Bridge Collapse Cause

NTSB report determines reasons for Baltimore Key Bridge incident

The NTSB said in a November 18 press release that a single loose wire on the 984-foot-long containership Dali caused an electrical blackout that led to the giant vessel veering and contacting the nearby Francis Scott Key Bridge in Baltimore, which then collapsed, killing six highway workers. 

At Tuesday’s public meeting at NTSB headquarters, investigators said the loose wire in the ship’s electrical system caused a breaker to unexpectedly open -- beginning a sequence of events that led to two vessel blackouts and a loss of both propulsion and steering near the 2.37-mile-long Key Bridge on March 26, 2024. Investigators found that wire-label banding prevented the wire from being fully inserted into a terminal block spring-clamp gate, causing an inadequate connection. 

​Illustration showing how placement of wire-label banding affects the way wires are seated in their terminal blocks. (Source: NTSB)

After the initial blackout, the Dali’s heading began swinging to starboard toward Pier 17 of the Key Bridge. Investigators found that the pilots and the bridge team attempted to change the vessel’s trajectory, but the loss of propulsion so close to the bridge rendered their actions ineffective. A substantial portion of the bridge subsequently collapsed into the river, and portions of the pier, deck and truss spans collapsed onto the vessel’s bow and forwardmost container bays.

A seven-person road maintenance crew and one inspector were on the bridge when the vessel struck. Six of the highway workers died. The NTSB found that the quick actions of the Dali pilots, shoreside dispatchers and the Maryland Transportation Authority to stop bridge traffic prevented greater loss of life.

”Our investigators routinely accomplish the impossible, and this investigation is no different,’ said NTSB Chairwoman Jennifer Homendy. “The Dali, at almost 1,000 feet, is as long as the Eiffel Tower is high, with miles of wiring and thousands of electrical connections. Finding this single wire was like hunting for a loose rivet on the Eiffel Tower.

“But like all of the accidents we investigate this was preventable,” Homendy said. “Implementing NTSB recommendations in this investigation will prevent similar tragedies in the future.”

Contributing to the collapse of the Key Bridge and the loss of life was the lack of countermeasures to reduce the bridge’s vulnerability to collapse due to impact by ocean-going vessels, which have only grown larger since the Key Bridge’s opening in 1977. When the Japan-flagged containership Blue Nagoya contacted the Key Bridge after losing propulsion in 1980, the 390-foot-long vessel caused only minor damage. The Dali, however, is 10 times the size of the Blue Nagoya.