Date: 201304
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: Rangemaster (Navion)
Operator: Personal
Operating under: Part 91
Mission: Personal
Flight phase: Cruise
Aircraft component: External Power
Reporter organization: Personal
Reporter function: Technician; Inspector
Reporter qualification: Maintenance Inspection Authority; Maintenance Powerplant; Maintenance Airframe
Human factors: Communication Breakdown; Confusion; Situational Awareness; Troubleshooting
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Landing Without Clearance; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor; Inflight Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Aircraft Damaged; Flight Crew Landed in Emergency Condition; General Maintenance Action
Contributing factors: Aircraft; Human Factors; Manuals; Incorrect / Not Installed / Unavailable Part
Primary problem: Aircraft

Narrative: Cabin Air Mixture Valve housing chafed above terminal boot against 'Positive' cable terminal of Aux Power plug. The path to 'Ground' was through actuator cable to instrument panel. Cable subsequently heated up; creating smoke in the cabin from internal lubricants in the cable and a very small area of an adjacent interior side panel. Aircraft in controlled airspace and had to shut-off electrical power; flight continued and landed without further incident at an uncontrolled field. Pilot contacted ATC via landline; no emergency or priority handling by ATC was given.

Callback: Reporter stated the Aux Power cable for External Power hook-up; is always 'Hot' electrically; when the Master switch is in the 'On' position. No Circuit Breaker (C/B) or electrical switching solenoid were designed or installed in the Navion 'G' model in 1962; the year his aircraft was built. The Master switch is the only electrical cut-off for the Aux Power cable. The air volume control for the Air Mix Valve is a Bowden 'Push-Pull' type cable with an outer sheath; both are metal. The 'Push-Pull cable is attached to the Air Mix Valve box and in very close proximity to the Aux Power cable receptacle.  He had to shut off the Master electrical switch when smoke in the cabin occurred; because the metal Air Mix Valve housing had chafed through the protective boot on the 'Positive' terminal stud of the Aux Power receptacle and went to 'Ground' through the Air Mix box housing and the 'Push-Pull cable attach location on the instrument panel.Reporter stated that during his troubleshooting of the cause for the smoke in the Navion's cabin; he could not understand why the Cabin Air Mixture Valve housing; which is in a tight location above the aircraft's Auxiliary (Aux) Power cable; did not have better support.  He could not find any provisions for a Stand-off; or factory pre-drilled holes; in the Engine compartment's structure that would indicate additional support should have been there.  The current Illustrated Parts Catalog (IPC) for the Navion Rangemaster 'G' models does not show any additional support for the Air mixture housing. He could not find any information in the FAA's data base about a Navion Air Mix Valve housing. Reporter stated that over the years; Navion aircraft have had different Type Certificate (T/C) holders. The brace part was available and was installed.   Part-91 Owner/ Operators may not always see Service Bulletins; maybe Airworthiness Directives (A/D); but not necessarily other information about their aircraft. So he filed this NASA ASRS report hoping to alert other owners and operators of the Rangemaster 'G' models about the potential for the Air Mix Valve housing to chafe on the Aux Power cable due to a missing support brace.



Synopsis: An Inspector/Technician reports a metal Cabin Air Mixture Valve housing had chafed through a terminal boot on the 'Positive' cable terminal stud at an Auxiliary Power receptacle creating smoke in the cabin of a Navion Rangemaster 'G' model aircraft. Pilot had to shut off electrical power with Master Switch while in controlled airspace.