The opening day of the National Transportation Safety Board’s marathon public hearings into the deadly midair crash between an Army Black Hawk helicopter and American Airlines passenger jet in January offered new details that could explain why the two aircraft were on a collision course.

The N.T.S.B. is not expected to issue their final conclusions and recommendations from the investigation until early next year. Still, the evidence, testimony, and materials that were released on Wednesday illustrated a number of problems that are likely to draw attention from regulators and lawmakers eager to close safety loopholes that allowed the fatal crash to occur.

The hearing, which lasted around 10 hours, was technical and at times testy, with the morning focused on the helicopter and the possibility that the pilot of Black Hawk was unable to know with precision just how high up in the air she was flying. The afternoon panels examined the crowded airspace around Ronald Reagan National Airport near Washington, D.C., where the crash occurred.

Hearings on Thursday and Friday are expected to delve deeper into air traffic control procedures at the airport, how the relevant agencies collect and assess safety data, and the role that advanced collision avoidance technology could play in ensuring such crashes don’t occur in the future.

Here are some of the takeaways from the hearing and the new documents released by the N.T.S.B.

Investigators have zeroed in on whether the helicopter pilot was misled by her instruments.

Data from the crash showed that at least one barometric altimeter, the main instrument that measures altitude in the Black Hawk helicopter, was recording a flying height 80 to 100 feet lower than its true altitude. And under testing, the N.T.S.B. found that the altimeters could be off by up to 130 feet on Black Hawks flying over the Potomac River, which the helicopter and jet were flying over when they collided.

That could have caused the helicopter crew to believe they were flying at a safer, lower altitude when they were actually headed straight into the jet’s path.