B737 flight crew reported overshooting an altitude restriction in descent due to a programming error...

Attributes
ACN	1765382
Time
Date	202010
Local Time Of Day	0601-1200
Place
Locale Reference	SAN.Airport
State Reference	CA
Environment
Light	Daylight
Aircraft 1
Make Model Name	B737 Next Generation Undifferentiated
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Person 1
Function	Pilot Flying First Officer
Qualification	Flight Crew Instrument Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 150 Flight Crew Type 7500
Person 2
Function	Captain Pilot Not Flying
Qualification	Flight Crew Instrument Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 60
Events
Anomaly	Deviation - Altitude Crossing Restriction Not Met Deviation - Altitude Overshoot Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Inflight Event / Encounter Wake Vortex Encounter Inflight Event / Encounter Weather / Turbulence

Narrative:

We were cleared to descend via the arrival except maintain 12;000 ft. We were cruising at 24;000 ft northeast of momar. We began to experience turbulence that resembled wake. At that point in time I was under the impression we were cleared to 12;000 ft. I selected altitude intervention to begin a descent out of the turbulence. I selected altitude intervention a second time to begin the descent. The crossing attitudes were erased at momar due to selecting altitude intervene. During both presses of the altitude intervene the captain and I vvmi'd. We descended below the published altitude at momar.

Original NASA ASRS Text

Title: B737 Flight Crew reported overshooting an altitude restriction in descent due to a programming error.

Narrative: We were cleared to descend via the arrival except maintain 12;000 ft. We were cruising at 24;000 ft northeast of MOMAR. We began to experience turbulence that resembled wake. At that point in time I was under the impression we were cleared to 12;000 ft. I selected Altitude Intervention to begin a descent out of the turbulence. I selected Altitude Intervention a second time to begin the descent. The crossing attitudes were erased at MOMAR due to selecting ALT Intervene. During both presses of the ALT Intervene the Captain and I VVMI'd. We descended below the published altitude at MOMAR.

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.