PA-23-250 Aztec
Flight Crew Flight Instructor; Flight Crew Commercial; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 200; Flight Crew Total 2000; Flight Crew Type 300
Time Pressure; Situational Awareness
Deviation / Discrepancy - Procedural Clearance; Ground Incursion Taxiway
Flight Crew Became Reoriented
Human Factors
I was holding short Runway XXL full length which is Taxiway X. I requested takeoff clearance. Tower had a fast jet coming in and the Controller told me to cross Runway XXL; but hold short Runway XXR at [Taxiway] X. I cleared XXL but I was actually holding short [Taxiway] Y. Tower called and gave me clearance to depart Runway XXR. I took a left on to Y thinking it was XXR and took off. I realized I was on the Taxiway Y right as my wheels left the ground. I sidestepped right and than tracked XXR. Luckily for me and everyone else there was no one crossing the taxiway.      I believe there were many things that caused the problem. I was late and rushing to get to a project on time. I had become pretty familiar with the airport and their operations. This caused me to be more relaxed and confident. While I normally always use my taxi diagrams I figured I didn't need it right in front of me. I knew exactly where I was going via the same taxiways I used many times. That all changed when I was told to cross to the right side and depart XXR. Next mistake was to take the intersection departure. I was asked if I could accept XXR at X which I agreed to. By taking the intersection departure I took away two things that would have helped me. Since it was an intersection departure I knew I wouldn't see the threshold or the numbers. When I didn't see either it did not bother me. I did a rolling takeoff and while on that roll my right engine shuddered just enough for me to look inside at my engine instruments. I then glanced at the airspeed and rotated. I never looked straight out down the taxiway. I used my peripheral vision. My head was just to inside the cockpit. My heading indicator and compass didn't help either as this was a parallel taxiway. Taxiway is good size which didn't help much either. Not the Tower's fault; but I also didn't get any radio calls. I'm almost 99.9 percent sure he actually didn't see it happen. I was the first to notice and I sidestepped the runway. I accidentally keyed the mic and said 'crap' that's when I believe Tower first noticed. The whole thing was bad and stupid; dumbest thing I've done in my life; airplane or not. Before this I had never even been close to making a big mistake like that. I will never let my guard down again. I will not accept intersection departures. I will maintain situational awareness and not rush.
PA23 pilot reported taking off on a parallel taxiway because of lack of situational awareness and time pressure.