Investigators with the USA’s National Transportation Safety Board say an army helicopter was roughly 100ft above the authorised flight ceiling for rotorcraft in the area when it impacted a commercial airliner in Washington, DC.
The 29 January incident killed 67 people when a Sikorsky UH-60 Black Hawk operated by the US Army collided with a PSA Airlines MHIRJ CRJ700 on approach to Washington’s Reagan National report.
Initial data from open source flight tracking and statements from senior government officials indicated the Black Hawk may have been operating outside its approved flight corridor, which included a hard ceiling of 200ft in the incident area along the Potomac River.
Unofficial estimates placed both aircraft at 325ft when the collision occurred.
The army says a standard altitude limit of 200ft is imposed on rotorcraft using helicopter Route 4 over the Potomac River to ensure safe separation distances with the many commercial aircraft operating around Reagan National. A description of the route on FAA navigation charts directs aviators to descend below 200ft north of the Woodrow Wilson bridge, which sits approximately 3 miles (5km) south of the crash site.
Initial results of the NTSB investigation into the deadly crash appear to support that view. The agency on 4 February said a review of air traffic control data from Reagan National indicated the UH-60 was roughly 100ft outside its altitude restriction.
“This data showed the Black Hawk was at 300ft on the air traffic control display at the time of the collision,” the NTSB says.
The data was collected from the Potomac Consolidated Terminal Radar Approach Control (TRACON) facility in Warrenton, Virginia. TRACON combines information from multiple ground-based radar sensors and ADS-B data, according to the NTSB, “providing the best quality flight track data to air traffic control”.
Notably, the TRACON flight data is rounded to the nearest 100ft, meaning the UH-60 could have been above or below the 300ft level.
Since the 29 accident over the Potomac River, the Federal Aviation Administration has indefinitely suspended the use of helicopter corridors along the urban waterway, which features some of the busiest airspace in the country.
Although it has already recovered the rotorcraft’s combined cockpit voice and flight data recorder, the NTSB says it will need to collect additional evidence from the remnants of the Black Hawk’s fuselage to verify the existing data points.
The agency does not specify what additional pieces of information it is seeking to reach a definitive conclusion.
However, one possibility may be related to the angle of impact between the two aircraft.
Available flight tracking indicates the collision may have taken place closer to the west bank of the Potomac, some distance away from the prescribed helicopter corridor. Standard navigation charts from the FAA indicate helicopter Route 4, along which the UH-60 was travelling, follows the eastern bank of the Potomac.
Just before the collision, the PSA CRJ700 is known to have diverted northeast at the direction of air traffic control to land at an alternate runway – number 33 – rather than Regan National’s primary runway. Flight tracking estimates based on multilateration indicate the Black Hawk may have deviated westward from Route 4 – possibly in an attempt to avoid the inbound commercial traffic.
According to radio transmissions archived by LiveATC, the helicopter crew confirmed it had traffic “in sight” and requested visual separation – a procedure under which the pilot is responsible for maintaining safe distance from the other aircraft.
The wreckage of the UH-60 is expected to be recovered from the Potomac River in the coming days. The NTSB has already located flight data and cockpit voice recorders from the incident CRJ700, which was operating as American Airlines flight 5342.
Separately, investigators are also reviewing maintenance records associated with both aircraft.
The aircraft systems group continued to review maintenance paperwork for the CRJ700 and the helicopter airworthiness group continued to review maintenance records for the Black Hawk.
NTSB investigators continue to transcribe the cockpit voice recorders for both aircraft. Synchronization work for the Black Hawk flight data recorder and cockpit voice recorder is ongoing.
The army has said the UH-60 was conducting a routine night operations proficiency flight when the crash occurred.
