The Army pilots whose Black Hawk helicopter crashed into a passenger jet over the Potomac River on Jan. 29 may have been misled by their instruments, causing them to believe they were at a safer, lower altitude when they were actually headed straight into the jet’s path, according to evidence that federal investigators unveiled on Wednesday.
That revelation came as the National Transportation Safety Board began three days of public hearings into the midair collision that killed 67 people, the first fatal crash involving a major American airline in 15 years.
Those hearings revealed a series of malfunctions and fateful decisions that night that heightened the dangers of an already crowded airspace over the river near Washington’s Ronald Reagan National Airport, crisscrossed by passenger jets and helicopters flown by the military and local police.
Inside the helicopter, for instance, investigators said that the Black Hawk’s instruments might have shown the pilots were flying below their actual position. The area in which the helicopter was flying did not have much room for error. Helicopters there were expected to fly in a narrow band between 100 and 200 feet above the Potomac.
Inside the airport’s control tower that night, investigators found, a single controller was handling both helicopter and airplane traffic at the time of the 8:48 p.m. crash, though the jobs are not typically combined at that hour.
Then the controller instructed the Army helicopter to go behind the American Airlines plane as it was landing, which other pilots told the N.T.S.B. was unusual. Typically, controllers tell helicopters to simply wait upriver until planes on that path pass.
The N.T.S.B. will not release its full report on the causes of the crash until early next year. But during Wednesday’s hearing, members of that board expressed frustration with the Army and the Federal Aviation Administration, which oversees the air traffic controllers.
One board member, J. Todd Inman, took issue with an Army representative’s estimate that the service would update its manuals to let pilots know about the altimeter’s problems — by September.
“You’re telling me it’s going to be two months before you tell them that there’s a discrepancy in their altitude?” asked Mr. Inman, who said that helicopters of the same model as the one that crashed flew over his home in the D.C. suburbs. “Could you hurry it up?”
Scott Rosengren, an Army engineer overseeing the modernization of Black Hawk helicopters, testified that — if he had the power — he would remove all of the Black Hawks of the type involved in the accident from the Army’s use. “If I was king for a day, I would take all Limas out of the fleet today,” he said, referring to the Black Hawk UH-60L model.
But, Mr. Rosengren said, the Army’s plan is to keep the helicopters in service, until they are gradually phased out.
The N.T.S.B. began its hearing with an animation showing the flight paths of those two aircraft, overlaid with recordings of the pilots’ conversations with air traffic control. Investigators also released transcripts of what those in each cockpit said to each other, revealing that neither seemed to have a sense they were in danger until it was too late.
The following is the agency’s chronology of how those paths converged, enabled by what appeared to be both mechanical and human factors.
The pilot of the Army helicopter was Capt. Rebecca M. Lobach, who was taking an annual proficiency test using night-vision goggles. She was joined by her instructor Chief Warrant Officer 2 Andrew Loyd Eaves and the aircraft’s crew chief, Staff Sgt. Ryan Austin O’Hara.
They started from an Army base south of Washington, and made a wide clockwise circle around the city’s suburbs. The last bit of that circle — from one to four on the imaginary clock face — would take them south down the Potomac toward their base, Fort Belvoir in Virginia, through the busy corridor in front of National Airport.
Following the rules for helicopters along that stretch of river, investigators said, Capt. Lobach took the helicopter lower. But not low enough. As it got closer to the airport the helicopter largely stayed above the required 200-foot ceiling — at times climbing higher than 300 feet — and was at 278 feet at the time of the crash. Investigators said that an examination of the wreckage indicated that at least one altimeter in the cockpit, which used barometric pressure to estimate height, may have been off.
That prompted investigators to test three additional Black Hawks, which found that the altimeters’ readings ranged from 80 to 130 lower than their true altitude when flying over the Potomac.
Army experts testified that it was not uncommon for altimeter readings to fluctuate as much as 100 feet from the true altitude of an aircraft, and that such discrepancies were not usually cause for alarm.
Kylene Lewis, an Army helicopter test pilot who testified at Wednesday’s hearing, told F.A.A. officials that in many circumstances, a 100-foot difference between separate altimeter readings on an aircraft during flight “would not be a large area of concern.”
“A couple hundred feet would be a concern in flight,” she added.
For Capt. Lobach, however, who was trying to thread her way through such a busy airspace at night, 100 feet might have made the difference between a near miss and a crash.
As her helicopter moved downriver, the American Airlines plane from Wichita was preparing to land. The air-traffic controller had asked them to switch to a relatively little-used runway — requiring them to land east to west, across the helicopter’s planned path.
That raised risks. But there was a known solution: Helicopters, unlike planes, can stop and hover. Other helicopter pilots told the N.T.S.B. that they had often been told to pause over Hains Point, at the tip of an island north of the airport, until planes on this same cross-river approach had safely passed.
“If I was southbound, I was told to hold north by Hains Point,” said Army Chief Warrant Officer 5 David Van Vechten Jr. “Not one single time ever did they let me cross the approach path” of Runway 33, where the passenger jet was landing that night. A transcript of his interview was among those released by the N.T.S.B. on Wednesday.
On Jan. 29, a single air traffic controller was handling both helicopters and airplanes. Investigators said that under normal conditions, these jobs were supposed to be handled by two separate controllers during busy daytime and early evening hours, but that they had been combined for most of the day.
This particular controller had been doing the combined jobs for an hour and 20 minutes before the crash. The person’s supervisor, who was also not named, said there had been no need to keep the duties separate, given that night’s workload, documents released by the N.T.S.B. said.
But in the helicopter, the two pilots thought he sounded busy.
“He’s got ’em stacked up tonight,” Mr. Eaves said.
“Busy,” said Capt. Lobach.
Instead of stopping the helicopter upriver to wait, the controller let them continue toward the airport, using “visual separation.” That was a technical phrase for a low-tech solution.
The onus was now on Capt. Lobach and her crew to spot the incoming airplane against the lights of the suburbs, track it and stay away. Other pilots told investigators that was difficult in this situation, especially at night. Pilots wearing goggles would have trouble distinguishing the lights of a crosscutting plane in the clutter of lights from homes and businesses behind it.
There were other planes near the airport that night. The helicopter pilots may have seen one of them, and thought it was the American Airlines plane they were looking for.
But it appears they never saw the one they hit.
Instead, their last conversation seemed to be in response to an instruction from the air traffic controller to move toward the east bank of the river, on their left.
“All right, kinda come left for me, ma’am, I think that’s why he’s asking,” the instructor pilot said.
“Sure,” Capt. Lobach said.
“We’re kinda —” the instructor said, without finishing.
“Oh-kay. Fine,” the pilot said.
“Out towards the middle,” the instructor said, probably referring to the Potomac they were overflying.
At that moment, the American Airlines plane was headed straight into their path, coming across the river from their left.
Inside that plane, the pilots also seemed unaware of the danger. Capt. Jonathan Campos tried to pull the plane’s nose up sharply only one to two seconds before the crash, N.T.S.B. investigators found.
By then, there was no time left. The paths of the two planes met over the river.
In the airport’s control center, the report said, the controller was guiding another plane through landing at the time of the accident.
The N.T.S.B.’s report said a recording of the tower then picked up the sounds of an electronic collision warning, “followed by audible reactions from other A.T.C. personnel in the tower” as the two aircraft collided in a fiery explosion.
Karoun Demirjian is a breaking news reporter for The Times.
Kate Kelly covers money, policy and influence for The Times.
David A. Fahrenthold is a Times investigative reporter writing about nonprofit organizations. He has been a reporter for two decades.
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