A crew flew the VGC RNAV Z Runway 17 LPV approach; descended below the vertical path and received a terrain warning because they did not realize the approach was not a RNAV GPS LNAV approach.
Synopsis
A crew flew the VGC RNAV Z Runway 17 LPV approach; descended below the vertical path and received a terrain warning because they did not realize the approach was not a RNAV GPS LNAV approach.
Narrative
My Captain and I were scheduled to fly to VGC. The preparation for this ferry flight was a little more detailed than most. Both of us were unfamiliar with VGC and spent some time reviewing the charts and climb performance before we left. One of our main concerns was the length of the runway being only 5;300 FT in VGC and the fact that performance would be tight for the subsequent takeoff on our second leg of the trip. We also knew that the weather was marginal for landing and we would need the lowest approach available considering the winds. We received our clearance; taxied out and determined that the entire flight would be IFR. Some discussion was made between the two of us that Runway 17 would be in use at VGC. The en-route portion of our trip was relatively short and busy trying to get the updated weather; and setting up for the approach. Again we both thought that Runway 17 was our best bet and we wanted the lowest approach available. We were queried by the Controller what approach we wanted to shoot; and we stated we wanted the RNAV Z 17; He queried us if we did not mean the RNAV Y approach to 35; but when we restated our request; he cleared us for the RNAV GPS Z Runway 17 approach. We had already set up and briefed this RNAV GPS Z Runway 17 approach. While reviewing the chart I failed to realize or state that this approach was an RNAV GPS LPV approach and not the normal RNAV GPS LNAV. Evidently the Captain also missed this fact. We flew the approach as if it were LNAV only; using the fixes on the chart and the minimums listed. The ceiling at the time was 1;100 overcast and good visibility; so we broke out nearly 4 miles from the field and were in visual conditions. It was at this point that we received a GPWS warning of 'terrain; terrain'; that led to a pull up warning. Both the Captain and I confirmed that we were in good visual conditions having both the airport and all terrain in sight. We continued with the approach and landed safely on Runway 17. A discussion between the crew and the Assistant Chief Pilot (ACP) on duty later that evening revealed our mistake. We had mistakenly shot the RNAV GPS Z LPV approach to Runway 17 instead of the GPS RNAV Y approach to Runway 35. I feel there were several things that led to this error. First; I personally was concerned about the performance issues for the next leg and spent too much time worried about whether we would meet it or not. I should have given a more detailed look at the approach chart during the briefing and realized that there was no final approach fix for this approach; or LNAV only minimums. We had talked about Runway 17 as the favored runway several times and this led to its selection as the best option for our approach. (It was the only approach for that runway). The days preceding this trip were filled with multiple delays; storms and bad weather leading to the possibility of some fatigue; though I did not feel particularly fatigued at the time of this trip. From now on; I will be sure that there is a final approach fix (X) listed and published on the chart; and insure that there are LNAV minimums for the approach with step downs listed. We also should have questioned our actions when the controller questioned our initial intentions. I also think that a different NAME or Wording for the RNAV GPS LPV approach identification could be used to accentuate the difference of this approach from its LNAV counterpart. (Example being RNAV GLIDESLOPE ONLY). By both charts having the same beginning title as RNAV GPS leads to confusion. More diligence on our part should have prompted us to review it again.
Second reporter narrative
Once on the ground; we thought something was erroneous with either the software or the GPWS system. I called Dispatch to have them notify the appropriate departments. It wasn't until that evening when the Assistant Chief Pilot called and left me a message wanting the details of the approach did I discover our error. I called Dispatch and had them email me the approach plate. Once I reviewed it; it was clear as day; the mistake was ours. Both of us missed the minimums stating LPV. I believe this oversight on our part could have been avoided if we would have taken the time to do a full approach brief. As mentioned earlier; it was a short flight with a high task load due to the weather and airspace; to an unfamiliar airport. I should have thoroughly reviewed all of the approaches available to us prior to commencing the approach.
NASA callback
The reporter stated that because of the weather the crew was determined to fly a south landing approach. They became confused because the short flight segment they had flown did not allow them time to re brief the approach and see that it was an LPV with vertical guidance. They set the approach up as an LNAV/VNAV; selected the minimum LPV DA 325 FT in the altitude set window and after the Final Approach Fix descended to that altitude which put them below the theoretical glide path resulting in a TERRAIN alert. The Reporter also commented that the chart titles RNAV (GPS) Y; RNAV (GPS) Z; and so on; are not descriptive enough to allow some preview alerting the crew to expect various type(s) of RNAV GPS approaches on that chart.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.