Flight crew reported conflicting glidepath information while on a RNAV GPS approach to Runway 20 at CMD in visual conditions. The flight crew received a RAAS 'too high' callout; while the aircraft was on the RNAV GPS glidepath; and the ground PAPI guidance was showing the aircraft high. The aircraft landed in the touchdown zone.
Synopsis
Flight crew reported conflicting glidepath information while on a RNAV GPS approach to Runway 20 at CMD in visual conditions. The flight crew received a RAAS 'too high' callout; while the aircraft was on the RNAV GPS glidepath; and the ground PAPI guidance was showing the aircraft high. The aircraft landed in the touchdown zone.
Narrative
While conducting a visual approach to Runway 20 (backed up by the RNAV (GPS) 20 approach) we got a too high; too high" RAAS (Runway Awareness and Advisory System) annunciation. We were more than 500 ft above TDZE; and we did not appear high visually. Descent rate was not excessive and airspeed was appropriate. (Discussing the event after the flight; we both agreed we were less than 1/2 dot high on the glide path.) We discussed whether a go around was necessary. Neither of us thought we were high; and we were within stabilized approach criteria. However; the PAPI indicated we were high. We decided to continue the approach to a landing. We never intercepted the PAPI glide path; and the flying pilot stopped trying to capture it. At 500 ft above TDZE the approach was stable--we were on the approach glide path--though the PAPI still indicated we were high. Afterwards we agreed the PAPI was not providing accurate information. Of note; on the recorded ASOS the PAPI for Runway 2 was mentioned as inoperative though there was no published NOTAM.If the PAPI for Runway 2 is inoperative a NOTAM should be published. I think the PAPI for Runway 20 should be checked. Otherwise; I am at a loss as to how two separate systems would indicate similar conditions (that we were high) while other aircraft systems and the crew did not indicate/perceive the same conditions."
Second reporter narrative
While on a visual approach to Runway 20 at CMD we received an eGPWS (Enhanced Ground Proximity Warning System) Too High" call; this was the only callout from the system. This was prior to the 500 foot stabilized call. I thought I was slowing appropriately and that I was on the RNAV glide path for the runway. At 500 feet; my FO called "500; stable"; I responded "landing". We both thought our approach angle was appropriate. While on short final; still over the trees; prior to the clear zone; the PAPI showed that we high; but that I felt certain that was wrong. I felt that descending to a shallower approach angle would have but us too unsafely close to the trees and I also felt very confidant that we were on a 3.0° angle. In short; I did not believe the PAPI. We landed in the touchdown zone and stopped with moderate brake and reverse thrust with approximately 2;000 ft of runway remaining. We discussed the approach thoroughly after the passenger departed. Neither of us thought we were unstable or in a position that required a good-around. Both of thought a safe landing was possible and that we did indeed make a safe and legal landing. We were both surprised and confused by the "too high" call and the especially the PAPI. At debrief; I think that both of us disbelieved the PAPI. I also think I was on the electronic glide path. The only other issue I think could have caused me to think we on the correct glide path is the downslope runway illusion. This runway did slope down in the direction we were landing and this could very well have caused my thought that we were okay when we in fact high. I think in the future I need to pay more attention to runway slope during my approach briefings. I also should have performed a missed approach when equipment that is not known to be malfunctioning is telling me I'm high. There may be a disconnect between the RNAV glide slope and the PAPI. A second attempt at the approach using the visual approach function of the FMS would have been helpful to verify a correct approach angle. I need to trust the equipment as I'm gaining experience in a new aircraft (I'm still low-time and high mins)."
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.