Approach controller descended cpr X below MVA while on a radar surveillance approach. System error.

Attributes
ACN	184838
Time
Date	199107
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : sat
State Reference	TX
Altitude	msl bound lower : 1200 msl bound upper : 2600
Environment
Flight Conditions	Marginal
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : sat
Operator	general aviation : corporate
Make Model Name	Light Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent : approach descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller non radar : 9 controller radar : 5
ASRS Report	184838
Person 2
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	non adherence : published procedure other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	faa : investigated
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I was vectoring the aircraft for a surveillance approach to a secondary runway (at pilots request). Since I am a staff specialist it had been some time since I had done a surveillance approach. At approximately 10 mi from the airport after receiving descent clearance to 3000, the pilot asked if he could continue down to 1200 (the min descent altitude). I wrongly approved the request and the aircraft crossed the 5 mi mark level at 1200 (the MVA is 2600). The pilot indicated that when he broke out of the clouds he was in proximity to some antennas that appeared to be at his altitude. The height of the antennas is believed to be 1349 ft. Causal factors: controller (myself) not proficient. I read the wrong MDA off the display in TRACON. Correct MDA is 1280 to 1200. Although volume of traffic was not heavy I had 2 distrs (an aircraft with no transponder, decombining radar positions) which diverted my attention. After I issued incorrect altitude, the data block (track) went into coast.

Original NASA ASRS Text

Title: APCH CTLR DSNDED CPR X BELOW MVA WHILE ON A RADAR SURVEILLANCE APCH. SYS ERROR.

Narrative: I WAS VECTORING THE ACFT FOR A SURVEILLANCE APCH TO A SECONDARY RWY (AT PLTS REQUEST). SINCE I AM A STAFF SPECIALIST IT HAD BEEN SOME TIME SINCE I HAD DONE A SURVEILLANCE APCH. AT APPROX 10 MI FROM THE ARPT AFTER RECEIVING DSCNT CLRNC TO 3000, THE PLT ASKED IF HE COULD CONTINUE DOWN TO 1200 (THE MIN DSCNT ALT). I WRONGLY APPROVED THE REQUEST AND THE ACFT CROSSED THE 5 MI MARK LEVEL AT 1200 (THE MVA IS 2600). THE PLT INDICATED THAT WHEN HE BROKE OUT OF THE CLOUDS HE WAS IN PROXIMITY TO SOME ANTENNAS THAT APPEARED TO BE AT HIS ALT. THE HEIGHT OF THE ANTENNAS IS BELIEVED TO BE 1349 FT. CAUSAL FACTORS: CTLR (MYSELF) NOT PROFICIENT. I READ THE WRONG MDA OFF THE DISPLAY IN TRACON. CORRECT MDA IS 1280 TO 1200. ALTHOUGH VOLUME OF TFC WAS NOT HVY I HAD 2 DISTRS (AN ACFT WITH NO TRANSPONDER, DECOMBINING RADAR POSITIONS) WHICH DIVERTED MY ATTN. AFTER I ISSUED INCORRECT ALT, THE DATA BLOCK (TRACK) WENT INTO COAST.

Data retrieved from NASA's ASRS site as of July 2007 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.