A coincidence of weather damage and a possible construction accident knocked Sprint’s Western U.S. network out of service for three and a half hours Monday afternoon. The outage occurred following a fiber cut near Phoenix, Ariz., which took place hours after traffic from a flooded area of California had been routed through Phoenix to enable emergency maintenance.

The “dual” fiber cut prevented the network from simply re-routing traffic around a self-healing ring, as routinely occurs in today’s public-switched telephone network. Instead, the service outage left millions of West Coast wireless, wireline and Internet customers without service, including Sprint customers, some Nextel customers, and customers of both Virgin Mobile and Qwest wireless services, which use Sprint’s network. Local phone service was not affected, but customers could not make long-distance calls and Internet access was slowed or non-existent.

“It was an unfortunate situation,” a Sprint spokesman said. Were it not for the coincidence of the maintenance and the fiber cut, however, “this would be a non-event,” he said.

Sprint crews began working Saturday in a remote area near Reno Junction, Calif., to repair a partially washed-out cable in an area affected by this winter’s heavy rains and flooding, the spokesman said. “The cable wasn’t completely out, but it needed to be repaired,” he said. “The repairs were hampered by the fact this area is not accessible by car--our techs were literally stringing fiber optic cable through the trees on Sunday night.”

The plan was to do a “hot cut”--or live transfer of traffic--onto the newly placed cable. While it was being strung, however, traffic through that area was re-routed through Phoenix, another standard procedure, the spokesman said. Before the hot-cut could be completed, however, the accidental fiber cut took place between Phoenix and Palm Springs, Calif., and the second cut on the fiber ring prevented re-routing of traffic, effectively isolating the West Coast portion of the network.

Sprint crews immediately “backed out” of the maintenance procedure to do a temporary fix near Reno to restore traffic in that segment within three hours, he said. The Arizona repair took an additional half hour.

An investigation begins today on the cause of the Arizona fiber cut, but, in all likelihood, it is the result of a construction accident.

“We know we didn’t have crews working in that area,” the spokesman said. “We have remote visibility into that area, and we know exactly where the cut occurred. Our investigators will follow standard procedure to determine what happened."