US probing 'bad data' possibly used by Black Hawk crew before deadly crash: officials

Transportation safety officials on Friday said they believe the crew of an Army Black Hawk helicopter that crashed into a passenger jet outside Washington, DC, last month were wearing night vision goggles and possibly relying on inaccurate flight data moments before the fatal collision.

Preliminary analysis of voice recordings and other black box data recovered from the crash site showed the helicopter pilot and her instructor read aloud conflicting altitudes before the collision, while some of the Black Hawk's altitude data appeared to investigators as faulty, National Transportation Safety Board officials said.

"We are seeing conflicting information in the data, which is why we aren't releasing altitude for the Black Hawk's entire route," NTSB chair Jennifer Homendy told reporters on Friday.

Homendy said investigators are confident that at the time of the crash the helicopter was at an altitude of 278 feet (85 meters) - higher than it should have been for the area. "But I want to caution," Homendy added, "that does not mean that's what the Black Hawk crew was seeing."

One of the helicopter's sources of altitude data that relies on atmospheric pressure - but is not typically used directly by pilots - was deemed by investigators as invalid.

"This altitude is calibrated using what we call standard atmospheric pressure, we have found that this parameter is not valid. This is bad data," said Sean Payne, head of NTSB's vehicle recorder data division.

The NTSB has been investigating the January 29 mid-air collision between the helicopter and the American Airlines Bombardier jet that killed 67 people in the deadliest US air disaster in more than 20 years.

The Black Hawk crew, who were on a nighttime training flight but regarded as experienced pilots, were believed to be wearing night vision goggles that could have made it difficult to distinguish the American Airlines jet from city lights on the horizon, Homendy said.

Homendy noted that the on-scene portion of the investigation into the disaster had now been finished.

Over the next week, Homendy said, wreckage will be moved from the Ronald Reagan Washington National Airport to a secure location for more detailed analysis.

Investigators will laser-scan mockups of the Black Hawk cockpit for detailed comparisons with the crashed helicopter and scrutinize whether various altimeters and other recovered data systems were functioning as designed or, for some reason, turned off deliberately.