Narrative:

Aus was operating under cenrap+ (cenrap plus) conditions due to aus secondary radar being out of service. Cenrap+ uses secondary radar feeds from ZHU ARTCC and sat approach control; and overlays this information on top of aus primary radar. This system presents a significant lag in data-tag updates on the BRITE radar display in the tower; data-tags drop from every primary target when the aircraft is within 10 miles from the airport; primary 'trails' can not be enhanced to assist with primary history; tower is responsible for manually track-starting departure tags or providing the TRACON with a rolling report; and the 'last to land lists' are not updated. I wrote aircraft X on the right column of my pad at the local control position; indicating that this aircraft was inbound to runway 35R. The aircraft checked-in on my frequency and I cleared him to land; but I neglected to place a check-mark next to the call sign; indicating that I had issued a landing clearance. Aircraft Y called ready for departure. I picked-up aircraft Y's flight progress strip... Looked at the BRITE for data tags or traffic... Scanned the runway for traffic... Scanned the departure path for traffic... And then looked at my pad. I saw aircraft X unchecked on the pad; but this did not register with me; and I issued aircraft Y a take-off clearance and then went to perform other tasks. Aircraft Y told me that he saw traffic on final. I looked out the window and saw an aircraft dipping below the tree line; and I think that I canceled the takeoff clearance... Or told aircraft Y to hold short. I then realized that I had forgotten about aircraft X. An accident or incident might have occurred if aircraft Y had not seen the landing traffic. I do not believe that aircraft X heard me issue aircraft Y a departure clearance; as the pilot did not say anything; and the aircraft did not initiate a go-around. Aircraft Y never crossed the runway hold-short line. Recommendation; working local control under cenrap+ was labor intensive; and all of my focus was trained on the BRITE radar display to ensure that all departures were tagging-up prior to issuing a frequency change. I should have slowed-down a bit to ensure that nothing was missed. This was a classic example of looking; but not 'seeing'. In meetings; I have repeatedly asked for a front line manager (flm) to be assigned to the tower; or that a dedicated controller-in-charge (controller in charge) be assigned to the tower and assigned to the cab coordinator position. If there had been an extra set of eyes in the tower; this situation might have been prevented. Due to the haze and the color of aircraft Y; I was unable to see the aircraft until it was below the tree-line. Maybe I should scan the horizon with binoculars; but this would be rather labor intensive. The shades were down; and my visibility might have been better if the shades were up.

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Original NASA ASRS Text

Title: AUS Local Controller described near loss of separation event when clearing an aircraft for takeoff with traffic on short final; reporter listed use of CENRAP as a causal factor.

Narrative: AUS was operating under CENRAP+ (Cenrap Plus) conditions due to AUS Secondary RADAR being out of service. CENRAP+ uses secondary RADAR feeds from ZHU ARTCC and SAT Approach Control; and overlays this information on top of AUS primary RADAR. This system presents a significant lag in data-tag updates on the BRITE RADAR display in the Tower; data-tags drop from every primary target when the aircraft is within 10 miles from the airport; primary 'trails' can not be enhanced to assist with primary history; Tower is responsible for manually track-starting departure tags or providing the TRACON with a rolling report; and the 'last to land lists' are not updated. I wrote Aircraft X on the right column of my pad at the Local Control position; indicating that this aircraft was inbound to Runway 35R. The aircraft checked-in on my frequency and I cleared him to land; but I neglected to place a check-mark next to the call sign; indicating that I had issued a landing clearance. Aircraft Y called ready for departure. I picked-up Aircraft Y's flight progress strip... looked at the BRITE for data tags or traffic... scanned the runway for traffic... scanned the departure path for traffic... and then looked at my pad. I saw Aircraft X unchecked on the pad; but this did not register with me; and I issued Aircraft Y a take-off clearance and then went to perform other tasks. Aircraft Y told me that he saw traffic on final. I looked out the window and saw an aircraft dipping below the tree line; and I think that I canceled the takeoff clearance... or told Aircraft Y to hold short. I then realized that I had forgotten about Aircraft X. An accident or incident might have occurred if Aircraft Y had not seen the landing traffic. I do not believe that Aircraft X heard me issue Aircraft Y a departure clearance; as the pilot did not say anything; and the aircraft did not initiate a go-around. Aircraft Y never crossed the runway hold-short line. Recommendation; working Local Control under CENRAP+ was labor intensive; and all of my focus was trained on the BRITE RADAR display to ensure that all departures were tagging-up prior to issuing a frequency change. I should have slowed-down a bit to ensure that nothing was missed. This was a classic example of looking; but not 'seeing'. In meetings; I have repeatedly asked for a Front Line Manager (FLM) to be assigned to the Tower; or that a dedicated Controller-In-Charge (CIC) be assigned to the Tower and assigned to the Cab Coordinator position. If there had been an extra set of eyes in the Tower; this situation might have been prevented. Due to the haze and the color of Aircraft Y; I was unable to see the aircraft until it was below the tree-line. Maybe I should scan the horizon with binoculars; but this would be rather labor intensive. The shades were down; and my visibility might have been better if the shades were up.

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.