The final partial transmission from the missing Boeing Co. 777-200ER, which disappeared from civilian radar on March 8, "originates with the aircraft for reasons not understood," said Chris McLaughlin, senior vice president of Inmarsat PLC, which operates the satellite.
The company is investigating the partial ping—or digital handshake between the jet and the satellite—as "a failed login" to its satellite network or as a "potential attempt by the system [aboard the aircraft] to reset itself," Mr. McLaughlin said.
The cause of the partial ping could have several possible explanations, he added, but that human interaction with the satellite communications system had been ruled out.
"We're not looking at this [partial ping] as someone trying to turn on the system and communicate," he said.
The partial ping is the latest in a series of clues that have presented new questions for investigators as they try to piece together what happened to the missing aircraft and the 239 people aboard.
Unlike the partial final ping initiated by the aircraft, the earlier, roughly hourly contacts originated as part of automated communications between Inmarsat ground stations, its satellite and the jet. Those transmissions are intended to ascertain if the jet is able to send and receive information.
A statement released earlier Tuesday by Malaysian authorities indicated the U.K. Air Accidents Investigation Branch determined there was "evidence of a partial handshake between the aircraft and ground station" that followed the last complete ping eight minutes earlier.
Investigators said "at this time this transmission isn't understood and is subject to further ongoing work," but didn't elaborate.
Mr. McLaughlin in an interview said Inmarsat's engineers and investigators were trying to understand the conditions that could cause a final incomplete ping, but added that this "does not affect the plot for the probable end location of the flight" in the southern Indian Ocean.
After the jet disappeared from radar, it linked up roughly once every hour for six hours with a satellite operated by Inmarsat. By analyzing specific features of these digital handshakes between the jet and the satellite, Inmarsat officials were able to plot a direction and general course for Flight 370.
By the time the next regularly scheduled ping was supposed to occur, nearly an hour later, "the aircraft no longer was able to communicate" and presumably had gone down, Malaysia's Defense Minister and Acting Transportation Minister Hishammuddin Hussein minister told reporters Tuesday by computing the plane's estimated speed, fuel consumption and other factors, investigators are trying to project the most likely point at which it hit the water.
Deciphering the reasons behind the partial handshake, according to people familiar with the technical details, could be an important step toward understanding what aircraft systems were doing shortly before impact.
Potential causes include electrical system fluctuations and flight maneuvers, say people familiar with the technical details.
To better understand Inmarsat's data and analysis, Malaysian authorities on Tuesday said they had set up "an international working group, comprising agencies with expertise in satellite communications and aircraft performance."
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