At 1126:36, the PM stated, "speed," and the PF replied, "target speed one three seven."[1] At 1126:38, the MCP-selected airspeed changed to 137 knots. At this time, the airplane was about 2.9 miles from the runway, descending through 1,300 ft msl at an airspeed of about 165 knots and a descent rate of about 1,000 fpm. By this point, the flight crew should have been able to clearly see the precision approach path indicator (PAPI)[2] lights; the PAPI indication would have been four white lights, showing that the airplane was significantly above the PAPI glidepath angle of 2.98°.
At 1126:40, the PF called out "flight director off," and the PM replied, "okay." According to quick access recorder (QAR) data,[3] at 1126:43, the left (PF's) flight director (F/D) switch was turned off, and the right (PM's) F/D switch remained on.[4] There were no further changes in the F/D switch positions for the duration of the recording. At 1126:44, the PM stated, "it's high," and over the next 8 seconds, the airplane's descent rate increased from about 1,000 to 1,500 fpm. At 1126:52, the PM stated, "one thousand," and the PF replied, "check." At 1126:54.9, the airplane was about 2.1 nm from the runway when it descended through 1,000 ft radio altitude[5] (RA) at an airspeed of about 151 knots with a descent rate of about 1,500 fpm. When it descended through 1,000 ft RA, the airplane was 243 ft above the altitude for a 3° glidepath, and the PAPI indication was four white lights. Table 1 lists selected events during the last 1,000 ft of the approach.
- ↑ Target speed for the approach was 132 knots (Vref) plus 5 knots, or 137 knots.
- ↑ A PAPI system consists of a row of four light units installed on the side of the runway that provide visual glidepath indications. The on-glidepath angle (typically about 3°) indication is two red and two white lights. Other light combinations indicate when an airplane's position is above the glidepath (four white), slightly above (three white and one red), slightly below (three red and one white), and below (four red). According to the Federal Aviation Administration's (FAA) Aeronautical Information Manual, PAPI lights are visible from about 5 miles during the day and up to 20 miles at night.
- ↑ The QAR data were used to determine the flight director switch positions because it recorded the switch positions once per second while the FDR recorded them once every 4 seconds.
- ↑ It is also possible that the PM rapidly (in less than 1 second) cycled his F/D switch off and then back on before he turned off the PF's F/D switch.
- ↑ Radio altitude is the height of an airplane above terrain immediately below the airplane as measured by a radio altimeter.
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