Cockpit voice recorder data from the UPS A300-600F freighter that crashed on approach to Birmingham, Alabama, before sunrise on August 14 reveal an impact with either trees or terrain 4 seconds after one of the two pilots called out, “runway in sight”.
The short time span between runway sighting and ground or tree collision likely indicates that the pilots were either using a modified instrument approach procedure for Runway 18, or that there was an error or confusion leading them to believe the aircraft was at a higher altitude.
According to instrument approach charts for the localizer approach to Runway 18, the non-precision approach which UPS Flight 1354 was using to land that morning, the aircraft is not to descend below 556 ft. above the ground (1,200 ft mean sea level) until the pilots visually spot the runway “environment” through the windscreen.
U.S. National Transportation Safety Board member Robert Sumwalt, during a press briefing on August 16, said there were sounds “consistent with an impact” at 9 seconds before the cockpit voice recorder (CVR) stopped working, though he did not specify if those sounds were the aircraft striking tree tops in a neighborhood along the final approach, or the impact of the A300 on a hillside approximately 0.5 mi. before the runway end. He did say investigators looking at the A300’s Pratt & Whitney PW4158 engines determined that it had ingested “trees and dirt”.
Either way, the A300 was much lower than it should have been on the localizer 18 approach if pilots sighting the runway only 4 seconds before the sounds of an impact with an object at or near ground level. Typically, pilots begin descending from the minimum descent altitude (556 ft. AGL in this case) upon sighting the runway, which means that 4 seconds after sighting the runway, the aircraft should have been hundreds of feet above terrain.
For a localizer approach, pilots use the ground-based localizer for left-right guidance and the aircraft’s barometric altimeter for altitude information. Without vertical guidance, the approach is considered “non-precision” and has higher minimums (the lowest altitude to which the aircraft can descend without pilots having the runway in sight) compared to a precision approach. Birmingham’s other runway has an instrument landing system (ILS) precision approach with vertical and horizontal guidance, but the runway was not usable that morning due to work in progress on its centerline lighting system, said Sumwalt.
When completing the approach visually, pilots generally use the precision approach path indicator (PAPI) system located near the runway, a row of four white or red lights that show the aircraft’s vertical position with respect to the ideal glideslope. Sumwalt says the FAA tested the PAPI after the accident and found it to be accurate.
Aircraft performance and energy appeared normal based on initial indications from the flight data recorder (FDR). Sumwalt said control inputs and aircraft flight control surfaces appear to correlate properly and engines indicated normal operations.
The aircraft’s autopilot was engaged until the last second of FDR data and the autothrottle system was engaged through the end of the data, said Sumwalt, with the recorded airspeed tracking the autoflight selected airspeed of about 140 kt., which is consistent with the expected approach speed for A300. Sumwalt noted that the CVR operated for a few seconds after the FDR stopped.
Sumwalt also reported that 3 seconds before a pilot called “runway in sight”, there were two audible “sink rate” alerts issued by the enhanced ground proximity warning system, indicating a descent rate that was outside the bounds of the expected descent rate for the speed, altitude and aircraft configuration at the time.
The NTSB plans to fly another UPS A300 on the approach to Birmingham in the next few weeks to observe the company’s procedures for using the Runway 18 localizer approach, says Sumwalt.