Date: 201506
Local time of day: 1201-1800
Location: ZDC.ARTCC, VA
Flight conditions: Mixed
Weather elements / visibility: Thunderstorm
Light: Daylight
Aircraft: Cessna Citation Sovereign (C680)
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZDC
ATC / advisory: Center ZDC
Aircraft component: FMS/FMC
Component problem: Improperly Operated
Reporter organization: Air Taxi
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Human-Machine Interface; Fatigue; Confusion; Communication Breakdown
Second reporter function: Captain; Pilot Flying
Anomaly: ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Provided Assistance; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Human Factors; Procedure; Chart Or Publication
Primary problem: Chart Or Publication

Narrative: We were in route deviating through a line of weather. I believe we changed controllers when the new [controller] cleared us direct to 'Sin-Dee'. Controller spelled it out for us as 'Sierra-India...etc'. I was pilot monitoring (PM). I recorded the fix on paper. As I was writing the Captain plugged what was heard as 'CINDE' into the FMS. By the time I got done copying the fix he said Captain got 'Sin-Dee' already and asked what was after that. I told Captain and we proceeded along not yet catching the correct spelling as 'SINDE'. Somehow the captain typed a C. Maybe because the first syllable of 'Sierra' sounds like 'Cee'. I don't know. Somehow I didn't yet catch it. Usually when you do this the wrong fix is obviously wrong. This time was different.The resulting flight path on the MFD looked very reasonable as it took us around some weather and then to the airport. No big deal; right? That's when ATC asked us where we were going. Said we should have made a left turn. I told Controller we were going to 'Sin-Dee' and as I was saying it I looked and that's when I saw the pilot flying (PF) put in CINDE instead of SINDE. In the same breath I told ATC I was turning left and asked Controller to spell it again. We corrected everything never getting too far off course it. It was a heading error of about 30 degrees. Thankfully ATC was quick to recognize the error before it became a problem. Team work; right? Researching our flight we discovered that CINDE is the FAF to a VOR A approach to 3G4 airport in Ohio. This was southwest of CVG and reasonable as a route assignment. This is also not in Washington center's area so he wouldn't know about it. Two fixes that sound the same are best kept far away from each other. Also; the PF should have the PM who took the clearance put it in the box. However; had PF been the PM and I PF and PM copied the clearance and loaded the box I believe PM still would have said Sierra but typed C because that word is so commonly spelled that way and we were tasked with weather and arrival procedures. Again I am really surprised to see two fixes that sound the same so close to each other. Additionally we were over 10 hours of duty at this point and our cognitive responsiveness may not have been as high as it was earlier in the day. Removing any one of these by themselves may or may not have broken the error chain but together they all added up to a mistake. Again; I am greatful for the watchful eye of a controller who fixed the mistake before it became an issue.


Second narrative: While in cruise; ATC issued us new routing which began by having us proceeding directly to SINDE intersection. The fix name was spoken first; but despite ATC also spelling the fix; the name was copied as CINDE. The error in the first letter was not recognized; probably due to the more common spelling of the name 'Cindy' creating an expectation bias. Oddly; both CINDE and SINDE are located closely enough that the route appeared completely logical on the MFD; especially given that CINDE would take us away from convective weather ahead. One is northeast of CMH and the other is south of CMH; resulting in a roughly 30 deg. track divergence from our correct route as we proceeded to the wrong fix. About 2 min after turning towards the wrong fix; ATC queried us and respelled the fix; at which point the error was recognized and corrected.The reason for this error was the failure to correctly copy the fix spelling given by ATC; coupled with the existence of identical sounding fixes located so closely together. CINDE is a FAF on the VOR-A approach to Ashland Cty Airport (3G4) and is not a Low or High IFR enroute fix. SINDE is a High IFR fix on J149 west of AML VOR. We were about halfway between ESL VOR and MRB VOR when we got the reroute. Ordinarily; a clearance to a fix so far from XXX would've looked suspicious and been questioned. However; our previous route had us taking J134 from COLNS all the way to HNN VOR (well south of XXX) before turning north to XXX. Thus; from our particular position; and in light of the circuitous weather related routings; the incorrect fix looked valid.In this case; I admit that SOP was not followed. Despite being the pilot flying; I typed the fix into the scratch pad as my partner watched and acknowledged it to ATC. No excuses for that. However; had I been the non-pilot flying; responsible for FMS entry; I firmly believe the outcome would've been exactly the same. SOP was not the issue. It was a matter of attention; expectation bias; and a unique circumstance of position.


Synopsis: A CE-680 air crew; while enroute; were cleared to fix 'SINDE'. The Captain mistakenly typed the fix as 'CINDE'. The crew began to turn to the wrong fix when they were queried by ATC who also respelled the fix name. The crew entered the correct fix and proceeded as cleared. CINDE is 150 NM northwest of SINDE.