Date: 201503
Local time of day: 1201-1800
Location: IAD.Airport, DC
Flight conditions: VMC
Light: Daylight
Aircraft: Small Transport; Low Wing; 2 Turbojet Eng
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Ground IAD
Reporter organization: Corporate
Reporter function: Captain
Reporter qualification: Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Communication Breakdown
Anomaly: Deviation / Discrepancy - Procedural Clearance; Ground Incursion Taxiway
Detector: Person Air Traffic Control
When detected: Taxi
Result: Air Traffic Control Issued Advisory / Alert
Contributing factors: Human Factors; Chart Or Publication; Airport; Procedure
Primary problem: Airport

Narrative: We were cleared to taxi to Runway 30 from the General Aviation ramp; via southbound on taxiway Z; to hold short of Y11. My First Officer thought the clearance was to hold short of the runway on Y11. As we approached Y11; I slowed to hold short; and the First Officer said it was a left turn to hold short on Y11. The signage and the Jeppessen chart displayed in the cockpit did not clearly depict where Y11 began and ended. I should have recognized the confusion; and asked ATC for clarification; but instead turned onto Y11 and proceeded to the end of it. As I recall; the Y11 sign to our right had an arrow pointing left; and there was another Y11 sign near the Q stub to runway 30; placed at an angle that made it look like it was only the stub portion ahead; so I momentarily thought Y11 was actually just the short stub leading to Q and we were on the holding block area.I held short of Q; which I thought was holding short of the short stub Y11.Ground Control notified us of our error; and we asked if they would like us to taxi away and onto the holding block; and they said to just hold our position; which we did. There was only one other aircraft in the area; and they must have been well behind us or to our right; because they were cleared around us via Y and Q to takeoff ahead of us. There were no potential conflicts with other aircraft; but it was very disconcerting to have made this error when we were trying to do the right thing.The NOS chart and Jeppesen chart depict Y11 only to the west of Z; so [as it appears on the Jeppesen chart; Y11 short of Taxiway Q] looks like a stub [off] the holding block. Painting Y11 with an arrow on the taxiway surface itself would alleviate this confusion; because the entire area is paved; and it seems like we are on a holding block when we are actually utilizing a portion of that holding block as Y11. They could also paint a sideline paralleling the taxiway centerline to represent the width of taxiway Y11; and differentiate it from the holding block.The Jeppesen and NOS charts should also depict Y11 as running the entire length of the south end of the holding block by printing Y11 twice along that segment; as they have done with taxiways Q; U; Z; and J elsewhere on the chart.




Synopsis: A corporate flight crew cleared from the IAD General Aviation ramp to Runway 30 via Z; hold short of Y11 failed to note that the south end of the 'HOLD BLOCK' just prior to the Runway 30/parallel Taxiway Q complex; through which Z traverses is technically Taxiway Y11. They thus held short of Q while on Y11.