B737 flight crew reported confusion on the planned landing flap setting.

Attributes
ACN	1562378
Time
Date	201807
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737 Next Generation Undifferentiated
Operating Under FAR Part	Part 121
Flight Phase	Final Approach
Flight Plan	IFR
Person 1
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Instrument Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 92
Person 2
Function	Captain Pilot Flying
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Deviation - Procedural Published Material / Policy Inflight Event / Encounter Unstabilized Approach

Narrative:

Approach and landing data was requested and reviewed for both flaps 30 and 40 for runways X and xx. Although both flap settings yielded acceptable data a flaps 40 visual to xx was briefed by the captain; I was first officer (first officer) and pm (pilot monitoring). We received clearance to fly the RNAV visual to xx and were stable and configured at flaps 30 with before landing checklist complete above 1000 feet. At about 400 feet I realized we were at flaps 30 instead of flaps 40 as briefed. I mentioned the discrepancy to the captain and he called for flaps 40; then immediately flaps 30. I moved the flap handle but don't believe the flaps actually moved because it was only a momentary selection. The captain briefed we were legal/safe with flaps 30; I agreed and he immediately called for me to re-complete the before landing checklist which was accomplished and we landed flaps 30 safely and without incident.

Original NASA ASRS Text

Title: B737 flight crew reported confusion on the planned landing flap setting.

Narrative: Approach and landing data was requested and reviewed for both flaps 30 and 40 for Runways X and XX. Although both flap settings yielded acceptable data a flaps 40 visual to XX was briefed by the Captain; I was F/O (First Officer) and PM (pilot monitoring). We received clearance to fly the RNAV Visual to XX and were stable and configured at flaps 30 with Before Landing Checklist complete above 1000 feet. At about 400 feet I realized we were at flaps 30 instead of flaps 40 as briefed. I mentioned the discrepancy to the Captain and he called for flaps 40; then immediately flaps 30. I moved the flap handle but don't believe the flaps actually moved because it was only a momentary selection. The Captain briefed we were legal/safe with flaps 30; I agreed and he immediately called for me to re-complete the Before Landing checklist which was accomplished and we landed flaps 30 safely and without incident.

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.