Investigators testifying at a hearing into the January's mid-air crash in Washington DC suggest faulty altitude data may have led to a miscalculation.

The National Transportation Safety Board will question witnesses Thursday about air traffic control training and collision avoidance technology, two key parts of the investigation into January’s deadly midair collision at Ronald Reagan Washington National Airport.

The hearing, the second of three days, is focused on the training guidance of the parties involved in the Jan. 29 incident that resulted in the deaths of 67 people. NTSB started the daylong hearing examining the responsibilities and readiness of DCA's air traffic controllers.