A B737-200 returned to the field due to an apparent loss of 'a' system hydraulic quantity.

Attributes
ACN	364085
Time
Date	199703
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : cos
State Reference	CO
Altitude	msl bound lower : 9000 msl bound upper : 9000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : cos
Operator	common carrier : air carrier
Make Model Name	B737-200
Operating Under FAR Part	Part 121
Flight Phase	climbout : initial climbout : takeoff other
Route In Use	approach : visual arrival other departure other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 250 flight time total : 8500 flight time type : 6400
ASRS Report	364085
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 270 flight time total : 16500 flight time type : 8000
ASRS Report	364096
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Normal departure out of cos until I raised the landing gear. The 'a' system low quantity light illuminated (hydraulic) and the 'a' system hydraulic quantity gauge indicated 1.8 gals of fluid remaining. We proceeded to watch the gauge, it continued showing a decrease in quantity. We elected and agreed to return to field (cos), leveled at 9000 ft, turned downwind for runway 17L. I informed the cabin crew that we were returning to cos as a precautionary measure with a possible hydraulic leak and would be on the ground in approximately 4 mins. I then communicated with company and informed them that we were returning to cos within a few mins. I also informed the passenger of our situation. We completed the ldng checklist approximately 800 ft AGL. I then asked the captain if there was anything else he needed me to accomplish and he stated that he would like me to monitor the remainder of the approach and landing with him. I then made the required 500 ft AGL callout we landed normally with no further problems and proceeded to the gate. Maintenance control contacted us as well as contract maintenance, they inspected the aircraft, filled the hydraulic system, found no leaks.

Original NASA ASRS Text

Title: A B737-200 RETURNED TO THE FIELD DUE TO AN APPARENT LOSS OF 'A' SYS HYD QUANTITY.

Narrative: NORMAL DEP OUT OF COS UNTIL I RAISED THE LNDG GEAR. THE 'A' SYS LOW QUANTITY LIGHT ILLUMINATED (HYD) AND THE 'A' SYS HYD QUANTITY GAUGE INDICATED 1.8 GALS OF FLUID REMAINING. WE PROCEEDED TO WATCH THE GAUGE, IT CONTINUED SHOWING A DECREASE IN QUANTITY. WE ELECTED AND AGREED TO RETURN TO FIELD (COS), LEVELED AT 9000 FT, TURNED DOWNWIND FOR RWY 17L. I INFORMED THE CABIN CREW THAT WE WERE RETURNING TO COS AS A PRECAUTIONARY MEASURE WITH A POSSIBLE HYD LEAK AND WOULD BE ON THE GND IN APPROX 4 MINS. I THEN COMMUNICATED WITH COMPANY AND INFORMED THEM THAT WE WERE RETURNING TO COS WITHIN A FEW MINS. I ALSO INFORMED THE PAX OF OUR SIT. WE COMPLETED THE LDNG CHKLIST APPROX 800 FT AGL. I THEN ASKED THE CAPT IF THERE WAS ANYTHING ELSE HE NEEDED ME TO ACCOMPLISH AND HE STATED THAT HE WOULD LIKE ME TO MONITOR THE REMAINDER OF THE APCH AND LNDG WITH HIM. I THEN MADE THE REQUIRED 500 FT AGL CALLOUT WE LANDED NORMALLY WITH NO FURTHER PROBS AND PROCEEDED TO THE GATE. MAINT CTL CONTACTED US AS WELL AS CONTRACT MAINT, THEY INSPECTED THE ACFT, FILLED THE HYD SYS, FOUND NO LEAKS.

Data retrieved from NASA's ASRS site as of July 2007 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.