one from Indonesia to the southern Indian Ocean, Najib said. Search efforts in the South China Sea are scheduled to end.
Friday, March 14
A new Indian Ocean search area possible: The White House said late Thursday that the latest expansion of the search area may be in the Indian Ocean. Several "pings" from the aircraft were picked up by satellites for up to four hours after going off radar, according to a NBC News report citing sources. The pings would indicate the plane was able to communicate. But the data would be unlikely to include exact location or direction.
The U.S. destroyer, USS Kidd, was headed into the Strait of Malacca from areas around the Gulf of Thailand, at the request of the Malaysian government, as part of the expanded search area.
Thursday, March 13
Malaysia denies Wall Street Journal report: Malaysian Transport Minister Seri Hishammuddin dismissed claims that the missing aircraft may have flown for about four hours past the time it disappeared off tracking systems. The Wall Street Journal had reported that the plane could have flown on for an additional distance of about 2,200 miles (3,500 km). Hishammuddin said their search efforts have always been focused on the South China Sea.
No link in satellite images: China's civil aviation chief said there was no proof that floating objects in the South China Sea captured in satellite images on Sunday were connected to the missing Malaysia Airlines plane. Chinese authorities also said that the satellite images had been mistakenly issued.
Wednesday, March 12
Search efforts intensify: The area of search for the missing aircraft expands to 27,000 nautical square miles covering the South China Sea and Strait of Malacca, with a total of 12 countries participating in the operation. There are a total of 42 ships and 39 aircraft currently involved in the multi-national search.
Search scale-back in Vietnamese area: Vietnam says it is scaling back its search in Vietnamese waters for the missing plane, Reuters reported.
Sighting of objects in South China Sea: A Chinese government agency releases satellite images of what could be debris from Flight MH370 were released by a Chinese government agency.
Tuesday, March 11
Clarity on stolen passports: Interpol identifies two Iranian men as the passengers traveling on stolen passports: Pouria Nourmohammadi, 18, and Seyed Mohammed Reza Delavar, 29. The two men swapped their passports in Kuala Lumpur, using stolen Italian and Austrian passports to board the airline.
Interpol says it does not believe the disappearance of the jetliner is a result of a terrorist attack. Nourmohammadi is believed to have been traveling to Europe as an asylum seeker, according to the Malaysian police.
However, Central Intelligence Agency (CIA) director John Brennan says intelligence officials cannot rule out terrorism as a factor.
'Turned back' possibility probed: Malaysia's military look further into the possibility that the airplane turned back after flying over Kota Bharu on Malaysia's northeast coast, an official from the Malaysia's Transport Ministry told NBC News.
Police investigation: The Malaysian police say their investigation will look into four key areas: hijacking, sabotage, psychological and personal problems among crew and passengers.
Allegations against first officer: Photos and videos emerge of a Malaysia Airlines co-pilot identified as first officer Fariq Ab Hamid entertaining woman inside the cockpit during a previous flight. The airline says it is "shocked" by the allegations and has not been able to confirm validity of the claims.
Monday, March 10
Oil slick results: Malaysian authorities receive test results from the oil slick spotted off Vietnam's coast, which came back negative for jet fuel. The oil turns out to be fuel oil typically used in cargo ships.
Search area widened: Malaysia's civil aviation announces that the search area will double to 100 nautical miles to cover a larger area of the Gulf of Thailand between Malaysia and Vietnam. This came after several leads from the original 50 mile-radius search parameter proved erroneous.
Shares tumble: Shares of Malaysia Airlines plummeted 18 percent to a record low in intraday trade but pared losses by the end of session to finish down 4 percent.
Sunday, March 9
'Turn back' claims: Radar tracking the flight suggests it may have "turned back" from its scheduled route to Beijing before vanishing.
Search area widened: Search radius widens to 50 nautical miles from 20 nautical miles of the last-known position of the plane, including the Strait of Malacca. More countries join the search and rescue operation including China, U.S., Singapore and the Philippines.
Stolen passports: Interpol confirms two passengers had used stolen passports and said it was checking whether others aboard had used false identity documents.
Saturday, March 8
Flight takes off: Malaysia Airlines flight MH370 departs at 12:41 a.m.local time on Saturday, and is due to land in Beijing at 6:30 a.m. on the same day. The flight was carrying 227 passengers and 12 crew members. The passengers are of at least 12 different nationalities; all crew on-board are Malaysians.
Mysterious disappearance: The flight loses contact with air traffic controllers about an hour after taking off. The last-known position of the plane was 120 nautical miles off the east coast of the Malaysian town of Kota Bharu, Malaysia Airlines chief executive Ahmad Jauhari Yahya said. The aircraft was flying in good weather conditions and disappeared without warning or a distress signal.
Search efforts begin: Malaysia and Vietnam mount a joint search and rescue mission for the missing flight.
—By CNBC.com with wires