Gtf TRACON controller describes where he descended an aircraft below the MVA while working under cen...

Attributes
ACN	1202387
Time
Date	201409
Local Time Of Day	1201-1800
Place
Locale Reference	GTF.Airport
State Reference	MT
Environment
Light	Daylight
Aircraft 1
Make Model Name	Medium Large Transport
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Approach
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (mon) 7
Events
Anomaly	ATC Issue All Types Airspace Violation All Types Deviation - Procedural Published Material / Policy Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT

Narrative:

Aircraft X was inbound to gtf from the south. We were in cenrap; and I had the appropriate cenrap map selected. I descended aircraft X to 6000 ft in an 8500 ft MVA (that is 6000 ft in normal operations). This occurred approximately 19 miles from the airport. 12 miles from the airport; the aircraft reported the field in sight; and I cleared them for the visual approach. I do not know the altitude the aircraft was at when I cleared them; but a minute or two later; the local controller noticed aircraft X indicated 7000 ft on their mode C; which could not be validated due to cenrap. It was then I realized I had issued the descent to 6000 ft in the 8500 ft MVA.improved radar to maintain standard operations at all times. Also; MVA's that do not contradict one another based on cenrap or standard operations.

Original NASA ASRS Text

Title: GTF TRACON Controller describes where he descended an aircraft below the MVA while working under CENRAP conditions. Under normal radar conditions he would have been alright with the altitude descent.

Narrative: Aircraft X was inbound to GTF from the south. We were in CENRAP; and I had the appropriate CENRAP map selected. I descended Aircraft X to 6000 ft in an 8500 ft MVA (that is 6000 ft in normal operations). This occurred approximately 19 miles from the airport. 12 miles from the airport; the aircraft reported the field in sight; and I cleared them for the Visual Approach. I do not know the altitude the aircraft was at when I cleared them; but a minute or two later; the local controller noticed Aircraft X indicated 7000 ft on their Mode C; which could not be validated due to CENRAP. It was then I realized I had issued the descent to 6000 ft in the 8500 ft MVA.Improved radar to maintain standard operations at all times. Also; MVA's that do not contradict one another based on CENRAP or standard operations.

Data retrieved from NASA's ASRS site 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.

Gtf TRACON controller describes where he descended an aircraft below the MVA while working under cenrap conditions. Under normal radar conditions he would have been alright with the altitude descent.