Narrative:

I was the pilot flying on our last leg to ZZZZ. We were cleared the RNAV approach. I fully briefed the approach; and emphasized the need to not edit the approach while in prof because [the FMS] would not [then] adhere to [published] altitude limits. We were on the published approach and were then cleared direct to zzzzz [the FAF]. Prior to this we had put min prof [da(H) altitude] in the altitude alert window since we were cleared the approach. We were coming in to zzzzz at a 25 degree angle or so and; at about 2-3 miles from zzzzz; we were descending through 3;000 which was the altitude [crossing] restriction for this fix. I was a bit confused in that I was now thinking that we were descending because we were on the predicted [glide] path; much like when you capture the glideslope [but] are still waiting for localizer capture. It became obvious very soon that we were actually descending because the FMS [mode] had been changed to direct and the altitude at zzzzz was being disregarded. I intervened with vertical speed up to recapture the path and get back up to 3;000. At this same time tower called and said we were showing low on the approach and the captain [responded that we were] correcting. We were approximately 2;450 or so MSL at the lowest based on my recollection. The captain wanted me to limit my V speed up because he was concerned about noise; I was more concerned with getting back to a safe altitude at this point. We intercepted the path and flew a stabilized approach to a normal touchdown.

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Original NASA ASRS Text

Title: An MD-11 flight crew cleared to fly an RNAV approach mistakenly modified the line selectable procedure when cleared direct from their transition route to the FAF. When doing so the crossing restriction at the FAF was deleted and the aircraft descended directly toward the DA(H). A low altitude alert was transmitted by the Tower and the flight returned to their clearance and completed the approach and landing.

Narrative: I was the pilot flying on our last leg to ZZZZ. We were cleared the RNAV approach. I fully briefed the approach; and emphasized the need to not edit the approach while in PROF because [the FMS] would not [then] adhere to [published] ALT limits. We were on the published approach and were then cleared direct to ZZZZZ [the FAF]. Prior to this we had put min Prof [DA(H) altitude] in the altitude alert window since we were cleared the approach. We were coming in to ZZZZZ at a 25 degree angle or so and; at about 2-3 miles from ZZZZZ; we were descending through 3;000 which was the ALT [crossing] restriction for this fix. I was a bit confused in that I was now thinking that we were descending because we were on the predicted [glide] path; much like when you capture the glideslope [but] are still waiting for LOC capture. It became obvious very soon that we were actually descending because the FMS [mode] had been changed to direct and the ALT at ZZZZZ was being disregarded. I intervened with vertical speed up to recapture the path and get back up to 3;000. At this same time tower called and said we were showing low on the approach and the Captain [responded that we were] correcting. We were approximately 2;450 or so MSL at the lowest based on my recollection. The Captain wanted me to limit my V speed up because he was concerned about noise; I was more concerned with getting back to a safe altitude at this point. We intercepted the path and flew a stabilized approach to a normal touchdown.

Data retrieved from NASA's ASRS site as of July 2013 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.