Date: 202109
Local time of day: 1201-1800
Location: STS.Airport, CA
Flight conditions: VMC
Weather elements / visibility: 9
Light: Daylight
Aircraft: Small Aircraft; High Wing; 1 Eng; Fixed Gear
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Takeoff / Launch
Airspace: Class D STS
ATC / advisory: Tower STS
Reporter organization: Personal
Reporter function: Single Pilot; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Private
Human factors: Human-Machine Interface; Communication Breakdown; Situational Awareness; Time Pressure; Confusion
Anomaly: Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Runway
Detector: Person Air Traffic Control; Person Flight Crew
When detected: Taxi
Result: Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Became Reoriented; Flight Crew Rejected Takeoff; General Flight Cancelled / Delayed
Contributing factors: Airport; Human Factors; Procedure
Primary problem: Human Factors

Narrative: I attempted take off from the wrong runway at STS; at a known hot spot (Taxiway Hotel at Runway 20). This is a stupid mistake that 'I would never make'; nonetheless; even after I made the mistake; I was not convinced that it happened; so much did I believe that I had lined up correctly. (This is one of the reasons for the delay in filing this report; I needed to convince myself that my impression of what happened was incorrect; and to revisit the scene of the crime.)I was in Aircraft X and started out by getting the ATIS. This included the runways in use (landing [Runway] 14; takeoff [Runway] 14 and [Runway] 20; and a caution about ensuring that one is on the correct runway before takeoff). I was aware of this and kept it in mind.With the airport diagram at hand; I got my taxi clearance ([Taxiway] A4; A; North Runup). I taxied along the edge of the ramp; ([Taxiway] Z; parallel to [Taxiway] A) but believed I was already on [Taxiway] A. As I believed I was on [Taxiway] A; I missed the [Taxiway] A4 entrance to the actual taxiway; and continued to [Taxiway] K; where I was surprised the taxiway ended. I stopped to check the diagram and get oriented; and ground control then cleared me via [Taxiway] K; A; North Ramp. I proceeded thus to the North Ramp; and read the signage about calling the Tower to get a runway assignment before taxiing further. I completed my runup; called the Tower; and was cleared 'hold short of Runway 20'. Taxiway H; right in front of me; led to the edge of Runway 20; and I proceeded to that point and held.I was in the right place. I did all the things. This was the correct runway. I was set.I was then given a clearance for immediate takeoff and advised of traffic on short final. An airplane was taking off at the time; and as I pulled onto the runway to follow; my thoughts were 'Man; they're packing them in tightly!' However; at Company they pack them in even closer; and this was not the time to have a discussion over the radio. My choice was accept or reject the clearance; and I had already accepted it and was in position. I did wait briefly until the aircraft in front left the ground; and then applied power to take off behind it; so that I had what I believed to be safe spacing; without dallying and using up the distance behind me that the following traffic would be dealing with.At that point the Tower canceled my takeoff clearance and told me to exit (I don't remember the actual verbiage; but my impression was to exit to the right). I pulled power back and started to the right; but there was no exit to the right. So I went to the left and exited at [Taxiway] A3; and was cleared to the North runup area.I was at this point still unaware that I had been on Runway 14 instead of [Runway] 20; as I was clearly at the correct runway prior to takeoff.I was subsequently given another clearance to hold short of Runway 20; and then a takeoff clearance; and I took off on Runway 20 without further incident.After landing and being told to phone the Tower; I still did not know what it is that I had done wrong. The illusion that I had turned onto the correct runway was so strong that it was only far later; when I realized that I could only have exited and taxied to the runup area if I was on [Runway] 14 at the time; that I realized that I must have somehow been on [Runway] 14.My post-flight review of the incident included reviewing the airport diagram; and also close-ups of aerial photographs of the [Runway] 14-20 intersection; including the airport markings. Two days later I went on a 'taxi tour' of the airport and did a takeoff from [Runway] 20 at Taxiway H with an instructor; to help prevent such an incident in the future.The pilot in command has the sole responsibility for the operation of the aircraft; and this incident was a failure of the pilot in command to operate with the degree of precision needed. Nonetheless; there are contributing factors that could be mitigated to break the error chain in other places; leading