Washington plane crash: Investigation reveals dozens of meters of difference between military helicopter's altimeters

The National Transportation Safety Board (NTSB) held investigative hearings from Wednesday to Friday, with in-depth questioning of experts and representatives of the various parties (companies, regulators, air traffic controllers, etc.) involved in the accident.

As early as February 14, the NTSB reported a "discrepancy" in the helicopter's altitude based on flight recorder data. Agency Director Jennifer Homendy revealed that, shortly before the collision, the helicopter pilot reported an altitude of 300 feet, while the instructor pilot reported 400 feet.

"Neither pilot commented on the altitude discrepancy," she noted. "At this point, we don't know why there was a discrepancy between the two." "At the time of the collision, the Black Hawk was at 278 feet. But I want to caution that this does not mean that […] that's what the Black Hawk crew was seeing on the barometric altimeters in the cockpit," she said, citing "conflicting information in the data."

As part of the investigation, the hearings revealed this week, tests were conducted on three Sikorsky Black Hawk Limas, belonging to the same battalion. They revealed discrepancies between the altitude displayed by the radar altimeter and the barometric altimeter installed on the aircraft.

In a "controlled environment, the difference was within the tolerated limit of 20 to 55 feet (but), once the rotors were turning and producing lift and thrust, the altimeter (barometric) readings dropped significantly and remained so for the duration of the flight," explained Marie Moler, one of the investigators, specifying that a "difference of 80 to 130 feet," or 24 to 40 meters, had been noted.

It's a "very significant" difference in this case, Jennifer Homendy insisted to reporters. "A difference of 100 feet is significant," she added. Indeed, in the section where the collision occurred, the helicopters were supposed to fly at a maximum altitude of 200 feet.

"I'm concerned. There's a possibility that what the crew saw was very different from what the altitude actually was," she continued. "That's something we'll continue to look into," she said. Criticism had also emerged after the crash, when it emerged that the same controller was handling helicopter traffic and some airplane traffic in the tower that evening.