Date: 201510
Local time of day: 1201-1800
Location: ZME.ARTCC, TN
Flight conditions: Mixed
Light: Daylight
Aircraft: MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZME
ATC / advisory: Center ZME
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Situational Awareness
Anomaly: Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: Flight Plan on Dispatch Release; KXNA DCT RZC DCT GAGLE DCT SZW DCT OCF V159 LEESE DCT [ZZZ1]FMS Flight Plan; KXNA DCT RZC DCT GABLE DCT SZW DCT OCF DCT ALADN DCT CUSAB DCT SHIMM DCT LEESE DCT [ZZZ1] (note that Victor Airway 159 is not in FMS database)ATC Clearance; HIFIL4 Departure as filed; Climb 5;000 to feet; Expect FL 370 in: 10 minutes; Departure Frequency 121.0; Squawk 5661.We neglected to catch a waypoint fix input error while programming the FMS for a ferry flight. We didn't discover the error until we were queried by ATC during climb-out to our cruise altitude. I input the route and had entered 'GABLE' as our second fix instead of 'GAGLE'.I input the route into the FMS and checked it for accuracy. The only thing I don't recall doing; which likely would have lead me to catch the input error; was checking the total route mileage against the mileage on the flight plan. It's one of the additional FMS programming steps used in long range navigation that is not really addressed for general FMS programming. Despite the fact that 'GABLE' and 'GAGLE' are in the same general direction from RZC VOR; had we checked; the total mileage for the route would have been different between the FMS and the flight plan.Additionally; on most revenue flights; we likely would have had an FMS 'insufficient fuel' message due to the erroneous total distance; but since it was a ferry flight that had been fueled the night before for revenue service; we had 4;700 lbs. of extra fuel onboard; more than enough to cover the extra mileage.As we climbed out of XNA; we were given ATC clearance to deviate as necessary around local rain showers; and then cleared direct 'GAGLE'; which I read back as 'GABLE'. Once clear of the shower activity; we erroneously proceeded direct to 'GABLE' instead of 'GAGLE' using the FMS. After a couple of frequency changes during climb-out; we checked in with a Memphis Center controller who asked if were still deviating around weather. After I responded we were direct 'GABLE' (which I assume he understood as 'GAGLE'); he responded that we should check that; as it didn't appear that we were direct. As we looked at the route and the FMS; the controller cleared us direct to SZW. Shortly thereafter; we discovered the original programming error and I announced to the controller that we had discovered and corrected the problem. The controller did not seem concerned and gave us another frequency change.




Synopsis: MD80 Captain reported a track deviation that involved confusion between two similar sounding fix names.