Date: 201601
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Small Aircraft
Operator: Personal
Operating under: Part 91
Flight plan: VFR
Mission: Personal
Flight phase: Taxi
ATC / advisory: Tower ZZZ
Reporter organization: Government
Reporter function: Ground; Supervisor / CIC
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Human-Machine Interface; Confusion; Communication Breakdown; Situational Awareness; Workload
Anomaly: ATC Issue All Types; Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Detector: Person Air Traffic Control
When detected: Taxi; In-flight
Result: Air Traffic Control Separated Traffic; Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: ATC Equipment / Nav Facility / Buildings; Procedure; Environment - Non Weather Related; Airport; Aircraft
Primary problem: Aircraft

Narrative: I am a Front Line manager and was in the Tower monitoring Ground Control. Controller working ground was working about 4 aircraft and a vehicle. The vehicle was proceeding from the fire station requiring 2 runway crossings. The Ground Controller had an air carrier pushing back and a small aircraft he had taxied out to runway XY at intersection E for departure off runway XY. Aircraft X; VFR requesting taxi. Aircraft X was enroute to ZZZ. Certified Professional Controller (CPC) tells Aircraft X taxi runway XZL via romeo; delta; cross runway XY. Aircraft X read back the instructions but did not say cross runway AB. The Controller talks to another aircraft and then goes back and tells Aircraft X to make a left turn followed by an immediate right turn; cross runway AB. Aircraft X read back in my opinion was garbled (later in the elevator Controller agreed it was garbled but he understood it). I even said out loud 'nice radio'. The STARS display at Ground Control was covered by a sheet (more on this later) so I looked behind me at the STARS display at Local-2. I did not see any traffic on final but as I soon realized there was traffic on final. It must have been the distance or angle from the STARS display that told my mind there was not traffic. I looked back at Aircraft X and also noticed the Controller was heads down looking for a strip when I noticed Aircraft X was passing taxiway Delta and heading for runway XZL. I told the Controller he did not make his turn and the Controller took immediate action but unfortunately used the wrong call sign and talked to the aircraft who was holding short of runway AB. He told the aircraft to hold short of runway XZL. That pilot advised him he was holding short of runway AB. About the same time Aircraft X stopped short of the runway XZL surface area but past the hold short lines. The CPC then told Aircraft X to make an immediate 180 degree turn. Aircraft X complied and replied he was sorry. The Controller then gave instructions to get him on his way. About the time I noticed Aircraft X was not turning; out of the corner of my eye I noticed Aircraft Y over the numbers runway XZL. I am not 100% sure exactly where Aircraft Y turned right off the runway but it was prior to runway XY/AB.I really DON'T think what was going on in the tower was a contributing factor but feel I need to explain what was going on because a piece of equipment I would have used to see arrival aircraft was covered up. I also know that the Controller was not exactly in the space he would normally be; nor was his strips. We had 11 people in the Tower. Myself monitoring Ground Control; a Controller working Ground Control; Local Control; Flight Data/Clearance Delivery. Two workers installing film on the tower windows; a Tech Ops person watching them and another tech ops person working on the runway XL engine generator panel. We also had a CPC on GC-2 waiting for a brief from Ground Control (we were moving ground from Ground Control-1 to Ground Control-2 because the window people wanted to work on windows in front of Local Control and Ground Control where we normally work). We also had a Controller at Local-2 getting the briefing from Local-1 (we were moving this position to the other side of the tower).Window people had equipment laying around; stuff they had moved (like plexy glass) so they could work. They also had sheets over equipment in the area they were working. The Controller at Ground Control that I was watching had moved to his right to avoid them and had moved his strips off the bay and were laying in front of him on the counter thus a more heads down was required. The noise level was ok considering. I had actually told the workers to wait a couple minutes until we were able to move Ground Control to the other side of the tower so they would not block his view; they were complying. Again I'm not using this as any excuse but if I would have seen the traffic on final I might have had the Controller get a betterread back from Aircraft X on the second read back.I also feel the Controller was not in his comfort zone by having to move out of his space. Bottom line is the pilot did not follow instructions which resulted in the runway incursion and I believe the pilot knew he messed up because he said he was sorry. After situation happened my mind was going a million miles a minute and I forgot to have anyone issue Aircraft X the brasher statement. We did try and pass a message through TRACON but I'm not sure if pilot got the statement. When I have things happen it's no problem remembering this but for some reason because I had been so close to this situation it just slipped my mind to get this done. The Controller and I got relieved right after the event; the Controller was going to fill out an ATSAP and I went and told my Operations Manager.I should have looked out the window behind me to see if there was traffic instead of just looking at the STARS display. I believe I would have seen the flight and insisted on #2. Insist the Controller get a better read back on the second transmission.Pay better attention to call signs so if something like this happens again I could key up; override the Controller and tell the aircraft to stop or tell the Controller he was using wrong call sign. There would not had been that few second delay. Explain again to controllers the importance of clear read backs. Don't set pilots up to fail. Small aircraft generally do not have the experience professional pilots have so you have to treat them differently and spoon feed them; don't take any chances that close to an active runway especially with traffic on final.




Synopsis: Tower Controller reported an aircraft did not comply with taxi instructions and proceeded onto a runway another aircraft was landing on.