B737-700
Flight Crew Last 90 Days 111; Flight Crew Type 237
Communication Breakdown; Confusion; Other / Unknown
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Procedure; Human Factors
We both verified the fix in the FMS before executing direct. While talking to Chicago Center around 45 minutes later; they asked what fix we had last been cleared to. I responded with TRAGG. He asked if we were direct to TRAGG; as he was showing us flying north of course. I confirmed we were direct to TRAGG and spelled the fix phonetically. He then replied with a clearance to TRAKK intersection. It seems the easiest way to avoid this situation is absolute diligence when reprogramming the FMC. The flight plan was eight or nine pages long; and it was easy to skip a page when looking for the correct waypoint. We both saw what we thought was the correct waypoint; and the PM verified with the PF before the change was executed. A quick glance at the paper release could have possibly revealed there were two very similar sounding waypoints on the flight plan.
After reaching a cruise altitude we asked ATC for a shortcut. ATC issued a clearance to the fix; TRAGG; on the BOJID 1 RNAV Arrival. Pilot Flying scrolled through the FMC pages and found the fix with Pilot Monitoring observing and verifying the fix; TRAGG. Nearly 45 minutes later; ATC queried us on our direct navigation towards TRAGG. We confirm that we are direct TRAGG. Minutes later ATC queries us again about our navigation to TRAGG. We then phonetically spell out the fix TRAGG. ATC informs us that TRAGG was not the fix we were given direct to. The fix ATC intended us to fly direct was TRAKK. During our FMC selection; we do not ever remember seeing the fix TRAKK. After further review; the fix; TRAKK; was discovered to be on our original flight plan. ATC did not seem too concerned about the mix up; but redirected us direct to TRAKK. We complied immediately. Both PF and PM were convinced that ATC issued us a clearance direct TRAGG. Our read back of the original clearance did not alert ATC. With two fixes on the same route with almost identical spelling and pronunciation; it can be extremely easy to overlook the ambiguity. In the future; it may help for both pilots to verify the entire route more thoroughly before selection of fixes.
B737 crew is cleared direct to what they believe is TRAGG. Some time later ATC questions the crew on their navigation and it is discovered that they should be proceeding direct to TRAKK.