Narrative:

We were initially being vectored to the ILS xx approach; when the winds switched around; favoring runway yy. We were already on base leg for the ILS when we were told of the change and asked what approach we desired. The captain and I elected to be vectored to the RNAV yy approach. The controller vectored us onto the downwind leg; and the captain and I quickly reset the FMS for the RNAV yy. We transferred control; and I briefed the approach; indicating that I would use the prof mode down to the LNAV minimums of 440. We were prepared and configured prior to beginning the approach; and I did not feel rushed or concerned about the approach; although I knew that based on the ceilings being reported there was a good chance that we would not see the runway. Sure enough; we didn't see the runway. As the FMA indicated altitude hold; I executed a normal missed approach. We climbed back to 3;000 feet and were vectored out to the west of the airport. The controller asked what our intentions were; and the captain said that we'd like to go back toward the approach again and see if the other air carrier behind us got in. We jointly computed the amount of fuel we would need to reach our alternate; and determined that we had enough fuel for one more attempt at the approach. We briefed that if a missed approach was again necessary; we would immediately divert to our alternate. On left base for the approach; the controller told us that the other air carrier landed; and that he reported breaking out right at minimums. We elected to continue the approach. I stated that I was concerned that we still wouldn't make it in; since by our RNAV/prof procedures; we never actually make it down to minimums. The captain stated that he thought I was planning on doing the approach as a 'dive and drive.' I told him that I had used prof the first time; and questioned whether we could do an RNAV without prof. The captain stated that he was certain we could; so I agreed. (The fact that I'd never heard anyone mention RNAV approaches without prof should have been a red flag.) we were turned onto and cleared for the approach. I would have felt more comfortable breaking off the approach and completing an entire approach briefing; but that would have negated the approach attempt; since we were already near minimum fuel. Had we completed a new briefing; we would have noticed the intervening fix between the RNAV final approach fix and runway yy; with a crossing altitude of 540 feet. I configured on schedule and started down toward 440 feet; the LNAV MDA planning to level at MDA and drive to our planned vdp of 1.2 miles from the runway yy threshold. As we passed through 500 feet; we were issued a 'low altitude alert' by tower. It was only then that I remembered the intervening fix. Very soon thereafter we broke out; saw the runway; and landed normally. As I recall; we descended below the 540 foot crossing approximately half a mile outside the crossing waypoint. 1) the RNAV crossing waypoint is not in the approach database. There are quite a few approaches in the system that don't have all the fixes on an approach listed in the FMS database. Every approach fix; regardless of whether it is required for the approach or not; should be shown. Had we seen the crossing waypoint altitude constraint depicted on the FMS and navigation displays; I'm certain we would have both said 'hold on a minute...' before descending too far. 2) in the heat of the moment; the captain and I both failed to remember that RNAV approaches must be flown in prof; unless prof is unavailable for some technical reason. Even though I knew that a 'dive and drive' RNAV didn't sound right; the captain's certainty led me to believe that I was in error. I think part of the problem is that flight crews can be overwhelmed by the number of approach options available; especially when executing approaches that are seldom used; such as rnavs. Perhaps we could include a list of approachtypes and the approved approach techniques (prof vs. Dive and drive) and minima on the back of the checklist for easy review. 3) the RNAV setup checklist on the back of the checklist should be amended to say 'all RNAV approaches must be flown in prof; unless prof is unavailable;' and perhaps even 'VOR approaches may not be flown using prof.' these are huge limitations; and are addressed nowhere on the checklist. Again; for approaches that are rarely used; any extra guidance is helpful. 4) the aom only states that all rnavs should be flown in prof under the RNAV without prof procedure. That note should be duplicated in the RNAV with prof procedure.

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Original NASA ASRS Text

Title: A B717 crew completed an RNAV approach without the PROF (Profile) Mode engaged and descended below an intermediate waypoint constraint which was not in the FMC RNAV database for the selected runway. ATC issued a low altitude alert.

Narrative: We were initially being vectored to the ILS XX approach; when the winds switched around; favoring Runway YY. We were already on base leg for the ILS when we were told of the change and asked what approach we desired. The Captain and I elected to be vectored to the RNAV YY approach. The controller vectored us onto the downwind leg; and the Captain and I quickly reset the FMS for the RNAV YY. We transferred control; and I briefed the approach; indicating that I would use the PROF mode down to the LNAV minimums of 440. We were prepared and configured prior to beginning the approach; and I did not feel rushed or concerned about the approach; although I knew that based on the ceilings being reported there was a good chance that we would not see the runway. Sure enough; we didn't see the runway. As the FMA indicated ALT HOLD; I executed a normal missed approach. We climbed back to 3;000 feet and were vectored out to the west of the airport. The Controller asked what our intentions were; and the Captain said that we'd like to go back toward the approach again and see if the other air carrier behind us got in. We jointly computed the amount of fuel we would need to reach our alternate; and determined that we had enough fuel for one more attempt at the approach. We briefed that if a missed approach was again necessary; we would immediately divert to our alternate. On left base for the approach; the controller told us that the other air carrier landed; and that he reported breaking out right at minimums. We elected to continue the approach. I stated that I was concerned that we still wouldn't make it in; since by our RNAV/PROF procedures; we never actually make it down to minimums. The Captain stated that he thought I was planning on doing the approach as a 'dive and drive.' I told him that I had used PROF the first time; and questioned whether we could do an RNAV without PROF. The Captain stated that he was certain we could; so I agreed. (The fact that I'd never heard anyone mention RNAV approaches without PROF should have been a red flag.) We were turned onto and cleared for the approach. I would have felt more comfortable breaking off the approach and completing an entire approach briefing; but that would have negated the approach attempt; since we were already near minimum fuel. Had we completed a new briefing; we would have noticed the intervening fix between the RNAV final approach fix and Runway YY; with a crossing altitude of 540 feet. I configured on schedule and started down toward 440 feet; the LNAV MDA planning to level at MDA and drive to our planned VDP of 1.2 miles from the Runway YY threshold. As we passed through 500 feet; we were issued a 'low altitude alert' by Tower. It was only then that I remembered the intervening fix. Very soon thereafter we broke out; saw the runway; and landed normally. As I recall; we descended below the 540 foot crossing approximately half a mile outside the crossing waypoint. 1) The RNAV crossing waypoint is not in the approach database. There are quite a few approaches in the system that don't have all the fixes on an approach listed in the FMS database. Every approach fix; regardless of whether it is required for the approach or not; should be shown. Had we seen the crossing waypoint altitude constraint depicted on the FMS and NAV displays; I'm certain we would have both said 'hold on a minute...' before descending too far. 2) In the heat of the moment; the Captain and I both failed to remember that RNAV approaches must be flown in PROF; unless PROF is unavailable for some technical reason. Even though I knew that a 'dive and drive' RNAV didn't sound right; the Captain's certainty led me to believe that I was in error. I think part of the problem is that flight crews can be overwhelmed by the number of approach options available; especially when executing approaches that are seldom used; such as RNAVs. Perhaps we could include a list of approachtypes and the approved approach techniques (PROF vs. dive and drive) and minima on the back of the checklist for easy review. 3) The RNAV setup checklist on the back of the checklist should be amended to say 'All RNAV approaches must be flown in PROF; unless PROF is unavailable;' and perhaps even 'VOR approaches may not be flown using PROF.' These are huge limitations; and are addressed nowhere on the checklist. Again; for approaches that are rarely used; any extra guidance is helpful. 4) The AOM only states that all RNAVs should be flown in PROF under the RNAV Without PROF procedure. That note should be duplicated in the RNAV with PROF procedure.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.