Malaysia Flight 370: The 10 big questions

READ: Malaysia Airlines Flight 370: Days pass, no word of loved ones

Here are 10 questions surrounding what we know and what we don’t know:

1. What do we know about the pilots?

The pilot, Capt. Zaharie Ahmad Shah, 53, has 18,365 flying hours. He joined the airline in 1981. For a veteran 777 pilot with Shah’s background, 18,000-plus total career hours in the air is normal.

Shah built a flight simulator in his home. It’s somewhat common among the worldwide community of aviation enthusiasts to use online flight simulator programs to replicate various situations. Simulators allow users to virtually experience scenarios in various aircraft.

Programs can simulate flight routes, landings and takeoffs from actual airports, but pilots say they cannot replace the experience gained from real flying.

Shah is married and has three children, the youngest of whom is in her 20s and lives with her parents. He and his wife have one grandchild.

First Officer Fariq Ab Hamid, 27, joined Malaysia Airlines in 2007. He has 2,763 flying hours and was transitioning from flight simulator training to the Boeing 777-200ER.

The amount of flight time Hamid has could be a bit low for a 777 pilot flying for an American airline, experts said. But the system of pilot advancement is often faster among airlines in smaller nations. Some airlines in these countries offer cadet programs that find talented and promising young pilot candidates and offer them intensive, specialized training, experts say.

Hamid lives with his parents and some of his four siblings, according to a neighbor. A source close to the investigation told CNN that Malaysian police searched Shah’s and Hamid’s homes Saturday.

Read more about the pilots

2. What do we know about communications to and from the plane?

Key clues about the plane have come from developments surrounding data and voice communications. The plane is equipped with a standard voice communication radio and two other kinds of communication technology: transponders and the Aircraft Communications Addressing and Reporting System, known by the acronym ACARS.

The last known voice communication from the 777’s cockpit was these words: “All right, good night.”

We don’t know whose voice spoke the words, but they were uttered as the plane neared Vietnamese air traffic control airspace at about the same time the transponder was shut off, according to Malaysian Prime Minister Najib Razak.

Because of the vital information a transponder provides, it would be highly unlikely for a pilot to shut it off. Transponders are considered reliable, but they occasionally fail, which is why there is a backup transponder.

One way to hide a plane’s flight information from air traffic controllers would be to turn off the transponder. Experts give conflicting opinions about what the transponder shutoff could mean: One theory points to someone – perhaps a hijacker – wanting to hide the plane before changing course; another theory is the transponder could have stopped transmitting because of a catastrophic power failure.

A series of “handshakes” – or electronic connections – from the plane’s ACARS was transmitted to satellites for four to five hours after the transponder stopped sending signals, a senior U.S. official told CNN.

ACARS includes air traffic service communications. The automated system generally sends routine messages to the airline, such as when the aircraft lifts off or lands and how much fuel it may have, he said. It can also be used to communicate text messages, for instance when the aircraft encounters turbulence. ACARS typically beams down engine parameters, temperatures, the amount of fuel burned and any maintenance discrepancies.

According to Malaysia Airlines, all of its aircraft are equipped with ACARS. “Nevertheless, there were no distress calls, and no information was relayed,” the airline said.

The aircraft’s ACARS was sending pings more than five hours after the transponder last emitted a signal, an aviation industry source told CNN on Friday.

These pings don’t provide information about speed or altitude, but they do indicate the plane was intact for that long, since an aircraft has to be powered and have structural integrity for the ACARS to operate, the source said.

The pings were detected by satellites and were used, with radar and other data, to calculate where the plane might have traveled. A U.S. official, who spoke to reporters on condition of anonymity, said a satellite recorded electronic “handshakes” with the 777 that were later analyzed.

The information gleaned from this analysis – which the U.S. official described as “unprecedented” – supports the conclusion that the aircraft turned toward the west, away from the Gulf of Thailand and toward the Indian Ocean. Referring to the five- to six-hour range in which the plane may have flown after its transponder cut off, the same official said, “We believe we have the time of the loss of the airplane within an hour.”

But on Saturday, Malaysian Prime Minister Najib said that “based on new satellite communication, we can say with a high degree of certainty that … ACARS was disabled just before the aircraft reached the east coast of peninsular Malaysia.”

Snapshots of the passengers

3. Where could the plane be? What could have happened to it?

The evidence is growing that the plane flew for hours after losing contact with air traffic control.

Malaysia