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A B737 on the sjc SILCN1 RNAV appeared high on profile to nct but the crew explained late ATC clearance to 'join the 30L localizer' prevents the FMS from calculating distances correctly. The FMC calculates the altitude to klide; back to gilro and the return to klide and causes a high approach. Crew managed the error manually.
| Attributes | |
| ACN | 1285042 |
| Time | |
| Date | 201508 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | SJC.Airport |
| State Reference | CA |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | B737 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Descent |
| Route In Use | STAR SILCN1 |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | FMS/FMC |
| Person 1 | |
| Function | Captain |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Experience | Flight Crew Last 90 Days 371 |
| Person 2 | |
| Function | First Officer |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Experience | Flight Crew Last 90 Days 233 |
| Events | |
| Anomaly | ATC Issue All Types Deviation - Procedural Published Material / Policy |
Narrative:
While on descent on the SILCN1 RNAV arrival; ATC informed us he thought we were coming in high. We rechecked our position/altitude and replied we showed that we were on the descent profile. We were cleared to 'descend via; landing west;' but had no further instructions (e.g.; 'join the 30L localizer.')on the SILCN1 RNAV arrival; all points after vlley are 'at or above.' since we don't close the arrival/approach discontinuity until cleared for the approach; the FMC thinks we're flying to klide (on the arrival); then back to gilro (on the approach); then again to klide. ATC stated it this way: 'company builds in an extra 20 miles;' which would be alleviated if (1) we had queried their intended follow-on clearance; or (2) ATC gave us 'join 30L localizer' early in the process.
Original NASA ASRS Text
Title: A B737 on the SJC SILCN1 RNAV appeared high on profile to NCT but the crew explained late ATC clearance to 'join the 30L Localizer' prevents the FMS from calculating distances correctly. The FMC calculates the altitude to KLIDE; back to GILRO and the return to KLIDE and causes a high approach. Crew managed the error manually.
Narrative: While on descent on the SILCN1 RNAV Arrival; ATC informed us he thought we were coming in high. We rechecked our position/altitude and replied we showed that we were on the descent profile. We were cleared to 'descend via; landing west;' but had no further instructions (e.g.; 'join the 30L Localizer.')On the SILCN1 RNAV Arrival; all points after VLLEY are 'At or Above.' Since we don't close the arrival/approach discontinuity until cleared for the approach; the FMC thinks we're flying to KLIDE (on the arrival); then back to GILRO (on the approach); then again to KLIDE. ATC stated it this way: 'Company builds in an extra 20 miles;' which would be alleviated if (1) we had queried their intended follow-on clearance; or (2) ATC gave us 'join 30L Localizer' early in the process.
Data retrieved from NASA's ASRS site 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.