ADDIS ABABA, Ethiopia — The captain of a doomed Ethiopian Airlines jetliner faced an emergency almost immediately after takeoff from Addis Ababa, requesting permission in a panicky voice to return after three minutes as the aircraft accelerated to abnormal speed, a person who reviewed air traffic communications said Thursday.
“Break break, request back to home,” the captain told air traffic controllers as they scrambled to divert two other flights approaching the airport. “Request vector for landing.”
Controllers also observed that the aircraft, a new Boeing 737 Max 8, was oscillating up and down by hundreds of feet — a sign that something was extraordinarily wrong.
All contact between air controllers and the aircraft, Ethiopian Airlines Flight 302 to Nairobi, was lost five minutes after it took off on Sunday, the person said.
The person who shared the information, speaking on the condition of anonymity because the communications have not been publicly released, said the controllers had concluded even before the captain’s message that he had an emergency.
The account of the cockpit communications shed chilling new detail about the final minutes before the plane crashed, killing all 157 people aboard. The crash, which has led to a worldwide grounding of Max 8s, was the second for the best-selling Boeing aircraft in less than five months.
Regulatory authorities in the United States and Canada say similar patterns in the trajectories of both planes may point to a common cause for the two crashes. But they cautioned that no explanation had been ruled out yet, and said the planes might have crashed for different reasons.
The new disclosures about the last moments of Flight 302 came as pilots were discussing what they described as the dangerously high speed of the aircraft after it took off from Addis Ababa’s Bole International Airport.
Pilots were abuzz over publicly available radar data that showed the aircraft had accelerated far beyond what is considered standard practice, for reasons that remain unclear.
“The thing that is most abnormal is the speed,” said John Cox, an aviation safety consultant and former 737 pilot.
“The speed is very high,” said Mr. Cox, a former executive air safety chairman of the Air Line Pilots Association in the United States. “The question is why. The plane accelerates far faster than it should.”
Ethiopian Airlines officials have said the crew of Flight 302 reported “flight control” problems to air traffic controllers a few minutes before contact was lost. The new account of communications between air traffic controllers and the pilot, Yared Getachew, who had 8,000 hours of flying experience, provides much more information about what was happening in the cockpit.
Within one minute of Flight 302’s departure, the person who reviewed communications said, Captain Getachew reported a “flight control” problem in a calm voice. At that point, radar showed the aircraft’s altitude as being well below what is known as the minimum safe height from the ground during a climb.
Within two minutes, the person said, the plane had climbed to a safer altitude, and the pilot said he wanted to stay on a straight course to 14,000 feet.
Then the controllers observed the plane going up and down by hundreds of feet, and it appeared to be moving unusually fast, the person said. The controllers, the person said, “started wondering out loud what the flight was doing.”
Two other Ethiopian flights, 613 and 629, were approaching from the east, and the controllers, sensing an emergency on Flight 302, ordered them to remain at higher altitudes. It was during that exchange with the other planes, the person said, that Captain Getachew, with panic in his voice, interrupted with his request to turn back.
Flight 302 was just three minutes into its flight, the person said, and appeared to have accelerated to even higher speeds, well beyond its safety limits.
Cleared by the controllers to turn back, Flight 302 turned right as it climbed further. A minute later, it disappeared from the radar over a restricted military zone.
The disaster drew immediate comparisons to the October crash of another Boeing 737 Max 8, operated by Lion Air, in Indonesia. Both took place soon after takeoff, and the crews of both planes had sought to return to the airport.
The possibility that the two crashes had a similar cause was central to regulators’ decision to ground all 737 Maxes, a family of planes that entered passenger service less than two years ago.
After the Indonesia crash, a new flight-control system meant to keep the jet from stalling was suspected as a cause. In both cases, pilots struggled to control their aircraft.
[Why investigators fear the two Boeing 737s crashed for the same reason.]
The investigation of the Ethiopian crash is still in its early stages, and safety regulators have noted that it is too soon to draw conclusions about the cause. The so-called black boxes, voice and flight data recorders that contain more detailed information about the Ethiopian flight’s final moments, arrived in France on Thursday for analysis.
Since the Indonesia crash, Boeing has been working on a software update for the 737 Max jets, expected by April. But the company and the Federal Aviation Administration face new questions over whether there should have been more pilot training as airlines added the new models to their fleets.
On Wednesday, the chairman of the transportation committee in the House of Representatives said he would investigate the F.A.A.’s certification of the 737 Max, including why the regulator did not require more extensive training.