Accident investigators are seeking to determine the accuracy of cockpit altimeter readings presented to pilots of the Sikorsky UH-60 Black Hawk that collided with a MHIRJ CRJ700 regional jet near Ronald Reagan Washington National airport on 29 January.
During an investigation update on 14 February, NTSB officials say they are yet unable to determine what altitude was shown on the Black Hawk’s altimeters because that data was not captured by the aircraft’s flight data recorder (FDR).
But the FDR did reveal an invalid figure for “pressure altitude”, which feeds the cockpit altimeters and other systems, says NTSB branch chair Sean Payne.
“This is bad data,” Payne says. “We are working to determine if this bad data for pressure altitude only affected the FDR, or if it was more pervasive throughout the helicopter’s other systems.”
“We will have an answer to what altitude the pilots saw in their gauges as they were flying,” he adds.
The Black Hawk struck the CRJ700 at 20:48 as the passenger jet was moments from landing at Reagan National. The collision sent both aircraft plummeting in the Potomac River, killing all 64 people on the CRJ700 and all three crew on the Black Hawk.
Investigators are confident, based on radio altimetry data derived from the FDR, that the Black Hawk was 278ft over the Potomac River when it struck the CRJ700, says NTSB chair Jennifer Homendy.
The NTSB is “looking at the possibility of there being bad data” and whether the cockpit altimeters were showing inaccurate altitude, she says.
Answering that question is critical to understanding why the Black Hawk pilots were flying so high. The helicopter was traversing a corridor in which it was prohibited from exceeding 200ft unless instructed by air traffic control.
Homendy reveals more details about circumstances leading to the accident, including that the Black Hawk pilots were likely using night-vision googles. Investigators are working to determine if those goggles affected the pilots’ ability to see the passenger jet.
Homendy also says that 5min before the collision, prior to entering the 200ft-maximum-altitude corridor, the pilot flying the Black Hawk indicated that the aircraft was at 300ft, while the instructor pilot indicated being at 400ft. “We don’t know why there was a discrepancy between the two,” Homendy says.
Just 17sec prior to impact, a controller instructed the Black Hawk to “pass behind the CRJ”, though that command “was stepped on” by a 0.8sec “mike key” from the Black Hawk and may not have been received by its pilots, she adds.
Additionally, the CRJ700’s pilots had received an audible “Traffic Traffic” warning from their jet’s Traffic Collision Avoidance System. After that, just 1sec before the impact, the CRJ700 “began to increase its pitch, reaching 9° nose-up,” says Homendy. “The CRJ elevators were deflected near their maximum nose-up travel.”