to a safer situation for all pilots.I had not flown at a complex airport in a long time (thank you Covid!); so my awareness of the need for extra awareness was not as sharp as it might have been. I should have planned my taxi route before moving; rather than as I proceeded. (This extends to post-landing taxi also.) Although I have operated out of this particular airport in the past; again; it was not recent; and I should have spoken to local pilots about the specifics of the hot spots in question. That said; while I was aware of the issue with wrong-runway departures; the thing I was not aware of was how easy it was to make that error. (More about that later.)At a hot spot where it is necessary to pause and verify the runway heading with the DG while on the runway; issuing an immediate takeoff clearance is asking for trouble. Pause to verify and one runs the risk of collision (or a deal). Fail to pause and verify runs the risk of wrong runway takeoff. And in the case that that the relevant traffic that leads to an immediate takeoff clearance is on Runway 14 and not Runway 20; it is technically possible to issue a 'position and hold 20' clearance; but this invites not only the error of holding on [Runway] 14 by mistake (as above); but the error of holding in position at the intersection. Of course; that's also a mistake 'I would never make'; but here we are. People make mistakes; this section is about reducing their probability and impact.That said; a clearance to take off on [Runway] 20 while [Runway] 14 is in use increases the efficiency of runway usage; and if all goes well; doubles the capacity of the airport. So there's a tradeoff there and I am not in a position to second-guess the air traffic controllers' decisions.When turning onto 'the runway' from Taxiway H; one makes a left turn. The pilot sits on the left; and the left edge of the taxiway and the left edge of the runway are very powerful alignment indicators. This is especially true for aircraft that sit low to the ground; where the runway ahead is not as evident as it might be for larger aircraft. I am pretty certain that I was using this 'left edge' to help me line up on 'the runway'; since I already knew I was at the correct runway. The stub of [Runway] 20 extends just enough from [Runway] 14 that as an aircraft turns into position; the other runway (and runway edge) comes into view; inducing the pilot to continue turning to line up on 'the runway'.Three possible mitigations come to mind; airport markings show that one of them is already partly in place. The yellow taxiway line already points straight onto [Runway] 20 without curving; though it once did curve. However; the left edge still curves. If the left edge lines of Taxiway H were also straight; the pilot would be led more strongly straight (and perpendicularly) onto Runway 20; and would be much less tempted to begin the turn onto the Runway (20) while close to the intersection of [Runway] 14. I believe it is the early turning onto the runway that leads pilots to continue too far; both using the left-edge effect I mentioned above; and due to the proximity of the next runway surface. Making the intersection of [Taxiway] H and [Runway] 20 strictly perpendicular may mitigate this risk to a meaningful extent; and is an easy fix.Additionally; the signage on [Taxiway] H at [Runway] 20 indicates only Runway 20. Signage indicating the proximity and angle of [Runway] 14 would go a long way towards reminding the pilot that they are not at 'the runway' (decision behind them) but at two runways; and must still be very mindful of picking the correct one (decision ahead of them). This is a slightly more involved solution as it requires constructing a runway sign. But I believe it will also greatly mitigate the issue.The two suggestions above; in conjunction; may significantly reduce the danger of wrong-runway takeoffs at this point on the airport; perhaps enough that it no longer would be a dangerous hot spot.A third option is to extend Runway 20 to Taxiway A; and eliminate Taxiway H. This will move the entry point to Runway 20 far enough from the intersection with [Runway] 14 that it becomes difficult to accidentally end up on [Runway] 14. This is admittedly quite involved and may be impractical for other reasons. I am not an airport designer; I'm just tossing out my ideas for what value they may have.None of this relieves the pilot in command of the responsibility to operate their aircraft safely. However; there are many links in an accident or incident chain; and these are the links that I can identify which contributed to the issue at hand.Note: 'time in type' is approximate and only counts Aircraft X and Aircraft X Variant Ceiling was unlimited.




Synopsis: Pilot reported confusion during taxi for takeoff and lined up on the wrong runway for departure from STS airport. ATC notified pilot and the pilot taxied to the correct runway.