Throughout the roughly four hours after the jet dropped from civilian radar screens, these people said, the link operated in a kind of standby mode and sought to establish contact with a satellite or satellites. These transmissions did not include data, they said, but the periodic contacts indicate to investigators that the plane was still intact and believed to be flying.

Investigators are trying to determine, among other things, whether the plane may have landed in an unknown location at some point during the period under scrutiny, these people said.