Date: 202104
Local time of day: 0601-1200
Location: BOI.Airport, ID
Flight conditions: VMC
Weather elements / visibility: 10
Light: Dawn
Aircraft: Single Engine Turboprop Undifferentiated
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
Airspace: Class C BOI
ATC / advisory: Tower BOI
Reporter organization: Air Taxi
Reporter function: Captain; Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Distraction; Fatigue
Anomaly: Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Excursion Runway
Detector: Person Flight Crew
When detected: Taxi
Result: Air Traffic Control Provided Assistance; Aircraft Equipment Problem Dissipated; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Overcame Equipment Problem; General Maintenance Action
Contributing factors: Airport; Human Factors
Primary problem: Human Factors

Narrative: I was cleared to land on 10R and planned to exit at the first available taxiway (H) which was within the landing performance data but required accurate; prompt control to do so. I successfully landed and slowed to normal exit speed; acquired what I thought was the lead-off line for H; and the taxiway edge lights on the far side of the lead-off line. What I didn't perceive was that the lead-off line had been blacked out recently as H had been moved during construction. Given the poor ambient lighting (even accounting for the excellent forward lighting from the landing lights); there was no immediate visual difference between the runway surface and the transition to the gravel surface and as the airplane departed the runway; the extra drag of the gravel and ~4' of underlying mud brought the airplane to a stop. After realizing what had happened and that I wasn't going to be able to taxi further; I coordinated with Tower; was instructed to switch to Ground and asked for a tow and passenger transport; then shut down the engine.Everything but the runway exit went as planned. I followed aircraft procedures; but departed from my usual night time post-landing technique of acquiring the lead-off line; then verifying the taxiway signage and seeing the lead-off goes between the edge lights. The erroneous lead-off line combined with the adjacent line of taxiway edge lights and the still-night-but-approaching-daylight contributed to my disregard of my usual next exit criterion that the lead-off lights guide between the taxiway lights; resulting in exiting the runway surface next to the intended taxiway exactly on the blacked out lead-off line that led to the previous location of Taxiway H.The bottom line contributors were fatigue after an earlier transport; planning an aggressive landing while fatigued; and visual cues that combined with my disregard of solid techniques in the process of achieving the required performance to meet the plan. In the future I will accept and use the available runway rather than plan for an expedited profile that approaches the limits of my current capabilities.




Synopsis: Pilot reported a runway excursion during landing at BOI due to ambiguous lead-off runway and taxiway edge lighting configuration.