MB Re no PAPI indicated on the chart. I decode the “P/3.1” in the runway box, right hand column – Visual Slope, as indicating that PAPI is installed on runway 35 with an approach slope of 3.1 deg. In addition, I assume that the ‘non standard’ 3.1 deg is due to an alignment with the ILS, which previous posts indicted was above 3 deg due to distant obstacles.
Your observations and experience on-site are interesting, particularly as there is no information on the chart for crews. Is your experience with a ‘long body’ aircraft (MD11?) where a single PAPI installation may appear to be non-aligned with the ILS?
Other possibilities are that the specific PAPI installation uses a ‘tight’ beam setting and thus is very susceptible to aircraft size/configuration, or as intimated previously, less than ideal ILS GS accuracy well below DH.
The displaced ILS threshold is an interesting compromise particularly in a location where runway length is a premium. A possible alternative would have been to use an even higher GS angle ~ 3.3 deg to regain landing distance. Even at the high altitude, the steeper slope should not create any landing problems, furthermore the steeper angle would provide more precision and thus less scatter in the touchdown point; whereas the duck under / shallow approach does not.
I do not think that you should automatically assume that aiming to land short of the ILS threshold prohibits an ILS. Special techniques can be authorised for ‘difficult’ runways (post #96), but in these instances there are usually limitations or briefings to cover any additional risk. At Quito, I would expect the authority (Spain) / operator to consider the risks of deviating from the ILS approach (unstabilized), and even though this is to acquire a ‘stable’ visual approach, the speed / energy / time aspects of the higher altitude might move this to an unacceptable high risk operation. Also, - particularly; consider the effect of any tailwind.
I would expect higher ILS minima to aid the visual transition, and probably a tailwind restriction.
Ref:
“Safety aspects of tailwind operations”, (2001). Also see “Running out of runway” (2005).