B737 flight crew reported departing without realizing frost was present on the top of the wings.

Attributes
ACN	1600464
Time
Date	201812
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Taxi Parked
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 60 Flight Crew Total 13500 Flight Crew Type 4071
Person 2
Function	Pilot Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine Flight Crew Instrument
Events
Anomaly	Deviation - Procedural FAR Deviation - Procedural Published Material / Policy

Narrative:

The first officer accomplished the walk around and declared the aircraft 'good'. During cockpit checks the ground crew asked if we needed de-icing. I queried the first officer (first officer) and he said no. During taxi the lead flight attendant called to inform us that a pass riding crew member saw ice on the wing. I elected to pull over and have my first officer accomplish a wing check. The first officer checked the wings and had a short discussion with the passenger; a flight attendant. He still did not detect ice on the wing. We accomplished an uneventful takeoff and flight. On arrival a deadheading pilot approached us to say he saw frost on our wing. We agreed that company guidance precludes takeoff with any frost or ice on the top of the wing surfaces and that we simply didn't see any. We pledged to much more vigilant in the future.

Original NASA ASRS Text

Title: B737 flight crew reported departing without realizing frost was present on the top of the wings.

Narrative: The First Officer accomplished the walk around and declared the aircraft 'good'. During cockpit checks the ground crew asked if we needed de-icing. I queried the FO (First Officer) and he said no. During taxi the lead flight attendant called to inform us that a pass riding crew member saw ice on the wing. I elected to pull over and have my FO accomplish a wing check. The FO checked the wings and had a short discussion with the passenger; a Flight Attendant. He still did not detect ice on the wing. We accomplished an uneventful takeoff and flight. On arrival a deadheading pilot approached us to say he saw frost on our wing. We agreed that company guidance precludes takeoff with any frost or ice on the top of the wing surfaces and that we simply didn't see any. We pledged to much more vigilant in the future.

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.