Narrative:

On an emergency medical service far part 135 flight to pick up an injured person at XA30 hours, nov/xa/99, an engine #2 chip light illuminated while descending for landing. WX at nearby airport reported clear, mist and 2 mi visibility. The approach was in extreme darkness in hilly terrain while the aircraft was hovering out of ground effect. The zapper pulsed chip detection/system did not extinguish the #2 engine chip light after using it the allowed 3 times. With the darkness, high terrain and restr to visibility combined with extreme blowing dust and dirt from rotor wash (brown out) a landing could not be made. Climb out to clrer WX and visibility was made. With restr to visibility in the ZZZ area due to haze and mist I elected to continue flight to ZZZ where we had departed and visibility was 6 mi. The mechanic inspected the magnetic chip plugs, found an insignificant specification on 1 plug and returned the aircraft to service. On review of the flight manual and supplement for the zapper, I discovered the correct procedure should have been to secure and shut down the #2 engine if '1 engine inoperative' were possible and land as soon as practicable. If 1 engine inoperative was not possible, the flight manual states land as soon as possible. There was no other anomalous engine or performance indications. There was confusion in my mind about the necessity of shutting the engine down with no other supporting indications after the 'zapper' failed to extinguish the light. A landing at the unimproved and unsafe landing area was not possible as was single engine flight while at a high out of ground effect hover. With my uncertainty to the verbiage between the flight manual supplement and the flight manual and the restr to visibility at lower altitudes, I elected to continue with both engines running to a destination (33 NM) with favorable WX. I monitored the performance of the #2 engine closely and was prepared to perform an emergency engine shutdown should one be required. Although at this point I was undecided that an engine shutdown was indicated, even without other supporting data aside from the chip light, I interpreted either land as soon as possible or land as soon as practicable to continue. I did not want to descend into restr visibility and possible SVFR conditions with a possible engine problem and certainly did not want to be there with 1 engine secured. In retrospect, even though in seeming conflict with the flight manual, I do not like the options: land as soon as possible -- fly an aircraft that seemed to be operating all right but with an engine chip light into restr visibility and land in a conurbated area in hilly terrain, or secure an engine and fly over an urban area with hilly terrain to shoot an instrument or SVFR approach, single engine. In reading and rereading the pertinent section of the flight manual, it is ambiguous in wording and intent as to exactly which is the correct emergency procedure to be used for an engine chip light without other substantiating data or indications. Callback conversation with reporter revealed the following information: the reporter stated the engine has operated normally since this incident. The company this individual works for concurs with his judgement call of returning to the departure airport.

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Original NASA ASRS Text

Title: A HELI PLT HAD AN ENG #2 CHIP DETECTOR LIGHT ILLUMINATE INFLT AND RETURNED TO THE DEP POINT FOR A LNDG.

