Narrative:

As the pilot flying I was executing the localizer 4R GS OTS approach into bos. At approximately 660 ft MSL tower issued a low altitude alert. We were 220 ft above MDA descending at 1200 FPM within stabilized approach criteria approximately 4.9 miles from the threshold. We were below the reported ceiling of 2100' but visibility was closer to 4 miles rather than 10 miles that was reported by the ATIS due to rain on the approach. I did have ground contact but not the runway in sight. Due to the distraction of ATC I diverted my scan from the instruments. The autopilot failed to capture at 440 ft which was set in the altitude alert window. I looked back inside at the instruments and simultaneously the captain commanded I stop my descent. Now realizing the aircraft had descended through the MDA I disconnected the autopilot and pitched back up to MDA while adding power. At this point the GPWS alerted a too low terrain warning; although I now had the runway in sight. I rejoined the PAPI and executed a normal landing. I believe the event occurred due to distraction and the inherent shortcomings of a non-precision dive and drive approach; which can lead to erroneous low altitude alerts. I am also to blame for not monitoring the instruments more closely and failing to immediately notice the aircraft had descended through the altitude set in the alert window. I was startled to not see it capture. I also believe weather was a contributing factor and was actually better on the field than on the final approach. I will now arm profile on a non-precision approach when able; and even when in VMC will maintain a closer watch of the autoflight system and try not to fall into the trap of automation complacency.

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Original NASA ASRS Text

Title: Flight crew of a medium large transport aircraft receive both tower and aircraft generated low altitude alerts while flying a non-precision LOC APCH to Runway 4R at BOS.

Narrative: As the pilot flying I was executing the LOC 4R GS OTS approach into BOS. At approximately 660 FT MSL tower issued a low altitude alert. We were 220 FT above MDA descending at 1200 FPM within stabilized approach criteria approximately 4.9 miles from the threshold. We were below the reported ceiling of 2100' but visibility was closer to 4 miles rather than 10 miles that was reported by the ATIS due to rain on the approach. I did have ground contact but not the runway in sight. Due to the distraction of ATC I diverted my scan from the instruments. The autopilot failed to capture at 440 FT which was set in the altitude alert window. I looked back inside at the instruments and simultaneously the Captain commanded I stop my descent. Now realizing the aircraft had descended through the MDA I disconnected the autopilot and pitched back up to MDA while adding power. At this point the GPWS alerted a TOO LOW TERRAIN warning; although I now had the runway in sight. I rejoined the PAPI and executed a normal landing. I believe the event occurred due to distraction and the inherent shortcomings of a non-precision dive and drive approach; which can lead to erroneous low altitude alerts. I am also to blame for not monitoring the instruments more closely and failing to immediately notice the aircraft had descended through the altitude set in the alert window. I was startled to not see it capture. I also believe weather was a contributing factor and was actually better on the field than on the final approach. I will now arm profile on a non-precision approach when able; and even when in VMC will maintain a closer watch of the autoflight system and try not to fall into the trap of automation complacency.

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.