Flight Crew Instrument; Flight Crew Commercial; Flight Crew Flight Instructor
Flight Crew Last 90 Days 203; Flight Crew Total 1405; Flight Crew Type 830
Communication Breakdown; Confusion; Situational Awareness
Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Human Factors
I was giving aircraft familiarization training to a new owner in his aircraft. We were taxiing from the FBO to Runway XX. Per taxi instructions given by Ground we were to taxi south on Taxiway XX and hold short of Taxiway XY. Upon reaching Taxiway XY; Tower instructed us to hold short of Runway XX. We then proceeded across the hold short line at Taxiway XY to cross the under-construction runway expecting to see an additional hold short line at the actual active runway. As soon as we realized that we had crossed the only hold short line we immediately stopped and contacted Tower asking for further instruction. The other single engine aircraft on final was instructed to go around and we were given a takeoff clearance after receiving a phone number to contact from Tower.We did listen to the ATIS during our run-up and discussed the possibility of 'non-standard' hold short lines. In hindsight; we should not have crossed the hold short lines at Taxiway XY without being 100% certain that we were authorized to do so. Knowing that the main runway at ZZZ was under-construction we should have been exercising extreme caution to avoid this type of situation. I think the main contributing factors to this occurrence was the unusual taxi and airport environments due to the construction. I have not seen a hold short line as far from the active runway as it is at ZZZ. Another confusing factor was the change in instruction/language between the Ground Controller and Tower Controller. Ground instructed us to hold short of Taxiway XY which was in essence the correct spot to hold for the active runway. When switching to Tower we were instructed to hold short of Runway XX. This made us believe we were to proceed to a different location.  Of course; both of us as experienced pilots should have caught this and the blame falls solely on us. I understand the importance of safety of ground operations and will use this as a valuable lesson in my personal flying as well as when instructing in the future.
I was receiving transition training in my new airplane. My Instructor and I were taxing onto Taxiway XX to hold short of Taxiway XY for departure on Runway XX at ZZZ. Once we were holding short of Taxiway XY; Ground instructed us to contact Tower. We contacted the Tower and were told to hold short of Runway XX. ZZZ's main runway is under construction and is closed to operations; it has large X's on that runway. There is a hold short line at the intersection of Taxiway XY and the closed runway. The ATIS notes there are 'non-standard markings' for the runway.My Instructor had been to ZZZ [a month ago]. We discussed the 'non-standard markings' and thought there would be another set of hold short lines just before the active; not under construction Runway XX. After crossing the previously mentioned hold short line; we were looking ahead towards the open Runway XX and did not see any hold short lines. We then immediately stopped and were at the intersection of Taxiway XY and the approach end of the under construction; closed Runway XX. We then asked the Tower if we were ok stopping in our present position; and he said no and that we should have stopped at the hold short lines behind us. We continued to hold our position and Tower instructed an aircraft on final for Runway XX to go around. We were still several hundred ft. from the active Runway XX. In retrospect; we should have asked the Tower exactly where the hold short lines were for Runway XX. The term 'non-standard markings' is a bit vague and our interpretation of that was that there were hold short lines for the closed Runway XX and also hold short lines for the open and active Runway XX. I'm not excusing our actions; but I think it would be very helpful to have the ATIS remark that the hold short lines at the intersection of Taxiway XY and the closed; under construction runway are the ones to be used for all operations. Thank You.
Flight Instructor and Student reported experiencing confusion with instructions from ATC and crossed past the hold short line without clearance.