SP AVIATION, INC.

APPROXIMATELY ONE HOUR INTO THE FLIGHT & WITHOUT WARNING CREW EXPERIENCED A VERY LOUD, FULL VOL STATIC SQUELCH COMING THROUGH THE OVERHEAD SPEAKERS. AFTER SWITCHING FROM COMM 2 TO COMM 1 THE SQUELCH NOISE WENT AWAY BRIEFLY. HOWEVER, IT CAME BACK A FEW SECONDS LATER. SWITCHED FREQUENCIES TO 121.5 TO VERIFY IT WASN'T JUST A BAD ATC FREQUENCY OR RECEPTION AREA. ATTEMPTED TO REESTABLISH CONTACT WITH ATC ON COMM 3, BUT AS SOON AS THE YOKE MOUNTED TRANSMIT BUTTON WAS PRESSED, THE SQUELCH NOISE RESUMED. CREW AGAIN ATTEMPTED TO CONTACT ATC ON 121.5, BUT STILL GOT THE LOUD SQUELCH NOISE. THE NOISE BECAME PROGRESSIVELY WORSE AS THE FLIGHT CONTINUED. IT FINALLY BECAME NECESSARY TO DESELECT ALL COMMS, BECAUSE THE SQUELCH NOISE BECAME CONTINUOUS, EVEN WITHOUT DEPRESSING EITHER THE YOKE MOUNTED MICROPHONE TRANSMIT BUTTON OR THE HANDHELD MICROPHONE TRANSMIT BUTTON. WE REALIZED WE WERE IN A TOTAL COMM FAILURE SITUATION, SQUAWKED 7600 & MADE AN UNSCHEDULED LANDING. UPON INITIAL INVESTIGATION IT WAS DETERMINED THAT BOTH NETWORK INTERFACE MODULES, NIM 1 & NIM 2, WERE SUSPECT OF CAUSING THE COMM FAILURE. FURTHER INVESTIGATION IS UNDERWAY & RESULTS WILL BE PROVIDED AS THEY BECOME AVAILABLE.

DUCT OVERHEAT LIGHT ON DURING CRUISE, EMERGENCY PRESSURIZATION LIGHT FLICKERING, CABIN ALTITUDE 5000 AGL. TROUBLESHOT AND FOUND FAILURE OF TORQUE MOTOR TEMPERATURE CONTROL VALVE, LEAR IPC CHAP 21-64-10, FIG 10, ITEM 3, SOLENOID.

CREW REPORT: "COMBINED HYDRAULIC SYSTEM LOSS OF FLUID WHILE AT CRUISE FLIGHT". INSPECTION REVEALED LEAK AT FLIGHT SHUTOFF VALVE "TEE" FITTING. O-RING REPLACED IN FITTING RESOLVING LEAK. AIRCRAFT RETURNED TO SERVICE WITH NO FURTHER PROBLEMS.

CREW EXPERIENCED SMOKE IN THE CABIN CLIMBING THROUGH 25,000FT ON A FLIGHT FROM HWD-HOU. CREW IMMEDIATELY LEVELED THE AIRCRAFT OFF AT 25,500FT. PERFORMED EMERGENCY PROCEDURE AND MEMORY ITEMS FOLLOWED BY CHECKLIST PROCEDURE FOR SMOKE IN THE CABIN, EMERGENCY DESCENT, AND NORMAL CHECKLIST. CREW DECLARED AN EMERGENCY AND RETURNED TO SAN JOSE.

SHORTLY AFTER TAKEOFF, THERE WAS A SLIGHT ODOR OF OIL FROM THE PRESSURIZATION SYS. PASSING 10,000 FT. SMOKE WAS EVIDENT IN THE CABIN AND COCKPIT. THEY LEVELED OFF AT 13,000 FT. AND ELECTED TO RETURN TO DEPARTURE. ON THE DESCENT WITH POWER BACK THE SMOKE STARTED TO CLEAR. THEN THE RT ENGINE THRUST REVERSER UNLOCK LIGHT AND AMBER ENG COMPUTER LIGHTS ILLUMINATED. WITH THE CHECKLIST ALREADY OUT THE CREW LOOKED FOR THE TR AND ENG COMP TABS, AT WHICH POINT THE LIGHTS EXTINGUISHED. DESCENT AND LANDING CHECKS WERE COMPLETED. A SMOOTH AND SOFT LANDING WAS MADE.

NR 3 CYLINDER OFF ENGINE. ALL 8 CLY HOLD DOWN STUDS BROKE, ROD OFF CRACKSHAFT. FLIGHT OK TIL TURN TO DOWN WIND TO LAND, ENGINE FAILED AND AIRCRAFT LANDED SAFELY.

ALL POSITIONS EXCEPT REARMOSTFOLLOWING EMERG LANDING, ENG TEARDOWN REVEALED ALL BUT ONE OF THE TAPPET FACES BROKEN. ENG STILL FUNCTIONING, BUT OIL PRESS WAS VERY LOW AT SHUTDOWN SINCE THE COURSE OIL SCREEN WAS 2/3 FULL OF PEA-SIZED AND SMALLER PIECES OF TAPPET BODY FACES WHICH HAD BEEN BROKEN OFF LIKE WEDGES OF A PIE. ENG TIME SMOH: 995 HRS. TT: 4,968 HRS. POSSIBLE CAUSE WAS ONE BROKEN TAPPET BODY FACE WHICH WAS KICKED BY SPINNING CRANK AND WEDGED BEHIND ANOTHER RECEDING TAPPET BODY AND SOON THROUGH THE ENGINE. CASE BROKEN OUTWARD IN 3 PLACES WHERE PRESS WOULD HAVE BEEN APPLIED BY SOMETHING WEDGED BEHIND A TAPPED BODYFACE. MAGNAFLUX INSP OF REWORKED TAPPETS SHOULD PREVENT THIS.