A computer that monitored drilling operations on the Deepwater Horizon had been freezing with a "blue screen of death" prior to the explosion that sank the oil rig last April, the chief electronics technician aboard testified Friday at a federal hearing.

"Blue screen of death," or BSOD, is a term most often used to describe the display shown by Microsoft Windows after a serious crash that has incapacitated a PC.

In his testimony Friday, Michael Williams, the chief electronics technician aboard the Transocean-owned Deepwater Horizon, said that the rig's safety alarm had been habitually switched to a bypass mode to avoid waking up the crew with middle-of-the-night warnings.

Williams said that a computer control system in the drill shack would still record high gas levels or a fire, but it would not trigger warning sirens, according to numerous reports, including stories published by the New York Times and New Orleans' largest daily, the Times-Picayune.

Williams, who has filed a multi-million dollar federal lawsuit against Transocean, also said that five weeks before the April 20 explosion, he had been called to check a computer system that monitored and controlled drilling.

The machine had been locking up for months, Williams said, producing what he and others on the crew called a "blue screen of death." "It would just turn blue. You'd have no data coming through," Williams said today, according to the New York Times' story.

With the computer frozen, the driller would not have access to crucial data about what was going on in the well.

Williams testified before a six-person federal panel in Kenner, La., a New Orleans suburb. Government investigators have been questioning workers and executives of both Transocean, the rig's owner, and BP, which leased it to drill wells in the Gulf of Mexico. Others have testified this week about a litany of problems on the rig, including power losses, leaking emergency equipment, and cut corners that may have contributed to the explosion.

The April disaster left 11 dead and resulted in the largest oil spill in U.S. history.

Williams survived the explosion and resulting fire on the rig by leaping into the water. While he did not identify the operating system running the balky computer, the phrase "blue screen of death" is typically used to describe a Windows crash.

Microsoft declined to comment on Williams' testimony and characterization of the crash screen. Transocean did not respond to e-mail seeking comment.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer or subscribe to Gregg's RSS feed . His e-mail address is gkeizer@ix.netcom.com.