The ground proximity warning system on the UPS Airbus A300-600 freighter that crashed 14 August in Birmingham, Alabama issued an audible warning 16s before the cockpit voice recorder tape ends.
"Sink rate! sink rate!" the system called, moments before the aircraft plowed into trees and crashed in a field near the Birmingham-Shuttlesworth International airport, killing two pilots, according to the National Transportation Safety Board (NTSB).
Speaking at a press conference today in Alabama, NTSB member Robert Sumwalt says investigators have collected good data from the cockpit voice and flight data recorders, but he releases only snippets of information, noting the agency is still in early stages of the investigation.
The aircraft, operating UPS flight 1354 from Louisville, went down at 06:11 Eastern time (05:11 local time), breaking apart and erupting in a fire that smoldered until evening.
Sumwalt notes that the ground proximity warning system issues an alert if the aircraft strays from parameters programmed into the computer.
The captain, identified by UPS as Cerea Beal Jr. was the pilot flying during the approach to runway 18, the shorter of Birmingham's two runways. Unlike longer runway 6/24, runway 18 does not have an instrument landing system, according to AirNav.com
The aircraft was cleared to land on runway 18 two minutes before the end of the voice recorder tape.
Shortly after the ground proximity warning alert, at 13s before the end of the tape, one crew member said the runway was in sight. Nine seconds before the tape ends are sounds consistent with an impact, Sumwalt says.
The Birmingham control tower that morning was staffed by two air traffic controllers, though one was on a scheduled break when the aircraft went down, the NTSB says.
The controller who directed the accident aircraft, described by Sumwalt as "very experienced", witnessed the crash.
He told investigators he saw a bright spark - like an electrical spark from a broken power line. He also said he saw the aircraft's landing lights, then did not, then saw a "bright orange flash" and then a "red glow," Sumwalt says.
The controllers' minimum safe altitude warning (MSAW) system did not issue an alert, he adds.
Beal and the first officer, which UPS identified as Shanda Fanning, were scheduled to begin their duty period the night before with a flight from Rockford to Peoria in Illinois. The schedule then brought them to Louisville, then Birmingham, says Sumwalt.
The NSTB has been joined in the investigation by French investigators and those from Airbus.