NEW YORK — The disappearance of Malaysia Airlines Flight 370 has presented two tales of modern technology.

The limitations of tracking and communications devices allowed the plane to vanish from sight for three weeks. But satellites’ advanced capabilities have provided hope the mystery won’t go unsolved.

In this day and age of constant connection, the public has been surprised to learn that radar and satellites aren’t actually all-seeing, cell phone locations aren’t always traceable and key data about the plane is only recorded, not transmitted in real time to the ground. And onboard tracking systems can be disabled manually.

“Technology can track a flight, but assuming malice was involved, it wouldn’t change the outcome of this disaster. Only better human intelligence and screening can do that,” said Richard Aboulafia, an aviation consultant with the Teal Group.

Still, the mystery of Flight 370 would have been even more perplexing if it wasn’t for some of these technologies. The little information we have today about where the plane might have crashed came from satellites.

“If it weren’t for the technologies, nobody would have had a clue where to look,” said Scott Hamilton, managing director of aviation consultancy Leeham Co.

Here is a look at how old and new technologies have aided or hindered the search effort.

TRANSPONDERS

These cockpit devices send signals to radar stations on the ground with details about the plane’s flight number, heading, speed and altitude. The transponder also can be used to send predetermined messages to air traffic controllers.

For instance, if a plane’s transponder squawks out a code of “7500” it means there has been a hijacking. A squawk of “7600” refers to a radio failure and “7700” means an emergency.

Flight 370 took off from Kuala Lumpur, Malaysia, at 12:40 a.m. local time on March 8, heading to Beijing. Then at 1:20 a.m., the transponder stopped transmitting. The Boeing 777-200ER with 239 passengers and crew aboard kept flying for several hours but no further signals were ever received from the transponder.

It’s rare for a commercial pilot to intentionally turn off a transponder during flight, but occasionally there is a legitimate reason, such as a malfunction, electrical short or fire. Pilots would want to shut it down rather than risk a fire spreading.

RADAR

Radar was developed just before the start of World War II. The word radar is actually an acronym: radio (use the R and the A) detection and ranging.

An antenna on the ground sends out electromagnetic waves. They reflect, or backscatter, from the surface of an aircraft and almost instantly return to the radar station. Because these radio waves travel at a known, set speed — the speed of light — the radar system is able to calculate how far away a plane is from the antenna.

But radar’s only able to track planes within 200 to 250 miles, depending on the age of the technology and the weather. Station locations are selected to allow for a slight overlap so planes in high-traffic areas are never out of reach.

In the case of the Malaysia Airlines jet, military radar picked up a signal at 2:14 a.m. of a plane flying in the opposite direction of Flight 370’s original path. The radar signal was infrequent and there was no transponder data, making it harder to track.

Normally, when planes leave areas of radar coverage, pilots use high-frequency radios or satellite text communications to update air traffic controllers of their position at routine intervals.

SATELLITE TRACKING

Some jets use satellites to regularly send maintenance data back to headquarters. Malaysia Airlines did not opt to subscribe to this service from Boeing.

The jet’s disappearance has many calling for airlines to live stream information from planes’ voice and data recorders. However, transmitting data by satellite from all 80,000 daily flights worldwide wouldn’t be cheap — it costs $7 to $13 a minute for each plane. And it’s not like airlines are flush with extra cash. On average, they made $4.13 in profit per passenger last year and $2.05 in 2012.

Other satellite transmissions from the plane, however, helped searchers ultimately narrow in on the plane’s final location in a remote part of the Indian Ocean.

The plane automatically sent a brief signal — a “ping” — every hour to a satellite belonging to Inmarsat, a British company, even after other communication systems shut down. The pings indicated the jet kept flying for seven hours after its last radar contact.