NTSB Releases Preliminary Report on Francis Scott Key Bridge Collapse

The National Transportation Safety Board (NTSB) has released a preliminary report on the March 26, 2024, collapse of the Francis Scott Key Bridge. At approximately 0129 Eastern daylight time, the 947-foot-long Singapore-flagged cargo vessel Dali, carrying 4,680 containers (56,675 metric tons), lost electrical power and propulsion while departing Baltimore Harbor. The resulting collision with the southern pier of the Key Bridge caused a significant portion of the bridge to collapse into the river, with parts falling onto the vessel’s forward deck.

A seven-person road maintenance crew from Brawner Builders, contracted by the Maryland Transportation Authority (MDTA), and an inspector from Eborn Enterprises, a sub-consultant to the MDTA, were on the bridge at the time. The inspector escaped unscathed, while one crewmember survived with serious injuries. Tragically, six construction crew members were fatally injured. One of the 23 individuals aboard the Dali was also injured.

Cause of Accident

At around 0125, 0.6 miles from the Key Bridge, the Dali experienced an unexpected electrical failure when key breakers tripped, cutting power to essential equipment, including the main engine cooling water pumps and steering gear pumps. Despite generators 3 and 4 continuing to supply power, the loss of cooling and steering systems caused the main engine to shut down, leaving the vessel without propulsion or steerage.

The crew briefly restored power at 0126, but a second blackout occurred just 0.2 miles from the bridge. Efforts to regain control, including deploying an anchor and calling for tug assistance, were insufficient. The senior pilot ordered hard port rudder, but the maneuver was ineffective without propulsion. At 0129, the Dali collided with pier no. 17 of the Key Bridge at 6.5 knots, causing six spans of the bridge to collapse.

The Dali had also experienced an electrical loss the day before the disaster, and the NTSB is investigating whether this in-port blackout influenced the events of the accident voyage.

The Dali’s route on March 26, from the first blackout to its collision with pier no. 17 of the Key Bridge, is depicted. The lower right of the image labels the location and approximate size of two of the bridge’s protective “dolphins,” which are sheet pile and concrete structures designed to safeguard the bridge’s piers. Source: NTSB.gov

Pier Protection

When the Key Bridge was constructed, four large protective dolphins were installed to safeguard piers 17 and 18. Dolphin no. 1, located about 491 feet west of pier 17, featured a 25-foot-diameter sheet pile filled with concrete and reinforced with rubber fenders. Additionally, piers 17 and 18 were surrounded by a crushable concrete box and timber fender system. During the incident, the Dali struck pier 17 and its fendering system but did not impact dolphin no. 1. The collision caused significant damage to the fendering systems of both piers 17 and 18.

The Key Bridge, along with the locations of piers 17 and 18, is depicted. Insets provide detailed views of dolphin no. 1 and the fendering system surrounding pier no. 17. Source: NTSB.gov
Locations of the dolphins in relation to the Dali, the Key Bridge, and Fort McHenry Channel. Source: NTSB.gov

Ongoing Investigation

The NTSB is actively investigating the design and operation of the Dali’s power distribution system. Damage to the vessel will be further examined once it is cleared of debris and moved to a shoreside facility.

The NTSB is collaborating with relevant parties to assess bridge safety and evaluate the need for enhanced pier protection. The MDTA is reviewing potential upgrades for the Gov. William Preston Lane Jr. Memorial Bridge (Bay Bridge) near Annapolis.

The investigation includes examining pier protection improvements on other bridges that have collapsed due to marine vessel strikes, such as the Sunshine Skyway Bridge in Tampa Bay, Florida; the Queen Isabella Causeway Bridge near South Padre Island, Texas; and the I-40 Bridge near Webbers Falls, Oklahoma.

Planned interviews with bridge experts, waterways management personnel, marine safety and highway regulators, and vessel operators will support the investigation. The NTSB continues a detailed analysis of the voyage data recorder (VDR) bridge audio and validation of VDR parameters.

Key areas of investigation include the propulsion and electrical systems of oceangoing vessels, the frequency and causes of vessel contacts with bridges, and mitigation measures such as vessel-size restrictions, vessel-assist tugs, and bridge-pier protection.

The NTSB’s comprehensive investigation aims to determine the probable cause of the accident and enhance future safety measures.

Alexander Mitchell
Alexander Mitchell
Pilot on the B-767, international and overwater operations. Accomplished SIGINT/LLVI operator with five years of diverse experience in strategic and tactical operations. Adept in handling confidential information and situations with discretion. Respected leader, providing purpose, motivation, and direction focused on achieving and exceeding company goals.

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