B737 flight crew reported being below crossing restriction while reprogramming FMS.

Attributes
ACN	1618346
Time
Date	201902
Local Time Of Day	0601-1200
Place
Locale Reference	SJC.Airport
State Reference	CA
Environment
Flight Conditions	IMC
Aircraft 1
Make Model Name	B737-900
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	STAR SILCN4
Flight Plan	IFR
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 185 Flight Crew Total 28800 Flight Crew Type 11326
Person 2
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Multiengine Flight Crew Instrument
Experience	Flight Crew Last 90 Days 223 Flight Crew Total 7253
Events
Anomaly	ATC Issue All Types Deviation - Altitude Crossing Restriction Not Met Deviation - Altitude Overshoot Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Inflight Event / Encounter Weather / Turbulence

Narrative:

We were inbound to sjc on the SILCN4 arrival when we were cleared to FL240. We were told to slow to 250. A short time later we were told to maintain 250 until silcn and then speed up to 280. The FL240 descent clearance had our altitude covered at silcn so I used vertical speed to maintain the 250 kts and put 280 kts into the FMC to use when we crossed silcn. Before that all happened we got a third speed change to go back to 250 kts. Eventually we got a descend via clearance. I can't remember exactly when or at what altitude we got the descent via clearance. Right before crossing vlley I noticed on the prog page that we had crossed silcn at 18;800 which could have been 1;200 feet low if we were descending via at that point. Things were changing very quickly so unfortunately I can't recall every detail.

Original NASA ASRS Text

Title: B737 flight crew reported being below crossing restriction while reprogramming FMS.

Narrative: We were inbound to SJC on the SILCN4 arrival when we were cleared to FL240. We were told to slow to 250. A short time later we were told to maintain 250 until SILCN and then speed up to 280. The FL240 descent clearance had our altitude covered at SILCN so I used vertical speed to maintain the 250 kts and put 280 kts into the FMC to use when we crossed SILCN. Before that all happened we got a third speed change to go back to 250 kts. Eventually we got a descend via clearance. I can't remember exactly when or at what altitude we got the descent via clearance. Right before crossing VLLEY I noticed on the Prog page that we had crossed SILCN at 18;800 which could have been 1;200 feet low if we were descending via at that point. Things were changing very quickly so unfortunately I can't recall every detail.

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.