B737 first officer reported a flap malfunction on final approach.

Attributes
ACN	1428566
Time
Date	201703
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Light	Night
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Final Approach
Flight Plan	IFR
Component
Aircraft Component	Trailing Edge Flap
Person 1
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy Inflight Event / Encounter Weather / Turbulence

Narrative:

During approach and completing mechanical checklist crew became aware flap handle selected for flaps 30 but flap indicator showed flaps set at 25 and a green light. Captain ordered a go around and maintained configuration while I handled the radio and checklist. This event occurred after a long two leg all night flight and the conditions were nighttime windy and moderate turbulence at low altitude. We completed the checklist and returned to runway xxl. On short final we received a; 'too low flaps'; and 'terrain terrain' GPWS warning because I misread the non-normal checklist item calling for flap inhibit to be engaged. I attribute this misread to several factors. I was tired; this was a brutal trip assignment; it was turbulent and I was dividing my attention between the checklist and monitoring the aircraft status i.e. Airspeed control radio and other set up functions.

Original NASA ASRS Text

Title: B737 First Officer reported a flap malfunction on final approach.

Narrative: During approach and completing mechanical checklist crew became aware flap handle selected for flaps 30 but flap indicator showed flaps set at 25 and a green light. Captain ordered a go around and maintained configuration while I handled the radio and checklist. This event occurred after a long two leg all night flight and the conditions were nighttime windy and moderate turbulence at low altitude. We completed the checklist and returned to Runway XXL. On short final we received a; 'TOO LOW FLAPS'; and 'TERRAIN TERRAIN' GPWS warning because I misread the non-normal checklist item calling for flap inhibit to be engaged. I attribute this misread to several factors. I was tired; this was a brutal trip assignment; it was turbulent and I was dividing my attention between the checklist and monitoring the aircraft status i.e. airspeed control radio and other set up functions.

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.