<< >> NASA ASRS Report 1285042, August 2015

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.

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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.