Narrative:

Two hours after takeoff, while in cruise at FL410, we noticed hydraulic pressure dropping slowly through 1200 psi. Approximately 10 mins later pressure had dropped to 1000 psi and the 'low hydraulic pressure' light illuminated. We reviewed the abnormal checklist and discussed options. I decided to make a precautionary landing at lnk, 100 mi ahead, where there was a 12900' runway and an light transport service center at FBO. During descent hydraulic pressure continued to deteriorate. 10 mi from lnk flaps were selected to 20 degrees and pressure fell to 300 psi. We attempted to lower the landing gear via the normal system, resulting in both main landing gear down and locked and the nosegear unsafe. The gear blowdown lever was selected and subsequently all gear indicated down and locked. Some pressure was regained after the blowdown and it was used to get the flaps nearly full down. We declared an emergency with lnk approach control and requested crash and rescue equipment. The north 3600' of the 12900' runway 17R was closed for survey, but at our request the full length was made available to us after a short delay. The aircraft touched down on speed 1000' from the threshold of runway 17R at a maximum gross landing weight of 17000#. Thrust reversers and ground spoilers deployed normally and the aircraft tracked straight for approximately 2500'. At that point the aircraft commenced a right drift. Toe brakes were applied with no result. The first officer applied the emergency braking handle as briefed at the captain's command. The aircraft came to its ultimate stop approximately 6500' down the runway about 10' from the right edge. Engines were secured. Post-flight investigation revealed both main landing gear brakes smoking heavily and dripping hydraulic fluid. Hydraulic fluid was pooling noticeably under the right mains. Tires #3 and #4 were deflated and heavily damaged. Tires #1 and #2 showed evidence of heat damage, but retained pressure. There were no flat spots on any tire, and no other damage was evident. FBO was contracted to change the 2 deflated tires on the runway, and the aircraft was removed to their hangar for repair. Two FAA personnel were on hand to investigate the declared emergency. I denied their request for permission to inspect the airplane upon the advice of the manager, flight operations. The following day I was contacted by 2 other FAA personnel with a request for permission to confer with FBO to determine which aircraft components failed. They explained this information is required to complete FAA internal forms required whenever an aircraft declares an emergency. Company maintenance department will complete the investigation of all failed components and submit the required malfunction and defect report to the local FAA office. The FAA personnel stressed they had no issue or interest in crew performance, and that this was purely an administrative follow up to an obvious loss of hydraulic fluid failure. A substantial leak was found in the hydraulic system at the right main landing gear brakes. Further testing determined that 4 psi pressure is present in the brake lines with the gear retracted. It is the opinion of the light transport technical rep at FBO that if the integrity of any one brake puck 'O-ring' seal is compromised, enough fluid may pass through a resettable hydraulic fuse in a sufficient period of time to cause low hydraulic system pressure. With gear down, the flow was noticeably more rapid.

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Original NASA ASRS Text

Title: CPR LTT HYDRAULIC PRESSURE LOSS AT CRUISE ALT. PIC ELECTED TO MAKE A PRECAUTIONARY LNDG AT AN ENROUTE ARPT WHERE THERE WAS AN ACFT TYPE SERVICE CENTER.

