A Labeling Band on a Single Wire Caused the Dali Blackout and Key Bridge Collapse, NTSB Finds

NTSBgov, Public domain, via Wikimedia Commons

A misapplied labeling band on a single signal wire caused the electrical failure that led to Dali’s collision with Baltimore’s Francis Scott Key Bridge in March 2024, killing six road workers, according to the National Transportation Safety Board’s newly released findings.

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Investigators determined that the label prevented the wire from fully connecting inside a terminal block, triggering an unexpected breaker trip and a complete loss of propulsion and steering as the 984-foot ship left Baltimore Harbor. As NTSB Chairwoman Jennifer Homendy explained, “The Dali, at almost 1,000 feet, is as long as the Eiffel Tower is high… Finding this single wire was like hunting for a loose rivet on the Eiffel Tower.”

The blackout struck at 0129 on March 26, cutting power to key systems. The ship veered toward Pier 17, and despite efforts by pilots and crew, the vessel struck the Key Bridge, causing the central span to collapse into the Patapsco River. Six workers died, one was seriously injured, and an inspector survived unharmed.

The NTSB concluded the cause was the “loss of electrical power (blackout), due to a loose signal wire connection… stemming from the improper installation of wire-label banding,” and cited additional contributing factors, including insufficient bridge protections and a lack of “effective and immediate communications” to warn workers.

The investigation also identified broader safety issues—from an engine configuration vulnerable to shutdowns, to the use of a non-redundant flushing pump for generator fuel service. Homendy emphasized that “this was preventable,” noting that infrared thermal imaging likely would have detected the faulty connection during routine maintenance.

The collapse underscored how vulnerable older bridges are to impact from today’s much larger ships. The Key Bridge opened in 1977; the Dali is roughly ten times the size of the vessel that caused only minor damage in a 1980 incident at the same span.

Nationwide, the NTSB has urged 30 U.S. bridge owners to assess the risk of vessel strikes and implement countermeasures. Quick action by pilots and Maryland authorities to halt traffic prevented further loss of life.

Damage to the Dali exceeds $18 million, and rebuilding the Key Bridge is expected to cost up to $5.2 billion, with completion projected for late 2030.

The NTSB issued 18 new safety recommendations across the maritime and infrastructure sectors, alongside earlier urgent calls for national bridge-vulnerability assessments and risk-reduction plans.