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A B737 FMC was programmed to cross a fix at FL270 45 NM after crossing the fix instead of 45 NM prior to crossing prior because the crew did not notice that '+' was entered instead of '-'.
| Attributes | |
| ACN | 934032 |
| Time | |
| Date | 201102 |
| Local Time Of Day | 1801-2400 |
| Place | |
| Locale Reference | ZZZ.ARTCC |
| State Reference | US |
| Environment | |
| Flight Conditions | VMC |
| Light | Night |
| Aircraft 1 | |
| Make Model Name | B737-500 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Descent |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | FMS/FMC |
| Person 1 | |
| Function | First Officer Pilot Not Flying |
| Experience | Flight Crew Last 90 Days 305 |
| Events | |
| Anomaly | Aircraft Equipment Problem Critical Conflict Airborne Conflict Deviation - Procedural Clearance |
Narrative:
I was getting out of the seat to use the restroom when the center cleared us to descend to fl 270 45 NM northwest of an enroute fix. The captain programmed the FMC (as the PF) and I verified the input while unstrapping. The FMC was actually programmed to descend to fl 270 45 NM southeast (the other side) because a '+' sign was entered instead of a '-' sign. We both missed it. Surprising; the legs page looks very similar regardless of how whether a '+' or '-' sign is entered. The center called when I was in the restroom and asked for an immediate descent below fl 300 to avoid traffic.
Original NASA ASRS Text
Title: A B737 FMC was programmed to cross a fix at FL270 45 NM after crossing the fix instead of 45 NM prior to crossing prior because the crew did not notice that '+' was entered instead of '-'.
Narrative: I was getting out of the seat to use the restroom when the Center cleared us to descend to FL 270 45 NM northwest of an enroute fix. The Captain programmed the FMC (as the PF) and I verified the input while unstrapping. The FMC was actually programmed to descend to FL 270 45 NM southeast (the other side) because a '+' sign was entered instead of a '-' sign. We both missed it. Surprising; the LEGS page looks very similar regardless of how whether a '+' or '-' sign is entered. The Center called when I was in the restroom and asked for an immediate descent below FL 300 to avoid traffic.
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.