Narrative:

Working cab radar approach control; I took a hand off on air carrier X 10 miles southeast of my southeast border. I believe air carrier X was already level at 8;000 ft; which is his lowest descent altitude per our LOA. In general; these aircraft come over much higher; sometimes still descending from flight levels. On my flight strip; I had preplanned air carrier X to descend to 4;000 ft for sequence with a C750 inbound from the south; who I was going to have descending to 3;000 ft. When air carrier X checked on; I gave him direct outer marker for a visual [approach] and a pilot discretionary descent to 3;000 ft. The pilot read this back correctly and I mistakenly gave him the incorrect altitude by getting ahead of myself. The C750 checked on and I descended him as well to 3;000 ft; not realizing that is what I had just issued to air carrier X. Air carrier X then reported he was vacating 8;000 ft; but did not say to what altitude. Completely confident I had just issued air carrier X 4;000 ft; I did not pass terrain obstruction information for an antenna 15 miles at his twelve [o'clock position]. The MVA for this obstruction is 3;600 ft. This mistake had not been realized until the MSAW alert went off. The alert did not trigger until air carrier X was crossing just south of the antenna at 3;100 ft. By the time I had realized air carrier X's proximity to the antenna he was already past the obstruction at 3;000 ft. I asked the pilot to verify level at 4;000 ft and he read back 3;000 ft. I had air carrier X remain at 3;000 ft as this was the MVA from that point on. When I checked the tapes; I did in fact issue 3;000 ft. A few contributing factors to this scenario may have been the low volume of traffic and simple human error. All read back/hear back was correct; I just committed a simple mistake. This antenna is at our outermost southeast boundary and is very rarely a factor. Also; air carrier X's unusually low altitude for his distance from the airport and his decision to descend at a higher rate than normal may also have contributed to this unsafe proximity. As far as I am aware; the pilot committed no error. I just simply had not realized I issued the wrong intended altitude. My only recommendations are to myself. I must remain more vigilant and focused during low traffic periods. I do habitually use safe initial altitudes corresponding with direction of flight and other aircraft. This is why I preplanned my altitude at 4;000 ft heading westbound with traffic to pass beneath at 3;000 ft; closer to the airport. I realize now that if I pre-plan my altitude I must either use a different color pen or some trigger to have myself double check as the altitude is being issued to the pilot. Also; I must be more aware of the pilot read back to possibly help catch my own mistakes. The one external recommendation that may have helped me catch my error would be to have the MSAW trigger much sooner than it did. By the time it alarmed the event was concluding itself.

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Original NASA ASRS Text

Title: Approach Controller described an MVA infraction when issuing an altitude below published standards; resulting in an MSAW alert.

Narrative: Working Cab RADAR Approach Control; I took a hand off on Air Carrier X 10 miles SE of my SE border. I believe Air Carrier X was already level at 8;000 FT; which is his lowest descent altitude per our LOA. In general; these aircraft come over much higher; sometimes still descending from flight levels. On my flight strip; I had preplanned Air Carrier X to descend to 4;000 FT for sequence with a C750 inbound from the south; who I was going to have descending to 3;000 FT. When Air Carrier X checked on; I gave him direct outer marker for a visual [approach] and a pilot discretionary descent to 3;000 FT. The pilot read this back correctly and I mistakenly gave him the incorrect altitude by getting ahead of myself. The C750 checked on and I descended him as well to 3;000 FT; not realizing that is what I had just issued to Air Carrier X. Air Carrier X then reported he was vacating 8;000 FT; but did not say to what altitude. Completely confident I had just issued Air Carrier X 4;000 FT; I did not pass terrain obstruction information for an antenna 15 miles at his twelve [o'clock position]. The MVA for this obstruction is 3;600 FT. This mistake had not been realized until the MSAW alert went off. The alert did not trigger until Air Carrier X was crossing just south of the antenna at 3;100 FT. By the time I had realized Air Carrier X's proximity to the antenna he was already past the obstruction at 3;000 FT. I asked the pilot to verify level at 4;000 FT and he read back 3;000 FT. I had Air Carrier X remain at 3;000 FT as this was the MVA from that point on. When I checked the tapes; I did in fact issue 3;000 FT. A few contributing factors to this scenario may have been the low volume of traffic and simple human error. All read back/hear back was correct; I just committed a simple mistake. This antenna is at our outermost SE boundary and is very rarely a factor. Also; Air Carrier X's unusually low altitude for his distance from the airport and his decision to descend at a higher rate than normal may also have contributed to this unsafe proximity. As far as I am aware; the pilot committed no error. I just simply had not realized I issued the wrong intended altitude. My only recommendations are to myself. I must remain more vigilant and focused during low traffic periods. I do habitually use safe initial altitudes corresponding with direction of flight and other aircraft. This is why I preplanned my altitude at 4;000 FT heading westbound with traffic to pass beneath at 3;000 FT; closer to the airport. I realize now that if I pre-plan my altitude I must either use a different color pen or some trigger to have myself double check as the altitude is being issued to the pilot. Also; I must be more aware of the pilot read back to possibly help catch my own mistakes. The one external recommendation that may have helped me catch my error would be to have the MSAW trigger much sooner than it did. By the time it alarmed the event was concluding itself.

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.