Epic failures: 11 infamous software bugs

Celebrate 'Debugging Day' by remembering these monster problems from the past

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Multidata Systems/Cobalt-60 overdoses

Unfortunately, the Therac-25 disaster wasn't the last software-related radiation therapy failure. Fifteen years after the Therac-25 incident, a Cobalt-60 machine in Panama's National Cancer Institute overdosed more than two-dozen patients with gamma radiation.

As with the Therac-25, the Cobalt-60 system was an accident waiting to happen. Unlike the Therac-25, the Cobalt-60 was an old, overused and undermaintained piece of hardware. The software that ran it was an aftermarket program from Multidata Systems, because the Panamanian hospital could not afford what the machine's manufacturer, Theratronics, charged.

Two of the technicians who operated the Cobalt-60 had quit, leaving the rest to work 16-hour days to keep up with treatments. Very sick patients would sometimes wait four to six hours a day for scheduled treatments.

Overworked and tired technicians requested some software maintenance, but management overlooked their requests. Somewhere along the line, the technicians hit upon a more efficient way to line up the shields that defined the radiation's target. It wasn't in the manual, but it seemed to work. Unfortunately, if you lined up the shields in a particular order, an obscure bug in the Multidata software meant that the patients were overirradiated. Because of massive overwork and undersupervision, the process went on for seven months.

By the time Multidata Systems issued an advisory about a "data entry sequence that creates a self-intersecting shape outline" in mid-2001, it was too late for many patients. The exact death toll is hard to calculate -- these were very sick patients even before their treatment -- but it's a tragic mess-up by any measure.

Osprey aircraft crash

Two weeks before Christmas in 2000, a U.S. Marine Corps Osprey, a hybrid airplane and helicopter, suffered a hydraulic system fault that should have been remedied without loss of life. A hydraulic line broke in one of the two engine cases as the Osprey was shifting from airplane to helicopter mode for landing.

According to the Marine Corps major general who presented reports during the investigation of the incident, the trouble was "compounded by a computer software anomaly." The flight-control computer stopped the rotation of the engine pods when it detected the hydraulic failure.

The pilots went through the normal procedure and pressed the primary reset button to re-engage the pods. At this point, both prop rotors went through "significant pitch and thrust changes," which led to a stall. The plane crashed into a marsh and killed all four Marines onboard.

The nature of the software flaw is still hard to track down: Boeing and Bell Helicopter made the Osprey, and Boeing's spokesman said only that changes were made in the software. Requests for details were referred to the government, and as of now, the explanation has not been forthcoming.

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