Crews narrowed search area

• Thursday is Day 34 of the search


• 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

(CNN) -- 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.

Searching the depths of the Indian Ocean

Could the pings be from MH370?

Hear possible 'ping' detected in search

A Royal Australian Air Force AP-3C Orion flies past the Australian vessel Ocean Shield on Wednesday, April 9, on a mission to drop sonar buoys to assist in the search for the missing Malaysia Airlines Flight 370 in the southern Indian Ocean. Searchers are combing thousands of square miles of the ocean for signs of Flight 370, which disappeared March 8.

A relative of a passenger on the missing flight cries at a vigil in Beijing on Tuesday, April 8.

A member of the Royal Australian Air Force walks toward a plane that has just arrived in Perth, Australia, on April 8.

Australian Defense Force divers from the Ocean Shield vessel scan the water for debris in the southern Indian Ocean on Monday, April 7.

A towed pinger locator is readied to be deployed on April 7 off the deck of the Australian vessel Ocean Shield in the search for the missing jet's flight data recorder and cockpit voice recorder.

Capt. Mark Matthews of the U.S. Navy talks to reporters in Perth on April 7 about the search.

A member of the search operation points to a map outlining the current search areas during a press conference on April 7 in Perth.

A U.S. Navy airplane takes off from Perth to assist in the search on April 7.

A member of the Royal New Zealand Air Force looks at a flare in the Indian Ocean on Friday, April 4, during search operations.

Members of the Royal New Zealand Air Force monitor data April 4 on board an aircraft during search operations.

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.

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.

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.

Kojiro Tanaka, head of the Japanese coast guard search mission, explains the efforts en route to the search zone April 1.

A woman prepares for an event in honor of those aboard Flight 370 on Sunday, March 30, in Kuala Lumpur, Malaysia.

An underwater search-surveying vehicle sits on the wharf in Perth, Australia, ready to be fitted to a ship to aid in the search for the jet.

A girl in Kuala Lumpur writes a note during a ceremony for the missing passengers on March 30.

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.

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.

A Royal New Zealand Air Force member launches a GPS marker buoy over the southern Indian Ocean on March 29.

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.

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.

Flight Lt. Jayson Nichols looks at a map aboard a Royal Australian Air Force aircraft during a search on March 27.

People in Kuala Lumpur light candles during a ceremony held for the missing flight's passengers on March 27.

Crew members of the Chinese icebreaking ship Xuelong scan the Indian Ocean during a search for the missing jet on Wednesday, March 26.

People work at a console at the British satellite company Inmarsat on Tuesday, March 25, in London.

The mother of a passenger who was on Malaysia Airlines Flight 370 cries at her home in Medan, Indonesia, on March 25.

Australian Defense Minister David Johnston speaks to the media March 25 about the search for the missing jet.

A family member of a missing passenger reacts after hearing the latest news March 25 in Kuala Lumpur.

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.

Grieving relatives of missing passengers leave a hotel in Beijing on March 24.

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."

Relatives of the missing passengers hold a candlelight vigil in Beijing on March 24.

A member of the Royal Australian Air Force looks out an aircraft during a search for the missing jet March 24.

A woman reads messages for missing passengers at a shopping mall in Kuala Lumpur on March 24.

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.

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.

A passenger views a weather map in the departures terminal of Kuala Lumpur International Airport on Saturday, March 22.

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.

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.

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.

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.

A closer look at the satellite shot of possible debris from Malaysia Airlines Flight 370.

Another satellite shot provided by the Australian Maritime Safety Authority shows possible debris from the flight.

A closer look at the satellite shot of possible debris.

The Australian Maritime Safety Authority's John Young speaks to the media in Canberra, Australia, on March 20 about satellite imagery.

A distraught relative of a missing passenger breaks down while talking to reporters at Kuala Lumpur International Airport on Wednesday, March 19.

A relative of missing passengers waits for a news briefing by officials in Beijing on Tuesday, March 18.

A relative of a missing passenger tells reporters in Beijing about a hunger strike to protest authorities' handling of information about the missing jet.

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.

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.

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.

U.S. Navy crew members assist in search-and-rescue operations Sunday, March 16, in the Indian Ocean.

Indonesian personnel watch over high seas during a search operation in the Andaman Sea on Saturday, March 15.

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.

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.

A Indonesian ship heads to the Andaman Sea during a search operation near the tip of Sumatra, Indonesia, on March 15.

Elementary school students pray for the missing passengers during class in Medan, Indonesia, on March 15.

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.

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.

A Vietnamese military official looks out an aircraft window during search operations March 13.

Malaysian air force members look for debris on March 13 near Kuala Lumpur.

A relative of a missing passenger watches TV at a Beijing hotel as she waits for the latest news March 13.

A member of the Indonesian National Search and Rescue Agency scans the horizon in the Strait of Malacca on Wednesday, March 12.

Relatives of missing passengers wait for the latest news at a hotel in Beijing on March 12.

Journalists raise their hands to ask questions during a news conference in Sepang on March 12.

Indonesian air force officers in Medan, Indonesia, examine a map of the Strait of Malacca on March 12.

A member of the Vietnamese air force checks a map while searching for the missing plane on Tuesday, March 11.

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.

An Indonesian navy crew member scans an area of the South China Sea bordering Indonesia, Malaysia and Thailand on Monday, March 10.

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.

Relatives of the missing flight's passengers wait in a Beijing hotel room on March 10.

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.

Members of the Fo Guang Shan rescue team offer a special prayer March 9 at Kuala Lumpur International Airport.

A handout picture provided by the Malaysian Maritime Enforcement Agency shows personnel checking a radar screen during search-and-rescue operations March 9.

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.

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.

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.

Buddhist monks at Kuala Lumpur International Airport offer a special prayer for the missing passengers on March 9.

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.

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.

The rescue vessel sets out from Sanya in the South China Sea.

A family member of missing passengers is mobbed by journalists at Kuala Lumpur International Airport on Saturday, March 8.

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.

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.

Malaysia Airlines official Joshua Law Kok Hwa, center, speaks to reporters in Beijing on March 8.

A relative of two missing passengers reacts at their home in Kuala Lumpur on March 8.

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.

Chinese police at the Beijing airport stand beside the arrival board showing delayed Flight 370 in red on March 8.

A woman asks a staff member at the Beijing airport for more information on the missing flight.

A Malaysian man who says he has relatives on board the missing plane talks to journalists at the Beijing airport on March 8.

Passengers walk past a Malaysia Airlines sign on March 8 at Kuala Lumpur International Airport.

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.

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

The search for Malaysia Airlines Flight 370

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

Photos: The search for Malaysia Airlines Flight 370

What you need to know about a black box

Up to 14 planes in search for Flight 370

Hiding in another plane's shadow?

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

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 signals 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).

That'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.

"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.

Four reasons to believe; six reasons to doubt

More pings raise more questions

What happens after the Malaysian plane's pingers die?

Next steps in underwater search

Timeline: Leads in the hunt for Flight 370 weave drama