B737-800
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Confusion; Human-Machine Interface; Training / Qualification
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance
Human Factors
Flight plan included 4 waypoints identified by 5 digits only (49105 47098 46093 46091). Dispatch identified these as lat/longs. I interpreted this to mean cardinal lat/longs. These abbreviated waypoint IDs were in the flight plan routing strip and in both the left and right margin position columns of the flight plan body. We programmed cardinal lat/Longs in a manner similar to the Oceanic convention for waypoint naming (i.e. 49105 was programmed as N49W105). Shortly after leaving first named fix (YQL) enroute to first numbered fix (49105) Winnipeg Center queried about our routing. We replied that we were proceeding to N49W105 - we were told that our clearance was to N4929.0/W10526.0. The same type of discrepancy was true for the other 3 numbered waypoints. When we checked the lat/longs for the numbered waypoints in the flight plan body we found that they matched ATC expectations and the actual filed routing. We had not seen this waypoint naming convention before and could not find reference in the FOM. It is my job as Captain to keep the airplane on course; thus I take full responsibility for this error and; clearly; this is a lesson learned. Perhaps a note to crews about this would prevent the next pilot from making the same mistake.
The Captain of an A320 mistook five digit lat/long 'cardinal' coordinates in his flat plan route for the more precise eleven digit local they represented and which were shown in the fix lat/long column of his leg by leg flight plan. ATC noted the resulting modest track deviation and the problem was corrected.