Date: 201411
Local time of day: 0001-0600
Location: SAV.Airport, GA
Flight conditions: VMC
Light: Dawn
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: CTAF SAV; Center ZJX
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Situational Awareness
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Taxiway
Detector: Person Flight Crew
When detected: In-flight; Taxi
Result: General None Reported / Taken
Contributing factors: Human Factors; Chart Or Publication; Airport
Primary problem: Human Factors

Narrative: During preflight we discovered that the ATC tower would not be opening until XA:00. We pushed back; and made a radio call over CTAF of our planned taxi route of taxiway A; then E to runway 10. As we turned onto E I completed the taxi check and looked up to see some flashing lights on the taxiway as we approached E1. The captain slowed down his taxi pace to read the sign corresponding to the lights. We both mentioned that neither of us had seen flashing lights on a taxiway like that before. I don't remember the exact verbiage of the sign; but it stated something about the ILS critical area and a time range at the bottom. My initial thought was that the lights and sign meant that the ILS critical area is extended to this point when the tower is closed. At this point the captain had stopped the plane short of the lights and the captain and I both figured that it is VMC so the ILS critical area wasn't a factor. Even on IMC days we are rarely instructed to hold short of ILS critical areas. Unfortunately neither of us thought to review the Jepp 10-9 page and we continued to taxi down E to runway 10. As we crossed the lights I even noted that the standard ILS critical area markings were not even painted on the taxiway. We then communicated with Jacksonville center; made a call to CTAF and took off on runway 10. About 10-15 minutes into the flight the captain reviewed the SAV 10-9 and saw the note that read 'Twy E west of E1 closed when tower closed due to ILS critical area.' It was at this point we realized we had taxied on a closed taxiway. We unintentionally taxied onto a closed taxiway and although it didn't threaten the safety of the flight it was an error on our part. The error we made was to not investigate the reasoning for the unusual lights further by reviewing the SAV 10-9 page more closely.In the future I can take the time to investigate unusual taxiway markings further by studying the 10-9 more closely and by not just going with my preconceived notion of what the lights meant. The note on the 10-9 page does not really stick out when glancing over the 10-9 page because it is at a different part of the page from other notes and is not bolded. It would be helpful to add a note to the XJT -7 page regarding the closure of the taxiway when the tower is closed.




Synopsis: Air carrier flight crew taxiing to Runway 10 for takeoff on E at SAV failed to note the airport chart notation advising E is not available for taxi when the tower is closed due to the ILS critical area.