SEPANG, Malaysia — A signaling system was disabled on the missing Malaysia Airlines jet before a pilot spoke to air traffic control without mentioning trouble, a senior Malaysian official said Sunday, reinforcing theories that one of the pilots may have been involved in diverting the plane.
With the increasing likelihood that Flight 370 was purposefully diverted and flown possibly thousands of miles from its planned route, Malaysian officials faced more questions about how the investigation, marked by days of contradictory government statements, might have ballooned into a global scramble for reliable information.
Prime Minister Najib Razak acknowledged Saturday that military radar and satellite data raised the possibility that the plane could have ended up somewhere in Indonesia, the southern Indian Ocean, or along a vast arc of territory from northern Laos across western China to Central Asia.
Malaysian officials said they were scrambling to coordinate a 25-nation effort to find the plane.
And on Sunday, Malaysia’s defense minister added a critical detail about investigators’ understanding of what transpired in the cockpit in the 40 minutes of flight time before ground controllers lost contact with the jet.
The determination that the last verbal message to the control tower — “All right, good night,” someone said — came after a key signaling system had stopped transmitting, perhaps having been shut off, appeared likely to refocus scrutiny on the plane’s veteran pilot, Captain Zaharie Ahmad Shah, and his first officer, Fariq Abdul Hamid.
Commercial passenger planes use radio or satellite signals to send data through ACARS, the Aircraft Communications Addressing and Reporting System. The system can monitor equipment for problems that may need attention.
Although officials had already said that ACARS was disabled on the missing plane, it had previously been unclear whether the system stopped functioning before or after the captain radioed his last, brief words to Kuala Lumpur, in which he did not indicate that anything was wrong with the signaling system or the plane as a whole.
During a news conference Sunday, Defense Minister Hishammuddin Hussein, who is also the acting minister of transportation, gave a terse answer: “Yes, it was disabled before.”
The fate of the plane and the people it carried has become a formidable riddle, raising questions about possible terrorism, the identities of passengers and crew members, and aviation technology. It also has led to searches of enormous areas that include the Indian Ocean and rugged, remote terrain in Asia.
“It’s something of the scope I’ve never seen before,” Commander William Marks, the spokesman for the US Navy Seventh Fleet, which sent two guided-missile destroyers to join the search, said in a telephone interview. Of the size of the Indian Ocean, he said: “Essentially, it’s like looking for a person somewhere between New York and California. It’s that big.”
Malaysian officials on Sunday briefed representatives from 22 countries that could help search along the two corridors where satellite data indicate the plane may have wound up, having flown up to six hours after its disappearance beyond the range of military radar in western Malaysia.
Hishammuddin said Malaysia would also ask the United States, China, and other countries to provide satellite data.
But establishing what happened to the plane also depends on reconstructing events in the cockpit in the early morning of March 8, when the jet was passing over the Gulf of Thailand between northern Malaysia and southern Vietnam.
At that time, its communications links were severed and it changed direction, flying across the Malay Peninsula and out over the Strait of Malacca.
Given the complexity of that feat, experts and US government officials say that experienced aviators, possibly one or both of the pilots, were probably involved, either willingly or under coercion.
The plane took off at 12:41 a.m. on March 8, carrying 239 people headed for Beijing, and reached a cruising altitude of 35,000 feet at 1:01 a.m. Six minutes later, at 1:07 a.m., the Malaysian authorities say, the plane sent its last ACARS message, which reported nothing amiss.
Investigators have not said how they concluded that the system was disabled or when they believe that took place. But Prime Minister Najib said it shut down just before the jet reached the east coast of the Malay Peninsula, which independent radar tracking recorded at 1:08 a.m.
The authorities have not specified what time the last verbal exchange between the cockpit and the air traffic controllers took place.
But Hishammuddin’s statement means it would have occurred between 1:08 a.m. and 1:21 a.m., when the plane’s transponder stopped transmitting and ground control lost contact with the jet.
The sequence of events does not rule out the possibility of someone taking control of the cockpit and forcing the pilot to disable the system. But if that is what happened, it means the hijacker would have had to seize the cockpit in the first 26 minutes of the flight.
On a modern aircraft, it would be unlikely that a pilot would miss warning indications from onboard monitors that ACARS had malfunctioned or been disabled, said Cengiz Turkoglu, a senior lecturer in aeronautical engineering at City University London who specializes in aviation safety.
“I think they would certainly notice it,” Turkoglu said. “ACARS system failure or downgrading would be alerted, the crew would be alerted.”
Turkoglu, emphasizing that a great deal was still unknown, said the accumulating evidence on the plane’s disappearance appeared to point to a deliberate act. “There is an argument that something, somebody, who has the expertise, had something planned,” he said.
The Malaysian authorities have not singled out the pilots or crew members as the only potential suspects. Officials said Sunday that they would scrutinize the backgrounds of all passengers and crew members onboard, as well as ground crew and engineers who worked on the Boeing 777 jet.
Soon after the plane disappeared, FBI agents “scrubbed” the names of the pilots and passengers, including two Iranian men who traveled on stolen passports, to determine whether they had any connections to terrorists. They have found no such connections, officials said Sunday, while cautioning that the home countries of some of the passengers had not yet supplied full background checks on their citizens aboard the plane.
Until Najib’s announcement about the likely course of the plane, many aircraft and ships were devoted to scanning the seas off Malaysia’s east coast — the opposite direction from the new focus of the hunt.
“Malaysian officials are currently discussing with all partners how best to deploy assets along the two corridors” indicated by satellite data, the Malaysian transit ministry said in a statement. “Both the northern and southern corridors are being treated with equal importance.”