Narrative:

I was working the log while local control 1 was issuing a 'low approach only' instruction to aircraft Y on short final. Aircraft X called from runway 25R north side run-up area requesting right closed traffic; however; because the pilot over-keyed the local control controller; the beginning of the transmission (call sign and position) was clipped. Local control 1; realizing that his transmission may have been blocked; restated his instructions to aircraft Y. Aircraft X then stated 'right closed traffic RWY25R; aircraft X'. I saw aircraft X move forward; however; I did not recognize that he was passing the hold short lines. I did watch to make sure the aircraft came to a complete stop; which it did; still clear of the runway; just before aircraft Y crossed the threshold. While there was no time to have sent aircraft Y around; I should have recognized that aircraft X was passing the hold short lines as I watched it move forward. It wasn't until aircraft X asked for verification that he was cleared for [runway] 25R and other controllers stated that he had crossed the lines that I realized this was the case.because of the low height of our tower; it's difficult for us to see our hold short lines. The lines are also closer to the runway on the north side than they are on the south side. I've been at this facility for several years now however; so I'm used to this being an issue and have caught mistakes like this before. Traffic volume was very heavy and there was some complexity due to the fact that we were split; training on local control 2 and a relief briefing had just occurred on ground control. I may have been trying to multi-task too much; dividing my attention between local control 1; local control 2 and ground control; rather than giving each of them all my attention at different times. I will be more careful in the future to give all my attention to one position at a time.

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Original NASA ASRS Text

Title: Livermore Tower Controller reported a runway incursion.

Narrative: I was working the log while Local Control 1 was issuing a 'low approach only' instruction to Aircraft Y on short final. Aircraft X called from RWY 25R north side run-up area requesting right closed traffic; however; because the pilot over-keyed the Local Control Controller; the beginning of the transmission (call sign and position) was clipped. Local Control 1; realizing that his transmission may have been blocked; restated his instructions to Aircraft Y. Aircraft X then stated 'Right closed traffic RWY25R; Aircraft X'. I saw Aircraft X move forward; however; I did not recognize that he was passing the hold short lines. I did watch to make sure the aircraft came to a complete stop; which it did; still clear of the runway; just before Aircraft Y crossed the threshold. While there was no time to have sent Aircraft Y around; I should have recognized that Aircraft X was passing the hold short lines as I watched it move forward. It wasn't until Aircraft X asked for verification that he was cleared for [Runway] 25R and other controllers stated that he had crossed the lines that I realized this was the case.Because of the low height of our Tower; it's difficult for us to see our hold short lines. The lines are also closer to the runway on the north side than they are on the south side. I've been at this facility for several years now however; so I'm used to this being an issue and have caught mistakes like this before. Traffic volume was very heavy and there was some complexity due to the fact that we were split; training on Local Control 2 and a relief briefing had just occurred on Ground Control. I may have been trying to multi-task too much; dividing my attention between Local Control 1; Local Control 2 and Ground Control; rather than giving each of them all my attention at different times. I will be more careful in the future to give all my attention to one position at a time.

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.