The NTSB said on Tuesday a loose wire caused a power failure on the 984-foot cargo ship Dali, leading to its March 2024 collision with Baltimore’s Francis Scott Key Bridge that killed six construction workers and destroyed the span.
The investigation found a single loose wire in the electrical system caused a breaker to unexpectedly open, launching a sequence of events that led to two vessel blackouts and a loss of propulsion and steering.
The National Transportation Safety Board in its final conclusions on the cause of the accident found wire-label banding prevented the wire from being fully inserted, causing an inadequate connection.
NTSB Chair Jennifer Homendy compared the painstaking search for the wire to finding a single loose rivet on the Eiffel Tower. The NTSB and the ship's manufacturer HD Hyundai Heavy 329180.KS had to test thousands of wires to find the problem, she added. "It's like finding a needle in the haystack."
The board also said contributing to the collapse was the lack of countermeasures to reduce the bridge’s vulnerability from impacts by ocean-going vessels, which could have been implemented if a vulnerability assessment had been conducted by the Maryland Transportation Authority.
A replacement bridge was initially estimated to cost $1.7 billion to $1.9 billion and be completed by late 2028. On Monday, state officials said they now expect the bridge will cost $4.3 billion to $5.2 billion and open to traffic only in late 2030. They cited a new pier protection system and a new longer, higher design as reasons for the increased costs.
The board staff said they recommended operators complete periodic inspections of high-voltage switchboards and proposed changes that would allow ships to more quickly recover from a loss of power.
The NTSB has said previously the Dali lost electrical power several times before the crash into the Key Bridge, including experiencing a blackout during in-port maintenance and shortly before the crash.
Power outages can happen on the water and the NTSB made numerous new recommendations to prevent catastrophic collisions, including to the US Coast Guard. It also called on Hyundai Heavy to incorporate "proper wire-label banding installation methods."
In response to questions on the NTSB findings, HD Hyundai said in a statement it delivered a safe, seaworthy vessel in 2015 with automated systems and critical redundancies to swiftly respond to blackouts but "unfortunately, the owner and operator circumvented these safeguards."
The company added that when it delivered the ship "there was no indication that any wire was loose" and said if any wire were to come loose "over the course of a decade, through vibrations or otherwise, the owner and operator should have detected that in a routine inspection and through normal maintenance."
The Key Bridge, like many other bridges, was not equipped with a warning system to prevent motorists from driving onto the bridge in the event of a hazard.
In March, the board called for urgent safety assessments of 68 bridges in 19 states including crossings like the Golden Gate Bridge, Chesapeake Bay Bridge, Brooklyn Bridge and George Washington Bridge. The NTSB recommended on Tuesday major bridge owners consider adopting motorist warning systems capable of activating when a threat is identified to immediately stop motorists from entering the bridge in an emergency.
The review focused on bridges built before 1991 and frequented by ocean-going vessels that have not undergone vulnerability assessments.
The NTSB said last year the Dali lost power about four minutes before the crash when electrical breakers unexpectedly tripped, causing a loss of power to all shipboard lighting and most equipment when it was 0.6 mile (1km) from the bridge.
The FBI is conducting a criminal probe into the collapse.
Homendy said some of the ship personnel are still in the United States.