Date: 201709
Local time of day: 0601-1200
Location: ZLA.ARTCC, CA
Light: Daylight
Aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZLA
ATC / advisory: Center ZLA
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Troubleshooting; Communication Breakdown; Confusion
Second reporter function: Pilot Not Flying; Captain
Anomaly: ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Clearance
Contributing factors: Airspace Structure; Chart Or Publication
Primary problem: Airspace Structure

Narrative: While climbing out on the OSHNN8.NNAVY departure Los Angeles Center gave us a reroute for a new clearance approximately 5NM prior to PLAYY for a new clearance past PLAYY. We were cleared to climb from FL230 to FL240 and the reroute was after PLAYY direct YELAH then EED then flight planned route. The Captain read back the clearance as the Pilot monitoring and I quickly changed the altitude to FL240 confirming with him and input the first fix into the FMS. I entered YELLA and the FMS showed a 098 course for 58 miles which seemed to make sense. I confirmed the entry with the Captain and inserted the fix and the aircraft immediately started a turn. I then inserted EED into the FMS to clean up the flight plan and confirmed with the Captain that everything looked good. A few minutes later Center issued us a heading turn to 030 and then told us of a possible pilot deviation. The Captain told LA center that we had gone exactly where they had sent us and the controller said it was possible that we had gone to the incorrect YELAH. We then continued on the flight without any further incident. After the flight; the Captain called Center and they informed him that although we deviated from their desired course; there were no traffic conflicts or issues that resulted.This event occurred in my opinion due to two things. The first reason was that Center issued us a new clearance too close to the changed fix and in our rush to comply we did not take the time to confirm the correct spelling of one of the new fixes were were assigned that was not on our original flight plan. The second reason is that there are 2 fixes within 50 nautical miles of each that are pronounced the same; but spelled differently.  From the fix PLAYY where we were on the OSHNN8 departure; YELAH is a 038 course for 52 nautical miles and YELLA is a 098 course for 58 nautical miles.I suggest that we work with ATC to eliminate one of the YELLA or YELAH fixes to prevent a mistake like ours from happening again. I would also suggest that we immediately contact Center and have them inform controllers to be very careful when providing new clearances to aircrew that use either of these two fixes.


Second narrative: [Report narrative contained no additional information.]


Synopsis: Air carrier flight crew reported programming the wrong fix into the FMS due to similarly pronounced fixes YELLA and YELAH which are only 56 NM apart.