The U.S. National Transportation Safety Board (NTSB) is turning its attention to “bad” and conflicting altitude data and possible “stepped on” air traffic control radio communications as it continues its investigation of the fatal Jan. 29 mid-air collision between a regional jet and a U.S. Army UH-60 Black Hawk.
In a briefing conducted by NTSB chair Jennifer Homendy and vehicle recorder branch chief Sean Payne, the NTSB provided a reconstruction of the final minutes for both aircraft and additional details about the flights as they entered the airspace around Reagan National Airport (DCA) in Washington, D.C. The pilot flying the helicopter was performing a combined annual and night vision goggle qualification check ride, accompanied by an instructor and a crew chief.
The helicopter was proceeding southbound on established helicopter routes with fixed altitude restrictions. The maximum allowed helicopter altitude at the point of the collision was 200 feet (61 meters). Three minutes before the crash, the helicopter pilot flying noted an altitude of 300 ft. (91 m), while the instructor noted 400 ft. (122 m).
“Neither pilot made a comment discussing an altitude discrepancy,” Homendy said.
One-minute and 42 seconds later, the instructor told the pilot flying they were at 300 ft. and needed to descend. The pilot flying said they would descend to 200 ft.
Two minutes and 29 seconds later, the aircraft collided. The Black Hawk’s radio altitude was 278 ft. (85 m). Two seconds before the collision, the CRJ’s radio altitude was 313 ft. (95 m).
Nineteen seconds before impact, the CRJ’s traffic alert and collision avoidance system (TCAS) issued an audible warning. Seven seconds before impact, the CRJ rolled out on final to runway 33 at a radio altitude of 344 ft. (105 m).
Two seconds before impact, the CRJ’s roll was 11 degrees left wing down and nose was pitched nine degrees up. The NTSB noted that this was an elevator deflection “near the maximum” of available nose up travel. The Black Hawk was approximately 0.5 degrees nose up with a left roll of 1.6 degrees.
Homendy said NTSB investigators were seeing “conflicting” altitude data for the Black Hawk. Payne said the helicopter’s flight data recorder (FDR) did not record the barometric data and that the pressure altitude data from the FDR “is bad data,” as the standard atmospheric pressure altitude calibration’s parameter “is not valid.”
“Normally, we can use this parameter to compute the barometric altitude displayed to the pilots. Because this data is bad, we have to use other methods to make this determination,” Payne said, noting that GPS might not be helpful as “the FDR does not record GPS information.”
Further analysis will require an examination of the altimeters as well as the pitot-static and air data system. As the helicopter was badly damaged, some of this examination “will be difficult,” he said.
The NTSB also is examining radio communications between the control tower and the helicopter.
One minute and 58 seconds before impact, the tower advised the Black Hawk of a CRJ “circling” on approach to runway 33. Data from the Black Hawk’s cockpit voice recorder (CVR) “indicated that the portion of the transmission stating that the CRJ was ‘circling’ may not have been received by the Black Hawk crew.”
The Black Hawk crew responded traffic in sight and was approved for vertical separation. Thirty seconds later — 20 seconds before impact — the tower asked the Black Hawk if they had traffic in sight. An ATC “collision alert” aural warning can be heard in the background.
Three seconds after that, the tower directed the Black Hawk to “pass behind” the CRJ. Black Hawk CVR data indicates the crew may not have received the words “pass behind” as they were keying their microphone and stepped on part of the tower transmission.
The Black Hawk then again responded that it had the traffic. The instructor, working the radios, then told the pilot flying they believed the tower wanted them to turn left toward the east bank of the Potomac River.
Fifteen seconds later, the aircraft collided.
