Date: 202111
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737-900
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class B ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Hydraulic Main System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Troubleshooting; Situational Awareness
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Landed As Precaution; Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: At top of climb or early cruise we had a HYD light come on for Elec Hyd 1.  We followed the QRH which only instructed us to turn the pump switch off.  We observed the quantity and it showed 106% on the number 1 side and just under 100% on the number 2 side.  We assumed the pressure fell momentarily and entered a maintenance ELB report for intermittent low pressure.  During the flight we were watching the quantity fluctuate on the number 1 side from 90% to 106%.  After a while when we looked back down suddenly the number 1 side was at approx 25% quantity.  We watched it fluctuate up and down and as time went on and it continued to decrease.  We assumed that soon we would get a HYD SYS 1 failure and so we started reviewing the checklist for that as well as notifying dispatch and maintenance. We also told ATC we were monitoring low HYD indications and would let them know if we needed any assistance.  We discussed the possible need to divert and where would be the best options.  After considering our options we elected to continue to ZZZ since we still had HYD SYS 1 pressure above 2900.  We completed the QRH landing distances and had a thorough understanding of what we would have to accomplish if the system failed on the descent or approach.  We extended the gear early and it went down and locked normally.  The quantity indications went from 10% on the 1 side and 100% on the 2 side; to 25% and 80% (or something close to that); after the gear extension.  Landing was normal and we taxied to the gate normally and without incident.


Second narrative: Had the Hyd warning light illuminate at cruise. A HYD  system initially showed 106% quantity in ZZZ1. Ran the QRH for A HYD pump low pressure. As the A HYD quantity continued to fall; we conferred with ATC; Maintenance Control and Dispatch. Prepared to run the Loss of A system checklist but the quantity never dropped below 8%. [Requested priority handling] as a precaution and landed normally. There was enough fluid to use the normal nose gear steering. Inspected aircraft at gate and saw a puddle under the number 1 engine.


Synopsis: B737 flight crew reported hydraulic system pressure and quantity fluctuations at cruise and elected to continue to destination airport to make a precautionary landing.