The NTSB is investigating the January 29 midair collision between a U.S. Army Black Hawk helicopter and an American Airlines regional jet in D.C. Preliminary findings indicate that the helicopter crew might not have received critical air traffic control instructions, potentially due to a 'stepped on' radio transmission. Furthermore, discrepancies in altitude readings between the helicopter's pilots are also under scrutiny. All 67 individuals on both aircraft perished, marking it as the deadliest aviation accident since 2001. A final report may take over a year to complete as the investigation continues.