B737-800 flight crew reported loss of hydraulic system during cruise.

Attributes
ACN	1747363
Time
Date	202006
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Light	Daylight
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Vectors
Flight Plan	IFR
Component
Aircraft Component	Hydraulic System Pump
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Pilot Not Flying Captain
Qualification	Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Instructor
Events
Anomaly	Aircraft Equipment Problem Critical

Narrative:

Approximately ten minutes after reaching cruise altitude FL360 we saw the master caution flicker. No light on recall. 2 minutes after that we had a steady master caution with hyd (hydraulic) light on recall. At that point we determined that it was system B through illumination of the low pressure lights as well as falling system B pressure on hydraulic page. We [requested priority handling] with center and requested vectors back to ZZZ. Set up for the ILS xx direct [the initial fix] and the ca (captain) went through the QRH as we headed back. Uneventful flaps 15 landing; greeted by fire rescue and they followed us to [the gate].

Original NASA ASRS Text

Title: B737-800 flight crew reported loss of hydraulic system during cruise.

Narrative: Approximately ten minutes after reaching cruise altitude FL360 we saw the master caution flicker. No light on recall. 2 minutes after that we had a steady master caution with hyd (hydraulic) light on recall. At that point we determined that it was System B through illumination of the low pressure lights as well as falling system B pressure on Hydraulic page. We [requested priority handling] with Center and requested vectors back to ZZZ. Set up for the ILS XX direct [the initial fix] and the CA (Captain) went through the QRH as we headed back. Uneventful flaps 15 landing; greeted by Fire rescue and they followed us to [the gate].

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.