Narrative:

Conditional inspection on aircraft performed. Finished mar/fri/07. Oil sample sent out; normal at this time. Aerwolf filter changed; old unit cut open and inspected for contaminants. None found. Removed and disassembled cuno screens and inspected. No contaminants found. Removed both chip detectors and drain oil from jump and power sections of engine. Both chip detectors tight and seem normal. Reassembled all components and safety. While owner was flying aircraft; he made a precautionary landing due to chip light coming on. I called the customer and was told everything is ok. But the FAA has an investigation towards the owner. We performed all the tasks as per the service manual; but sometimes chip detectors can show erroneous readings. The best thing for the pilot to do if this occurs; is to land as soon as possible and inspect any problems before conducting further flight. Callback conversation with reporter revealed the following information: reporter states this engine has a (3) bladed propeller. The chip detector lights come on in both the fwd and aft cockpit seats. This engine's master rod main bearing had a silver babbitt type material that tends to delaminate and ultimately can clog the engine cuno metal oil filter. Hence; the magnetic chip detectors for early warning of possible bearing failure. Many of these aircraft were built from 1948 era and the chip detector circuitry has deteriorated; causing false signals and illuminating the chip detector lights in the cockpit. This aircraft still has an active chip warning system and that's why the pilot landed as a precaution. No metal was found. Also the aerwolf intake filter is a paper material allowing the mechanic/owner to cut the removed filter to inspect for contaminants.

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Original NASA ASRS Text

Title: A NORTH AMERICAN T-28 ACFT WITH A WRIGHT R-1820-86B ENGINE MADE A PRECAUTIONARY LANDING DUE TO OIL CHIP DETECTOR LIGHTS CAME ON.

Narrative: CONDITIONAL INSPECTION ON ACFT PERFORMED. FINISHED MAR/FRI/07. OIL SAMPLE SENT OUT; NORMAL AT THIS TIME. AERWOLF FILTER CHANGED; OLD UNIT CUT OPEN AND INSPECTED FOR CONTAMINANTS. NONE FOUND. REMOVED AND DISASSEMBLED CUNO SCREENS AND INSPECTED. NO CONTAMINANTS FOUND. REMOVED BOTH CHIP DETECTORS AND DRAIN OIL FROM JUMP AND PWR SECTIONS OF ENG. BOTH CHIP DETECTORS TIGHT AND SEEM NORMAL. REASSEMBLED ALL COMPONENTS AND SAFETY. WHILE OWNER WAS FLYING ACFT; HE MADE A PRECAUTIONARY LNDG DUE TO CHIP LIGHT COMING ON. I CALLED THE CUSTOMER AND WAS TOLD EVERYTHING IS OK. BUT THE FAA HAS AN INVESTIGATION TOWARDS THE OWNER. WE PERFORMED ALL THE TASKS AS PER THE SVC MANUAL; BUT SOMETIMES CHIP DETECTORS CAN SHOW ERRONEOUS READINGS. THE BEST THING FOR THE PLT TO DO IF THIS OCCURS; IS TO LAND ASAP AND INSPECT ANY PROBS BEFORE CONDUCTING FURTHER FLT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATES THIS ENGINE HAS A (3) BLADED PROP. THE CHIP DETECTOR LIGHTS COME ON IN BOTH THE FWD AND AFT COCKPIT SEATS. THIS ENGINE'S MASTER ROD MAIN BEARING HAD A SILVER BABBITT TYPE MATERIAL THAT TENDS TO DELAMINATE AND ULTIMATELY CAN CLOG THE ENGINE CUNO METAL OIL FILTER. HENCE; THE MAGNETIC CHIP DETECTORS FOR EARLY WARNING OF POSSIBLE BEARING FAILURE. MANY OF THESE ACFT WERE BUILT FROM 1948 ERA AND THE CHIP DETECTOR CIRCUITRY HAS DETERIORATED; CAUSING FALSE SIGNALS AND ILLUMINATING THE CHIP DETECTOR LIGHTS IN THE COCKPIT. THIS ACFT STILL HAS AN ACTIVE CHIP WARNING SYSTEM AND THAT'S WHY THE PILOT LANDED AS A PRECAUTION. NO METAL WAS FOUND. ALSO THE AERWOLF INTAKE FILTER IS A PAPER MATERIAL ALLOWING THE MECHANIC/OWNER TO CUT THE REMOVED FILTER TO INSPECT FOR CONTAMINANTS.

Data retrieved from NASA's ASRS site as of January 2009 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.