Narrative: TWO HRS AFTER TKOF, WHILE IN CRUISE AT FL410, WE NOTICED HYD PRESSURE DROPPING SLOWLY THROUGH 1200 PSI. APPROX 10 MINS LATER PRESSURE HAD DROPPED TO 1000 PSI AND THE 'LOW HYD PRESSURE' LIGHT ILLUMINATED. WE REVIEWED THE ABNORMAL CHKLIST AND DISCUSSED OPTIONS. I DECIDED TO MAKE A PRECAUTIONARY LNDG AT LNK, 100 MI AHEAD, WHERE THERE WAS A 12900' RWY AND AN LTT SVC CENTER AT FBO. DURING DSCNT HYD PRESSURE CONTINUED TO DETERIORATE. 10 MI FROM LNK FLAPS WERE SELECTED TO 20 DEGS AND PRESSURE FELL TO 300 PSI. WE ATTEMPTED TO LOWER THE LNDG GEAR VIA THE NORMAL SYS, RESULTING IN BOTH MAIN LNDG GEAR DOWN AND LOCKED AND THE NOSEGEAR UNSAFE. THE GEAR BLOWDOWN LEVER WAS SELECTED AND SUBSEQUENTLY ALL GEAR INDICATED DOWN AND LOCKED. SOME PRESSURE WAS REGAINED AFTER THE BLOWDOWN AND IT WAS USED TO GET THE FLAPS NEARLY FULL DOWN. WE DECLARED AN EMER WITH LNK APCH CTL AND REQUESTED CRASH AND RESCUE EQUIP. THE N 3600' OF THE 12900' RWY 17R WAS CLOSED FOR SURVEY, BUT AT OUR REQUEST THE FULL LENGTH WAS MADE AVAILABLE TO US AFTER A SHORT DELAY. THE ACFT TOUCHED DOWN ON SPD 1000' FROM THE THRESHOLD OF RWY 17R AT A MAX GROSS LNDG WT OF 17000#. THRUST REVERSERS AND GND SPOILERS DEPLOYED NORMALLY AND THE ACFT TRACKED STRAIGHT FOR APPROX 2500'. AT THAT POINT THE ACFT COMMENCED A RIGHT DRIFT. TOE BRAKES WERE APPLIED WITH NO RESULT. THE F/O APPLIED THE EMER BRAKING HANDLE AS BRIEFED AT THE CAPT'S COMMAND. THE ACFT CAME TO ITS ULTIMATE STOP APPROX 6500' DOWN THE RWY ABOUT 10' FROM THE RIGHT EDGE. ENGS WERE SECURED. POST-FLT INVESTIGATION REVEALED BOTH MAIN LNDG GEAR BRAKES SMOKING HEAVILY AND DRIPPING HYD FLUID. HYD FLUID WAS POOLING NOTICEABLY UNDER THE RIGHT MAINS. TIRES #3 AND #4 WERE DEFLATED AND HEAVILY DAMAGED. TIRES #1 AND #2 SHOWED EVIDENCE OF HEAT DAMAGE, BUT RETAINED PRESSURE. THERE WERE NO FLAT SPOTS ON ANY TIRE, AND NO OTHER DAMAGE WAS EVIDENT. FBO WAS CONTRACTED TO CHANGE THE 2 DEFLATED TIRES ON THE RWY, AND THE ACFT WAS REMOVED TO THEIR HANGAR FOR REPAIR. TWO FAA PERSONNEL WERE ON HAND TO INVESTIGATE THE DECLARED EMER. I DENIED THEIR REQUEST FOR PERMISSION TO INSPECT THE AIRPLANE UPON THE ADVICE OF THE MGR, FLT OPS. THE FOLLOWING DAY I WAS CONTACTED BY 2 OTHER FAA PERSONNEL WITH A REQUEST FOR PERMISSION TO CONFER WITH FBO TO DETERMINE WHICH ACFT COMPONENTS FAILED. THEY EXPLAINED THIS INFO IS REQUIRED TO COMPLETE FAA INTERNAL FORMS REQUIRED WHENEVER AN ACFT DECLARES AN EMER. COMPANY MAINT DEPT WILL COMPLETE THE INVESTIGATION OF ALL FAILED COMPONENTS AND SUBMIT THE REQUIRED MALFUNCTION AND DEFECT RPT TO THE LCL FAA OFFICE. THE FAA PERSONNEL STRESSED THEY HAD NO ISSUE OR INTEREST IN CREW PERFORMANCE, AND THAT THIS WAS PURELY AN ADMINISTRATIVE FOLLOW UP TO AN OBVIOUS LOSS OF HYD FLUID FAILURE. A SUBSTANTIAL LEAK WAS FOUND IN THE HYD SYS AT THE RIGHT MAIN LNDG GEAR BRAKES. FURTHER TESTING DETERMINED THAT 4 PSI PRESSURE IS PRESENT IN THE BRAKE LINES WITH THE GEAR RETRACTED. IT IS THE OPINION OF THE LTT TECHNICAL REP AT FBO THAT IF THE INTEGRITY OF ANY ONE BRAKE PUCK 'O-RING' SEAL IS COMPROMISED, ENOUGH FLUID MAY PASS THROUGH A RESETTABLE HYD FUSE IN A SUFFICIENT PERIOD OF TIME TO CAUSE LOW HYD SYS PRESSURE. WITH GEAR DOWN, THE FLOW WAS NOTICEABLY MORE RAPID.

Data retrieved from NASA's ASRS site as of August 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.