Story highlights Officials say a new signal may have been detected Thursday

The search area has been narrowed to 22,400 square miles

The pings are coming from the ocean floor 15,000 feet below surface

That's deeper than an inverted Eiffel Tower or the Burj Khalifa

Just how hard is it to find a plane at the bottom of the ocean?

Imagine standing on a mountain top and trying to spot a suitcase on the ground below. Then imagine doing it in complete darkness.

That's basically what crews searching for Malaysia Airlines Flight 370 have been trying to do for a month.

Thursday is Day 34 in the search for the plane that disappeared March 8, taking with it 239 passengers and crew members.

Photos: The search for MH370 Photos: The search for MH370 Two years after Malaysia Airlines Flight 370 went missing, a relative of one of the passengers burns incense in Beijing on March 8, 2016. Flight 370 vanished on March 8, 2014, as it flew from Kuala Lumpur, Malaysia, to Beijing. There were 239 people on board. Hide Caption 1 of 43 Photos: The search for MH370 On July 29, police carry a piece of debris on Reunion Island, a French territory in the Indian Ocean. A week later, authorities confirmed that the debris was from the missing flight. Hide Caption 2 of 43 Photos: The search for MH370 Staff members with the Australian Transport Safety Bureau examine a piece of aircraft debris at their laboratory in Canberra, Australia, on July 20. The flap was found in June by residents on Pemba Island off the coast of Tanzania, and officials had said it was highly likely to have come from Flight 370. Experts at the Australian Transport Safety Bureau, which is heading up the search for the plane, confirmed that the part was indeed from the missing aircraft. Hide Caption 3 of 43 Photos: The search for MH370 In late February, American tourist Blaine Gibson found a piece of plane debris off Mozambique, a discovery that renewed hope of solving the mystery of the missing flight. The piece measured 35 inches by 22 inches. A U.S. official said it was likely the wreckage came from a Boeing 777, which MH370 was. Hide Caption 4 of 43 Photos: The search for MH370 Relatives of the flight's passengers console each other outside the Malaysia Airlines office in Subang, Malaysia, on February 12, 2015. Protesters had demanded that the airline withdraw the statement that all 239 people aboard the plane were dead. Hide Caption 5 of 43 Photos: The search for MH370 A police officer watches a couple cry outside the airline's office building in Beijing after officials refused to meet with them on June 11, 2014. The couple's son was on the plane. Hide Caption 6 of 43 Photos: The search for MH370 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 May 27, 2014. Data from communications between satellites and the missing flight was released the day before, more than two months after relatives of passengers said they requested it be made public. Hide Caption 7 of 43 Photos: The search for MH370 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 April 14, 2014. Hide Caption 8 of 43 Photos: The search for MH370 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 April 13, 2014. Hide Caption 9 of 43 Photos: The search for MH370 The HMS Echo, a vessel with the British Roya; Navy, moves through the waters of the southern Indian Ocean on April 12, 2014. Hide Caption 10 of 43 Photos: The search for MH370 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, 2014. Hide Caption 11 of 43 Photos: The search for MH370 A relative of a missing passenger cries at a vigil in Beijing on April 8, 2014. Hide Caption 12 of 43 Photos: The search for MH370 Australian Defense Force divers scan the water for debris in the southern Indian Ocean on April 7, 2014. Hide Caption 13 of 43 Photos: The search for MH370 A towed pinger locator is readied to be deployed off the deck of the Australian vessel Ocean Shield on April 7, 2014. Hide Caption 14 of 43 Photos: The search for MH370 A member of the Royal New Zealand Air Force looks at a flare in the Indian Ocean during search operations on April 4, 2014. Hide Caption 15 of 43 Photos: The search for MH370 On March 30, 2014, a woman in Kuala Lumpur prepares for an event in honor of those aboard Flight 370. Hide Caption 16 of 43 Photos: The search for MH370 The sole representative for the families of Flight 370 passengers leaves a conference at a Beijing hotel on March 28, 2014, after other relatives left en masse to protest the Malaysian government's response to their questions. Hide Caption 17 of 43 Photos: The search for MH370 A member of the Royal Australian Air Force is silhouetted against the southern Indian Ocean during the search for the missing jet on March 27, 2014. Hide Caption 18 of 43 Photos: The search for MH370 Flight Lt. Jayson Nichols looks at a map aboard a Royal Australian Air Force aircraft during a search on March 27, 2014. Hide Caption 19 of 43 Photos: The search for MH370 People in Kuala Lumpur light candles during a ceremony held for the missing flight's passengers on March 27, 2014. Hide Caption 20 of 43 Photos: The search for MH370 Malaysian Prime Minister Najib Razak, center, delivers a statement about the flight on March 24, 2014. 