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A B737-700 turned 10 miles before an airway fix in order to intercept the course to the next fix. ATC queried the crew about the early turn and was told that that fix was not a fly over and that some aircraft turn earlier than others.
| Attributes | |
| ACN | 864471 |
| Time | |
| Date | 200912 |
| Local Time Of Day | 0601-1200 |
| Place | |
| Locale Reference | ZZZ.ARTCC |
| State Reference | US |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | B737-700 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Climb |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | FMS/FMC |
| Person 1 | |
| Function | Captain |
| Experience | Flight Crew Last 90 Days 234 |
| Person 2 | |
| Function | First Officer |
| Experience | Flight Crew Last 90 Days 220 |
| Events | |
| Anomaly | Airspace Violation All Types Deviation - Procedural Other / Unknown |
Narrative:
On climbout we were switched to departure. We were given an easterly heading and then 'cleared on course.' the FMC was correctly programmed and LNAV selected with the autopilot engaged. As always; we never made it to the first navaid as LNAV turns us well before reaching it to intercept the course to the next point. The controller asked us why he sees company turn prior to that fix anywhere between five and ten miles. He correctly reported that we were ten miles from it and in 'someone else's' airspace. I responded that that VOR is not defined as a flyover point and that the aircraft intercepts the course between it and the next fix. I added (hopefully correctly) that we have different versions of navigational software that may account for the mileage differences he sees. The controller didn't indicate that there was any problem; but seemed to be just expressing his own curiosity.
Original NASA ASRS Text
Title: A B737-700 turned 10 miles before an airway fix in order to intercept the course to the next fix. ATC queried the crew about the early turn and was told that that fix was not a fly over and that some aircraft turn earlier than others.
Narrative: On climbout we were switched to Departure. We were given an easterly heading and then 'cleared on course.' The FMC was correctly programmed and LNAV selected with the autopilot engaged. As always; we never made it to the first navaid as LNAV turns us well before reaching it to intercept the course to the next point. The Controller asked us why he sees Company turn prior to that fix anywhere between five and ten miles. He correctly reported that we were ten miles from it and in 'someone else's' airspace. I responded that that VOR is not defined as a flyover point and that the aircraft intercepts the course between it and the next fix. I added (hopefully correctly) that we have different versions of navigational software that may account for the mileage differences he sees. The Controller didn't indicate that there was any problem; but seemed to be just expressing his own curiosity.
Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.