Why are missing Malaysia Airlines passengers' phones still ringing?

Family members of passengers missing on Malaysian Airlines flight 370 had a brush with hope in the past few days: their missing loved ones’ mobile phones still ring.

Though flight 370 mysteriously vanished over the Gulf of Thailand four days ago, the families of 19 missing passengers have signed a statement saying they have been able to call their loved ones’ phones and hear ringing, according to China.org.cn. The phone calls have all disconnected after ringing.

Does this mean that phones are still on and working? Why aren’t missing passengers picking up when their families call?

Though we won’t know the answer for sure until the plane is located, technology industry analyst Jeff Kagan says even if a phone is off, a call placed to a mobile device can still ring.

“When you place a call it takes a few moments for the call to be completed, so phone companies typically start the ringing tone so you know it is ringing,” he says. “[That way] you know it is being connected so you won’t hang up and try again.”

There are several steps to the connection process, he says. When you make a call to a mobile device, the carrier finds the closest cell tower to where the recipient of the call last was registered. If the recipient isn’t in the range of that tower, it continues expanding out to larger areas to try to find the network the recipient is on. If it can’t find the recipient, the call disconnects, goes to voice mail, or gives an error message. Phone calls can end up disconnected because the network is over capacity or if a caller has repeatedly called too many times, he says.

“Basically the carrier is placing you on hold while it searches for the other phone, and the sound you hear instead of hold music is ringing,” Mr. Kagan explains.

This can even happen when a phone is destroyed, waterlogged, out of network, or entirely off, he says. The phones won’t stop ringing until the carrier terminates the phone number.

“That [could] put false hope in the minds of families who are desperately trying to reach their loved ones,” he says.

Kagan says it isn’t likely that carriers will change their ring-until-connected practice, unless disasters like this happen more often.

“This raises questions that we never even asked other times,” he says. “We sort of expect a little more courtesy. [But] these are things you never think about until a disaster.”