Narrative: ON AN EMER MEDICAL SVC FAR PART 135 FLT TO PICK UP AN INJURED PERSON AT XA30 HRS, NOV/XA/99, AN ENG #2 CHIP LIGHT ILLUMINATED WHILE DSNDING FOR LNDG. WX AT NEARBY ARPT RPTED CLR, MIST AND 2 MI VISIBILITY. THE APCH WAS IN EXTREME DARKNESS IN HILLY TERRAIN WHILE THE ACFT WAS HOVERING OUT OF GND EFFECT. THE ZAPPER PULSED CHIP DETECTION/SYS DID NOT EXTINGUISH THE #2 ENG CHIP LIGHT AFTER USING IT THE ALLOWED 3 TIMES. WITH THE DARKNESS, HIGH TERRAIN AND RESTR TO VISIBILITY COMBINED WITH EXTREME BLOWING DUST AND DIRT FROM ROTOR WASH (BROWN OUT) A LNDG COULD NOT BE MADE. CLBOUT TO CLRER WX AND VISIBILITY WAS MADE. WITH RESTR TO VISIBILITY IN THE ZZZ AREA DUE TO HAZE AND MIST I ELECTED TO CONTINUE FLT TO ZZZ WHERE WE HAD DEPARTED AND VISIBILITY WAS 6 MI. THE MECH INSPECTED THE MAGNETIC CHIP PLUGS, FOUND AN INSIGNIFICANT SPEC ON 1 PLUG AND RETURNED THE ACFT TO SVC. ON REVIEW OF THE FLT MANUAL AND SUPPLEMENT FOR THE ZAPPER, I DISCOVERED THE CORRECT PROC SHOULD HAVE BEEN TO SECURE AND SHUT DOWN THE #2 ENG IF '1 ENG INOP' WERE POSSIBLE AND LAND AS SOON AS PRACTICABLE. IF 1 ENG INOP WAS NOT POSSIBLE, THE FLT MANUAL STATES LAND ASAP. THERE WAS NO OTHER ANOMALOUS ENG OR PERFORMANCE INDICATIONS. THERE WAS CONFUSION IN MY MIND ABOUT THE NECESSITY OF SHUTTING THE ENG DOWN WITH NO OTHER SUPPORTING INDICATIONS AFTER THE 'ZAPPER' FAILED TO EXTINGUISH THE LIGHT. A LNDG AT THE UNIMPROVED AND UNSAFE LNDG AREA WAS NOT POSSIBLE AS WAS SINGLE ENG FLT WHILE AT A HIGH OUT OF GND EFFECT HOVER. WITH MY UNCERTAINTY TO THE VERBIAGE BTWN THE FLT MANUAL SUPPLEMENT AND THE FLT MANUAL AND THE RESTR TO VISIBILITY AT LOWER ALTS, I ELECTED TO CONTINUE WITH BOTH ENGS RUNNING TO A DEST (33 NM) WITH FAVORABLE WX. I MONITORED THE PERFORMANCE OF THE #2 ENG CLOSELY AND WAS PREPARED TO PERFORM AN EMER ENG SHUTDOWN SHOULD ONE BE REQUIRED. ALTHOUGH AT THIS POINT I WAS UNDECIDED THAT AN ENG SHUTDOWN WAS INDICATED, EVEN WITHOUT OTHER SUPPORTING DATA ASIDE FROM THE CHIP LIGHT, I INTERPED EITHER LAND ASAP OR LAND AS SOON AS PRACTICABLE TO CONTINUE. I DID NOT WANT TO DSND INTO RESTR VISIBILITY AND POSSIBLE SVFR CONDITIONS WITH A POSSIBLE ENG PROB AND CERTAINLY DID NOT WANT TO BE THERE WITH 1 ENG SECURED. IN RETROSPECT, EVEN THOUGH IN SEEMING CONFLICT WITH THE FLT MANUAL, I DO NOT LIKE THE OPTIONS: LAND ASAP -- FLY AN ACFT THAT SEEMED TO BE OPERATING ALL RIGHT BUT WITH AN ENG CHIP LIGHT INTO RESTR VISIBILITY AND LAND IN A CONURBATED AREA IN HILLY TERRAIN, OR SECURE AN ENG AND FLY OVER AN URBAN AREA WITH HILLY TERRAIN TO SHOOT AN INST OR SVFR APCH, SINGLE ENG. IN READING AND REREADING THE PERTINENT SECTION OF THE FLT MANUAL, IT IS AMBIGUOUS IN WORDING AND INTENT AS TO EXACTLY WHICH IS THE CORRECT EMER PROC TO BE USED FOR AN ENG CHIP LIGHT WITHOUT OTHER SUBSTANTIATING DATA OR INDICATIONS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ENG HAS OPERATED NORMALLY SINCE THIS INCIDENT. THE COMPANY THIS INDIVIDUAL WORKS FOR CONCURS WITH HIS JUDGEMENT CALL OF RETURNING TO THE DEP ARPT.

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.