American Airlines Flight 77 departed Washington Dulles at 8:20 AM (point A in Figures 1 and 2) and reached its assigned cruising altitude of 35,000 feet at about 8:46 AM (B). The final routine radio transmission from the flight was received at 8:51 AM.

American Airlines Flight 77 was flying exceptionally low in the final seconds before it struck the Pentagon on September 11, 2001. According to the NTSB Flight Path Study, the Boeing 757 was so low to the ground that it reportedly clipped a car antenna on Washington Boulevard and severed five light poles along the highway as it approached the building. Just 0.42 seconds before impact, the aircraft was approximately 320 feet from the west wall, traveling at an altitude that placed it nearly level with the first and second floors. The aircraft actually struck the Pentagon at the first-floor level, having maintained a high-speed, low-level trajectory of approximately 530 miles per hour (460 knots). Witnesses described the plane as "skimming" the ground, and the flight data recorder indicates it was flying only a few feet above the lawn in its final moment of impact. This extremely low altitude was a result of a steep descending 330-degree turn intended to line the aircraft up with the target at maximum speed while remaining below most radar detection.