NTSB: Misplaced Wire Label Triggered Power Failure That Caused Cargo Ship to Collapse Key Bridge

The National Transportation Safety Board revealed Tuesday that a misplaced label on a single wire contributed to the catastrophic collapse of Baltimore’s Francis Scott Key Bridge in March 2024. The nearly decade-old labeling mistake caused an intermittent electrical failure aboard the massive cargo ship Dali, which lost power and steering as it left the Port of Baltimore, leading to a fatal collision that killed six construction workers.

NTSB Chair Jennifer Homendy opened the public hearing by stressing that the tragedy was preventable. According to investigators, a sticker placed incorrectly on a signal wire during the ship’s construction prevented the wire from securing properly inside a circuit breaker. That loose connection caused the Dali’s first blackout, cutting off steering, lighting, water pumps, and the bow thruster for 58 seconds.

Although crew members restored power, they failed to manually restart a key pump needed to supply fuel to the generators. That oversight led to a second blackout just moments later, leaving the ship adrift three ship lengths from the bridge with no time to recover control.

Homendy described the difficulty the crew would have faced trying to restart the pump in near-total darkness, noting that it required traveling multiple decks down with a flashlight. The pump had been running continuously for months, even though it was designed only for maintenance and lacked a backup.

Investigators said that the ship had experienced two smaller blackouts earlier that day while still docked, including one caused by crew error.

In the seconds before impact, the Dali notified the Maryland Transportation Authority, which halted traffic on the bridge. But road crews repairing potholes on the bridge were never warned despite having more than a full minute to evacuate. Their vehicles were on the span when it collapsed, plunging into the water below. Six workers died, one survived with injuries, and an inspector narrowly escaped as the bridge fell behind him.

The magnitude of the collision was nearly five times greater than the structural capacity of the bridge’s pier, according to NTSB engineers.

Officials said the loose wire was “almost impossible” for crew members to detect given the ship’s vast size, miles of wiring, and thousands of electrical connections. The NTSB’s own simulation of the system resulted in the same wire disconnecting again.

The investigation also revealed that the Key Bridge had nearly 30 times the acceptable level of collapse risk for critical bridges under modern engineering standards — a vulnerability assessment that the Maryland Transportation Authority had never conducted. The NTSB has since identified 68 similar U.S. bridges built before 1991 that also lack up-to-date risk evaluations.

Maryland officials estimate the cost of replacing the Key Bridge at $4.3 to $5.2 billion, with a completion date expected in late 2030. That estimate is more than double previous projections.

The NTSB issued 17 safety recommendations to ship owners, bridge agencies, the Coast Guard, and industry groups to help prevent similar incidents. While not mandatory, the recommendations urge improvements in wiring inspections, bridge vulnerability assessments, and emergency communications between maritime and roadway agencies.

“Our hearts are with you,” Homendy told families of the victims as she closed the meeting. “We will work to ensure this never happens again.”

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