They may have never seen the PAPIs because of weather obscuring their ability to see them. But, they had a sight line to the PAPIs until very near the end when the small hill and perhaps trees would have blocked the sight line.
Reference....
http://dms.ntsb.gov/public%2F55000%2...2F550789%2Epdf
....."Aircraft Performance Study" pages 24 and 25.....
It is of interest to know whether the PAPI lights would have been visible to the crew of flight 1354 as it approached runway 18, and if so, what light pattern would have been perceived. This problem amounts to knowing the position of the airplane relative to each of the four PAPI light beams, and identifying whether any obstructions (such as terrain) penetrated the line of sight between the PAPI and the airplane. The angle of these beams relative to the runway are defined by the (actual) PAPI glide path angle, and the (actual) aiming angles of each of the beams relative to the glide path angle.
PAPI beam solutions for both the design value of the PAPI glide path angle (3.20°), and the nominal aiming angles for a height group 3 PAPI are depicted in Figure 9 (per Table 7, the actual aiming angles are all within 0.5 minutes of arc of the nominal values, so the beam
paths depicted in Figure 9 are representative). The altitudes of the beams depicted in Figure 9 take into account the curvature of the Earth, which will increase the height of the beams as the distance from the PAPI increases, compared to the height obtained assuming a flat Earth.
Figure 9 indicates that prior to IMTOY, flight 1354 was above the PAPI glide path, and crossed below it about 0.1 nmi north of IMTOY, though at IMTOY, the PAPI display to the crew would still have been 2 white and 2 red lights (indicating on the glide path). The display would have changed to 3 red lights and 1 white light about 0.05 nmi south of IMTOY, indicating that the airplane was deviating below the glide path. The PAPI display would have changed to 4 red lights (indicating a position well below the flight path) about 0.3 nmi south of IMTOY, or about 1.7 nmi north of the runway threshold. Of course, the video analysis described in Section D-VI indicates that at this point the runway (and PAPI) would still have been obscured by clouds, and would remain so at least until the airplane descended below 1000 ft. MSL, about 1.4 nmi north of the threshold.
When the crew reported the runway in sight at about 900 ft. MSL and about 1.24 nmi north of the threshold, Figures 9 and 24 suggest that the PAPI would have been visible for less than a second, becoming obscured by terrain almost immediately.
.....and pages 29 and 30....
As noted in Section D-VII, non-precision approach procedures specify how the airplane is to descend on the final approach course to the Minimum Descent Altitude (MDA), which in this case is 1200 ft. MSL. To descend from the MDA, the crew must have the airport / runway environment in sight, and complete the descent and landing visually. However, the security video analysis described in Section D-VI indicates that the airplane was not below the clouds (and the runway would not have been visible from the cockpit) until about 1000 ft. MSL, 200 ft. below the MDA. This finding is consistent with the crew’s reporting the airport in sight at about 900 ft. MSL.
Furthermore, the PAPI visibility analysis described in Section D-VII indicates that when the crew reported the runway in sight at about 900 ft. MSL and about 1.24 nmi north of the threshold, the PAPI would have been visible for less than a second, becoming obscured by terrain almost immediately. Consequently, it is likely that the crew never saw or recognized the PAPI lights, which could have alerted them to the airplane’s dangerously low altitude.
aterpster:
Nonetheless sighting of the PAPIs was required before they departed MDA, which this crew apparently didn't understand.
Correct...... but I seriously doubt the NTSB will ever conclude that the crew didn't understand this. Nor that they didn't know they were supposed to sequence the FMC and "extend" the approach; nor that they didn't know that the autopilot was supposed to be disconnected by 50 ft below the MDA; nor that they didn't understand that 1500 fpm at 1000 ft afe is an unstable approach requiring a go around; nor that they thought the "minimums" and 500 ft callouts were optional. The question will be, what human factors caused them to make all these omissions?