Narrative:

Instructor pilot and student experienced smoke in the cockpit during flight after turning on combustion air heater. Aircraft landed without further incident or injury. It was subsequently discovered that the heater assembly was the wrong part number assembly for the aircraft per the aircraft parts manual. The heater installed was a part number 90d38-1, designed initially for installation in a piper PA34 (seneca). The correct part number for a PA44 (seminole) is a part number 90d38-2. The design difference between the two parts is in the direction of the bevel cut on the exhaust tailpipe. When the standard -1 heater is installed in a PA44, the bevel faces forward, which causes ram air to pressurize the tailpipe and combustion tube. Of course this feature was not known to me, the installer, at the time. Original heater installed in aircraft failed pressure decay test required by AD96-20-07. Replacement heater was ordered verbally (by phone) from company maintenance headquarters without specifying part number. (Note: this is a fleet operation of all the same model and serial number range aircraft. It was not uncommon therefore, to order parts in this manner.) replacement part was received and installed in aircraft (log entry 4/tue/00). Part number was the same as the unit being replaced. Part was presumably from company inventory, with maintenance release forms showing overhaul date and recent pressure decay test. Unit was functional tested in aircraft after installation --operation normal. Aircraft was flown from place of installation (ZZZ) to the WWW area where the incident occurred over a weekend (4/sat/00). The incident was brought to my attention the following monday. Subsequent to this installation and prior to learning of the first incident, another heater was being replaced on a same model aircraft and that heater (old and new) was found to be the wrong part number (-1). This second occurrence was discovered prior to completing the installation only by referencing the associated applicability chart supplied with the new heater. (Heater in the first occurrence was a used serviceable unit.) on inspection of several other same model aircraft, several have the -1 part number heaters installed as original equipment and that the -2 assembly was incorporated in later serial number aircraft. Callback conversation with reporter revealed the following information: the reporter stated the replacement heater ordered was the same part number as the removed unit 90d38-1. The reporter said after the cabin smoke incident and researching the cause of the smoke, it was discovered on the early production run of PA-44 aircraft the PA-34 heater was modified and installed. The reporter stated the modification was a bevel cut in the exhaust tailpipe and combustion tube, but still had the 90d38-1 part number. The installed unit did not have the bevel cut and resulted in smoke in the cabin . The parts catalog lists the piper PA-44-180 heater as a 90d38-2 but was not used at the time the new unit was installed. The reporter said other PA-44 aircraft in the fleet have a combination of -1 and -2 units, depending on aircraft age.

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Original NASA ASRS Text

Title: A PA-44-180 EXPERIENCED SMOKE IN THE CABIN WHEN THE CABIN HEATER WAS OPERATED. CAUSED BY INCORRECT HEATER INSTALLED.

Narrative: INSTRUCTOR PLT AND STUDENT EXPERIENCED SMOKE IN THE COCKPIT DURING FLT AFTER TURNING ON COMBUSTION AIR HEATER. ACFT LANDED WITHOUT FURTHER INCIDENT OR INJURY. IT WAS SUBSEQUENTLY DISCOVERED THAT THE HEATER ASSEMBLY WAS THE WRONG PART NUMBER ASSEMBLY FOR THE ACFT PER THE ACFT PARTS MANUAL. THE HEATER INSTALLED WAS A PART NUMBER 90D38-1, DESIGNED INITIALLY FOR INSTALLATION IN A PIPER PA34 (SENECA). THE CORRECT PART NUMBER FOR A PA44 (SEMINOLE) IS A PART NUMBER 90D38-2. THE DESIGN DIFFERENCE BTWN THE TWO PARTS IS IN THE DIRECTION OF THE BEVEL CUT ON THE EXHAUST TAILPIPE. WHEN THE STANDARD -1 HEATER IS INSTALLED IN A PA44, THE BEVEL FACES FORWARD, WHICH CAUSES RAM AIR TO PRESSURIZE THE TAILPIPE AND COMBUSTION TUBE. OF COURSE THIS FEATURE WAS NOT KNOWN TO ME, THE INSTALLER, AT THE TIME. ORIGINAL HEATER INSTALLED IN ACFT FAILED PRESSURE DECAY TEST REQUIRED BY AD96-20-07. REPLACEMENT HEATER WAS ORDERED VERBALLY (BY PHONE) FROM COMPANY MAINT HEADQUARTERS WITHOUT SPECIFYING PART NUMBER. (NOTE: THIS IS A FLEET OPERATION OF ALL THE SAME MODEL AND SERIAL NUMBER RANGE ACFT. IT WAS NOT UNCOMMON THEREFORE, TO ORDER PARTS IN THIS MANNER.) REPLACEMENT PART WAS RECEIVED AND INSTALLED IN ACFT (LOG ENTRY 4/TUE/00). PART NUMBER WAS THE SAME AS THE UNIT BEING REPLACED. PART WAS PRESUMABLY FROM COMPANY INVENTORY, WITH MAINT RELEASE FORMS SHOWING OVERHAUL DATE AND RECENT PRESSURE DECAY TEST. UNIT WAS FUNCTIONAL TESTED IN ACFT AFTER INSTALLATION --OPERATION NORMAL. ACFT WAS FLOWN FROM PLACE OF INSTALLATION (ZZZ) TO THE WWW AREA WHERE THE INCIDENT OCCURRED OVER A WEEKEND (4/SAT/00). THE INCIDENT WAS BROUGHT TO MY ATTENTION THE FOLLOWING MONDAY. SUBSEQUENT TO THIS INSTALLATION AND PRIOR TO LEARNING OF THE FIRST INCIDENT, ANOTHER HEATER WAS BEING REPLACED ON A SAME MODEL ACFT AND THAT HEATER (OLD AND NEW) WAS FOUND TO BE THE WRONG PART NUMBER (-1). THIS SECOND OCCURRENCE WAS DISCOVERED PRIOR TO COMPLETING THE INSTALLATION ONLY BY REFERENCING THE ASSOCIATED APPLICABILITY CHART SUPPLIED WITH THE NEW HEATER. (HEATER IN THE FIRST OCCURRENCE WAS A USED SERVICEABLE UNIT.) ON INSPECTION OF SEVERAL OTHER SAME MODEL ACFT, SEVERAL HAVE THE -1 PART NUMBER HEATERS INSTALLED AS ORIGINAL EQUIPMENT AND THAT THE -2 ASSEMBLY WAS INCORPORATED IN LATER SERIAL NUMBER ACFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE REPLACEMENT HEATER ORDERED WAS THE SAME PART NUMBER AS THE REMOVED UNIT 90D38-1. THE RPTR SAID AFTER THE CABIN SMOKE INCIDENT AND RESEARCHING THE CAUSE OF THE SMOKE, IT WAS DISCOVERED ON THE EARLY PRODUCTION RUN OF PA-44 ACFT THE PA-34 HEATER WAS MODIFIED AND INSTALLED. THE RPTR STATED THE MODIFICATION WAS A BEVEL CUT IN THE EXHAUST TAILPIPE AND COMBUSTION TUBE, BUT STILL HAD THE 90D38-1 PART NUMBER. THE INSTALLED UNIT DID NOT HAVE THE BEVEL CUT AND RESULTED IN SMOKE IN THE CABIN . THE PARTS CATALOG LISTS THE PIPER PA-44-180 HEATER AS A 90D38-2 BUT WAS NOT USED AT THE TIME THE NEW UNIT WAS INSTALLED. THE RPTR SAID OTHER PA-44 ACFT IN THE FLEET HAVE A COMBINATION OF -1 AND -2 UNITS, DEPENDING ON ACFT AGE.

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.