B737 first officer reported a 'too low flaps' warning at 500 ft on an ILS approach.

Attributes
ACN	1511658
Time
Date	201801
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 29
Events
Anomaly	Deviation - Procedural Published Material / Policy Flight Deck / Cabin / Aircraft Event Other / Unknown Inflight Event / Encounter Unstabilized Approach

Narrative:

ILS into ZZZ. Arrival was accompanied by several STAR changes; vectors off and back on STAR; speed changes; general communication saturation; and weather less than expected. Approach was briefed as a flaps 30 approach. At approximately 500 ft; too low flaps; was broadcast by the aircraft. It was communicated and elected to put the flaps to 30 and continue the approach. I believe confirmation-bias played into us announcing 'flaps 30' during the before landing checklist with the flap position needles being 'in the ballpark' of where we are used to seeing them for a flaps 30 approach.

Original NASA ASRS Text

Title: B737 First Officer reported a 'TOO LOW FLAPS' warning at 500 ft on an ILS approach.

Narrative: ILS into ZZZ. Arrival was accompanied by several STAR changes; vectors off and back on STAR; speed changes; general Communication saturation; and weather less than expected. Approach was briefed as a flaps 30 approach. At approximately 500 ft; TOO LOW FLAPS; was broadcast by the aircraft. It was communicated and elected to put the flaps to 30 and continue the approach. I believe confirmation-bias played into us announcing 'flaps 30' during the Before Landing Checklist with the flap position needles being 'in the ballpark' of where we are used to seeing them for a flaps 30 approach.

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.