Narrative:

An emergency situation occurred en route during a scheduled air carrier flight from phx to ase. The #1 hydraulic system on the dhc-8 aircraft progressively lost fluid during cruise flight. The quantity indication dropped from over 1.5 quarts to just under 1.0 quart, which is less than the required minimum for this system. The #1 system operates the flaps, inboard roll spoilers, #1 rudder actuator, and normal braking including the antiskid. Prior to takeoff from phx, an excessively long taxi of 15-20 mins to the runway was encountered. The outside air temperature was over 100 degrees F. A quick attempt to xfer fluid from the #1 system to the #2 system prior to departure was unsuccessful. Both system were above departure minimums, but the #1 system quantity was showing close to the minimum requirement. After retracting the flaps on climb out, the #1 system quantity dropped slightly. As the flight progressed, the #1 system continued to show a decrease in quantity. With little over 1 quart indication on the flight deck gauge, the decision was made to contact the company dispatcher and maintenance controller for additional options. An emergency was declared with ZDV with a request to have emergency equipment standing by. A descent for the visual approach was started, but as the power was reduced, the #1 engine fuel pressure caution light illuminated. The fuel pump is engine driven and is unrelated to the hydraulic system. The fuel pressure abnormal checklist was completed, and the auxiliary fuel pump turned on extinguishing the caution light. The #1 hydraulic system abnormal checklists, including the in-range and landing, were completed. In an attempt to determine if the #1 hydraulic system services were operational, the flaps were extended normally without any indication of additional fluid loss. A normal approach and landing were made. After landing, the engines were shut down and the aircraft was towed to the gate to prevent the risk of normal brake failure. The follow-up with maintenance on the fuel pressure caution light pointed to a bad sensor, which was replaced. The #1 hydraulic system showed no signs of leaks, but the reservoir quantity in the wheel well indicated approximately .75 quart remaining. Maintenance's conclusion was: from an excessively long taxi in the high heat at phx, the hydraulic fluid heated and expanded showing a normal quantity for departure, but after the aircraft was airborne and the fluid was allowed to cool and contract, the fluid showed a steady decrease in quantity. The aircraft was svced, run up and tested for leaks. Nothing was found.

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Original NASA ASRS Text

Title: A DH8-200 IN CRUISE AT FL230 DECLARES AN EMER AND DIVERTS DUE TO LOW #1 HYD QUANTITY CAUSED BY ENVIRONMENTAL FLUID HEATING AND COOLING.

Narrative: AN EMER SIT OCCURRED ENRTE DURING A SCHEDULED ACR FLT FROM PHX TO ASE. THE #1 HYD SYS ON THE DHC-8 ACFT PROGRESSIVELY LOST FLUID DURING CRUISE FLT. THE QUANTITY INDICATION DROPPED FROM OVER 1.5 QUARTS TO JUST UNDER 1.0 QUART, WHICH IS LESS THAN THE REQUIRED MINIMUM FOR THIS SYS. THE #1 SYS OPERATES THE FLAPS, INBOARD ROLL SPOILERS, #1 RUDDER ACTUATOR, AND NORMAL BRAKING INCLUDING THE ANTISKID. PRIOR TO TKOF FROM PHX, AN EXCESSIVELY LONG TAXI OF 15-20 MINS TO THE RWY WAS ENCOUNTERED. THE OUTSIDE AIR TEMP WAS OVER 100 DEGS F. A QUICK ATTEMPT TO XFER FLUID FROM THE #1 SYS TO THE #2 SYS PRIOR TO DEP WAS UNSUCCESSFUL. BOTH SYS WERE ABOVE DEP MINIMUMS, BUT THE #1 SYS QUANTITY WAS SHOWING CLOSE TO THE MINIMUM REQUIREMENT. AFTER RETRACTING THE FLAPS ON CLBOUT, THE #1 SYS QUANTITY DROPPED SLIGHTLY. AS THE FLT PROGRESSED, THE #1 SYS CONTINUED TO SHOW A DECREASE IN QUANTITY. WITH LITTLE OVER 1 QUART INDICATION ON THE FLT DECK GAUGE, THE DECISION WAS MADE TO CONTACT THE COMPANY DISPATCHER AND MAINT CTLR FOR ADDITIONAL OPTIONS. AN EMER WAS DECLARED WITH ZDV WITH A REQUEST TO HAVE EMER EQUIP STANDING BY. A DSCNT FOR THE VISUAL APCH WAS STARTED, BUT AS THE PWR WAS REDUCED, THE #1 ENG FUEL PRESSURE CAUTION LIGHT ILLUMINATED. THE FUEL PUMP IS ENG DRIVEN AND IS UNRELATED TO THE HYD SYS. THE FUEL PRESSURE ABNORMAL CHKLIST WAS COMPLETED, AND THE AUX FUEL PUMP TURNED ON EXTINGUISHING THE CAUTION LIGHT. THE #1 HYD SYS ABNORMAL CHKLISTS, INCLUDING THE IN-RANGE AND LNDG, WERE COMPLETED. IN AN ATTEMPT TO DETERMINE IF THE #1 HYD SYS SVCS WERE OPERATIONAL, THE FLAPS WERE EXTENDED NORMALLY WITHOUT ANY INDICATION OF ADDITIONAL FLUID LOSS. A NORMAL APCH AND LNDG WERE MADE. AFTER LNDG, THE ENGS WERE SHUT DOWN AND THE ACFT WAS TOWED TO THE GATE TO PREVENT THE RISK OF NORMAL BRAKE FAILURE. THE FOLLOW-UP WITH MAINT ON THE FUEL PRESSURE CAUTION LIGHT POINTED TO A BAD SENSOR, WHICH WAS REPLACED. THE #1 HYD SYS SHOWED NO SIGNS OF LEAKS, BUT THE RESERVOIR QUANTITY IN THE WHEEL WELL INDICATED APPROX .75 QUART REMAINING. MAINT'S CONCLUSION WAS: FROM AN EXCESSIVELY LONG TAXI IN THE HIGH HEAT AT PHX, THE HYD FLUID HEATED AND EXPANDED SHOWING A NORMAL QUANTITY FOR DEP, BUT AFTER THE ACFT WAS AIRBORNE AND THE FLUID WAS ALLOWED TO COOL AND CONTRACT, THE FLUID SHOWED A STEADY DECREASE IN QUANTITY. THE ACFT WAS SVCED, RUN UP AND TESTED FOR LEAKS. NOTHING WAS FOUND.

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.