A tower controller reported forgetting that a sweeper vehicle on the runway and cleared an aircraft ...

Narrative:

I cleared an aircraft to land on runway 28L on initial call near the final approach fix. Seeing my memory aid; I remembered there was an airport sweeper on the runway; which was approaching a taxiway turnoff. A helicopter called up for departure requesting a SVFR clearance. After communication with the helicopter was finished; I forgot to instruct the sweeper to exit the runway and instead tried to gain visual on the aircraft on approach. The aircraft was in IMC approaching decision height to be ready for missed approach instructions. When I saw the COL4 break out of the fog layer I then did a routine scan of the runway and my pad area. The memory aid was still in place over my pad and I then realized that I didn't give the sweeper instructions to exit the runway. At the same time recognizing the situation; the pilot initiated the go around.I should not clear an aircraft to land when there is a vehicle on the runway. The number one priority was to exit the sweeper before talking to another aircraft that was making an initial request from the ground.

Original NASA ASRS Text

Title: A Tower controller reported forgetting that a sweeper vehicle on the runway and cleared an aircraft to land. The aircraft on short final observed the sweeper and initiated a go around.

Narrative: I cleared an aircraft to land on Runway 28L on initial call near the final approach fix. Seeing my memory aid; I remembered there was an airport sweeper on the runway; which was approaching a taxiway turnoff. A helicopter called up for departure requesting a SVFR clearance. After communication with the Helicopter was finished; I forgot to instruct the sweeper to exit the runway and instead tried to gain visual on the aircraft on approach. The aircraft was in IMC approaching decision height to be ready for missed approach instructions. When I saw the COL4 break out of the fog layer I then did a routine scan of the runway and my pad area. The memory aid was still in place over my pad and I then realized that I didn't give the sweeper instructions to exit the runway. At the same time recognizing the situation; the pilot initiated the go around.I should not clear an aircraft to land when there is a vehicle on the runway. The number one priority was to exit the sweeper before talking to another aircraft that was making an initial request from the ground.

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.

Attributes
ACN	1387602
Time
Date	201609
Local Time Of Day	1201-1800
Place
Locale Reference	HWD.Airport
State Reference	CA
Environment
Flight Conditions	Marginal
Light	Daylight
Aircraft 1
Make Model Name	Cessna 400
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Flight Plan	IFR
Person 1
Function	Local
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 5.0
Person 2
Function	Ground
Qualification	Air Traffic Control Developmental
Events
Anomaly	ATC Issue All Types Conflict Ground Conflict Less Severe

A tower controller reported forgetting that a sweeper vehicle on the runway and cleared an aircraft to land. The aircraft on short final observed the sweeper and initiated a go around.