Telecommunications experts say the odds that passengers' cellphone data can help locate the missing Malaysian jetliner are next to zero.

Locating the mobile phones of the 239 travelers on the Boeing 777 that vanished Saturday isn't as simple as activating a "Find My iPhone" app, given the speed the plane was traveling, its altitude and the fact it was probably flying over water. Many people assume smartphones to be all-powerful tracking devices. Often police, rescue units and others can use a person's phone to pinpoint the user's precise location. Even so, there are large portions of the planet that don't have the transmission towers that are necessary for mobile communications. In the case of Malaysian Airlines Flight 370, smartphones are unlikely to lead investigators to the plane.

Here's what you need to know about mobile connections and how they're used to determine location:

Q: Can telecommunications providers remotely locate a phone?

A: Yes, if the phone is tuned on and is connected to either a cellular or Wi-Fi network, says Ritch Blasi, senior vice president for mobile and wireless at the consulting firm Comunicano. Apps like "Find My iPhone" only function properly when a phone is able to receive a location signal from a GPS satellite and relay that signal via cell connection or Wi-Fi to those who are searching for it.

Q: Does this change when you're on a plane?

A: Yes, considerably. For one thing, most airlines require passengers to turn their phones off or at least put them in airplane mode before takeoff. That means there's no connection to a cellular network, says Blasi. Even if some passengers left their phones on during Flight 370, it would be tough for their phones to connect with a tower given the speeds planes travel at and the altitudes involved.

Q: What about flying over the ocean?

A: Flying over oceans reduces the odds of a connection even more, since there just aren't cell towers there. Charles McColgan, chief technology officer for the mobile identity firm TeleSign says that while investigators might be able to determine the last cell tower that cellphones had contact with before the plane started flying over water, if the plane was flying above 10,000 feet at the time, the phones on it wouldn't be able to make a connection with a tower.

"Anyone leading the investigation should check, but it is unlikely that pinging a passenger's phone is going to find them," McColgan says.

Q: What if the plane managed to crash on land and some people and phones survived?

A: If someone could get a signal, in theory they could make a call. But if the plane went down in a remote area without service, then they would be out of luck. Foreign travel also complicates things. Unless a person signs up for local phone service in whatever country they're traveling through, his or her phone may not be able to connect to a network, says Blasi, who spent more than 35 years at AT&T before going into consulting.

Q: What about reports of people who claim they called the phones of loved ones who were on the flight and said the phone rang several times without an answer, rather than going straight to voice mail, indicating that the phone might be connected to a network?

A: This doesn't necessarily mean that the phone is connected to a network, is turned on, or is even operational. It just means that the cellular carrier's system is taking some time to look for the phone.

Q: Is there any hope if the plane crashed in the water and the phones on board were soaked?

A: Water and electronics don't mix, so generally speaking the answer is no.