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 21 of 43 Photos: The search for MH370 Grieving relatives of missing passengers leave a hotel in Beijing on March 24, 2014. Hide Caption 22 of 43 Photos: The search for MH370 A passenger views a weather map in the departures terminal of Kuala Lumpur International Airport on March 22, 2014. Hide Caption 23 of 43 Photos: The search for MH370 A Chinese satellite captured this image, released on March 22, 2014, of a floating object in the Indian Ocean, according to China's State Administration of Science. It was a possible lead in the search for the missing plane. Surveillance planes were 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 24 of 43 Photos: The search for MH370 Satellite imagery provided by the Australian Maritime Safety Authority on March 20, 2014, showed debris in the southern Indian Ocean that could have been from Flight 370. The announcement by Australian officials raised hopes of a breakthrough in the frustrating search. Hide Caption 25 of 43 Photos: The search for MH370 Another satellite shot provided by the Australian Maritime Safety Authority shows possible debris from the flight. Hide Caption 26 of 43 Photos: The search for MH370 A distraught relative of a missing passenger breaks down while talking to reporters at Kuala Lumpur International Airport on March 19, 2014. Hide Caption 27 of 43 Photos: The search for MH370 On March 18, 2014, 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 28 of 43 Photos: The search for MH370 U.S. Navy crew members assist in search-and-rescue operations in the Indian Ocean on March 16, 2014. Hide Caption 29 of 43 Photos: The search for MH370 Members of the Chinese navy continue search operations on March 13, 2014. After starting in the sea between Malaysia and Vietnam, the plane's last confirmed location, search efforts expanded west into the Indian Ocean. Hide Caption 30 of 43 Photos: The search for MH370 A Vietnamese military official looks out an aircraft window during search operations March 13, 2014. Hide Caption 31 of 43 Photos: The search for MH370 Malaysian air force members look for debris near Kuala Lumpur on March 13, 2014. Hide Caption 32 of 43 Photos: The search for MH370 Relatives of missing passengers wait for the latest news at a hotel in Beijing on March 12, 2014. Hide Caption 33 of 43 Photos: The search for MH370 A member of the Vietnamese air force checks a map while searching for the missing plane on March 11, 2014. Hide Caption 34 of 43 Photos: The search for MH370 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 on March 8, 2014. 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, 2014. Hide Caption 35 of 43 Photos: The search for MH370 A U.S. Navy Seahawk helicopter lands aboard the USS Pinckney to change crews on March 9, 2014, before returning to search for the missing plane in the Gulf of Thailand. Hide Caption 36 of 43 Photos: The search for MH370 Buddhist monks at Kuala Lumpur International Airport offer a special prayer for the missing passengers on March 9, 2014. Hide Caption 37 of 43 Photos: The search for MH370 Members of a Chinese emergency response team board a rescue vessel at the port of Sanya in China's Hainan province on March 9, 2014. Hide Caption 38 of 43 Photos: The search for MH370 The rescue vessel sets out from Sanya in the South China Sea on March 9, 2014. Hide Caption 39 of 43 Photos: The search for MH370 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, 2014. Hide Caption 40 of 43 Photos: The search for MH370 A relative of two missing passengers reacts at their home in Kuala Lumpur on March 8, 2014. Hide Caption 41 of 43 Photos: The search for MH370 Chinese police at the Beijing airport stand beside the arrival board showing delayed Flight 370 in red on March 8, 2014. Hide Caption 42 of 43 Photos: The search for MH370 Malaysia Airlines Group CEO Ahmad Juahari Yahya, front, speaks during a news conference at a hotel in Sepang on March 8, 2014. "We deeply regret that we have lost all contacts" with the jet, he said. Hide Caption 43 of 43

JUST WATCHED Searching the depths of the Indian Ocean Replay More Videos ... MUST WATCH Searching the depths of the Indian Ocean 02:02

JUST WATCHED CNN joins MH370 search over Indian Ocean Replay More Videos ... MUST WATCH CNN joins MH370 search over Indian Ocean 02:45

JUST WATCHED Could the pings be from MH370? Replay More Videos ... MUST WATCH Could the pings be from MH370? 02:07

Officials believe the Boeing 777, while en route from Kuala Lumpur, Malaysia, to Beijing, crashed in the southern Indian Ocean.

Pinning their hopes on signals they think came from the plane's black boxes, they narrowed the focus of their search Thursday to a 22,400-square-mile (58,000-square-kilometer) area -- about 45 times the size of Los Angeles.

But the real challenge is the depth of the water they're dealing with.

Staggering depths

The underwater pulses that were detected Saturday, and again Tuesday, came from the ocean floor 15,000 feet below the surface. That's 2.8 miles (4.5 kilometers). On Thursday, officials said another signal may have been detected from sonar buoys.

How deep is 2.8 miles? It's deeper than an inverted Statue of Liberty (305 feet), deeper than an inverted Eiffel Tower (1,063 feet), deeper even than an inverted Burj Khalifa, the tallest building in the world (2,717 feet).

In fact, if you stacked the Burj end-to-end five times, it would reach only 14,000 feet -- still not deep enough to reach the spot searchers believe the pings are coming from.

At these depths, marine life is unlike anything most people have ever seen.

"The deeper you go you find less and less," marine biologist Paula Carlson said. "They have to be very cold tolerant, they might not even have eyes. They may be blind, because they don't need to see, there's no light down there."

Keep plunging

The pressure at nearly 15,000 feet is crushing -- so much so that very few manned submarines can withstand it.

"There are only about half a dozen subs that can go to half the ocean depth with a number of countries having that capability," said Sylvia Earle, an oceanographer for National Geographic. "If it gets to the point of collapse, it basically implodes, it just crushes."

Only a handful of people have traveled to such staggering depths. One of them is movie director James Cameron, who using a state-of-the-art vessel, dropped 35,000 feet, or about 7 miles , to the deepest place on Earth -- the Challenger Deep in the western Pacific Ocean.

A daunting task

Finding the plane is daunting. Bringing it back from the deep will be even more difficult.

JUST WATCHED What you need to know about a black box Replay More Videos ... MUST WATCH What you need to know about a black box 01:51

JUST WATCHED Up to 14 planes in search for Flight 370 Replay More Videos ... MUST WATCH Up to 14 planes in search for Flight 370 02:42

JUST WATCHED Hiding in another plane's shadow? Replay More Videos ... MUST WATCH Hiding in another plane's shadow? 03:57

"At these depths ... there's no recovery like it," said Mary Schiavo, a former inspector general for the U.S. Department of Transportation.

When the Titanic struck an iceberg and sank in the Atlantic, it took some 70 years to discover the wreckage. It was resting 12,500 feet below the ocean's surface, and it still lies there today.

When Air France Flight 447, with 228 people on board, plunged into the South Atlantic Ocean during a storm in 2009, the precise location of the wreckage remained a mystery for almost two years.

Then the plane and its dead were found in a mountain range 13,100-feet deep on the ocean floor. Miniature submersible vehicles retrieved the Flight 447's voice and flight data recorders.

Eventually 154 bodies were recovered. Seventy-four still rest in the watery grave.

Not giving up

But Amirtham Arupilai isn't accepting that fate for her son, Puspanathan, who was on board MH370.

"My inside and my heart is telling me still they are alive -- all the passengers are alive," Arupilai said.

Her son, an IT specialist, was headed to Beijing to begin a new job. To his parents, he was everything.

She calls Puspanathan's cell phone and hears his voice mail greeting. She takes it as a sign he must be safe.