LML Family,
Bill Harrelson and I had a chance to review the
investigation and preliminary causes of an in-flight fire in a Lancair IV-P
that occurred last spring (2009). The findings and conclusions are not yet
established, but the investigator felt that some of the information discovered
was not in question, and would be useful to the experimental community. We
agreed to help spread the word…as follows:
The accident aircraft experienced an in-flight battery fire
of the secondary electrical system shortly after takeoff. The pilot was able to
return to the airport and extinguish the fire in the tail section of the
aircraft after landing. The battery, case, and nearby components were consumed/destroyed,
and the aircraft fuselage sustained significant heat damage from the aft pressure
bulkhead to the elevators/rudder. The cause of the fire has not been absolutely
determined, but the lead/acid battery vents had apparently been obstructed, resulting
in a case rupture and venting of hydrogen gas into the tail section of the
airplane. The exact cause of this apparent over pressurization and rupture awaits
additional information and analysis. This finding and the final NTSB report are
expected within a month and we will disseminate this report through the LML and
LOBO newsletter.
One initial result of the investigation was that the B&C
regulator for the secondary electrical system was inoperative upon post-flight
analysis. The NTSB investigator conducted a detailed examination and analysis
of the defective unit and determined that the electrical design was robust and
appropriate to the task. The unit was mounted to the engine side of the
firewall with the spade terminal connectors projecting to the side of the
aircraft. This unit is not sealed, and at some point liquid (probably water)
entered the metal box, most likely through the opening around the spade
terminals, and filled it to a depth of ¼ to ½ inch. The liquid allowed arcing
among internal components and to the case ground, leaving carbon tracks on the
circuit board and case, and destroying the electrical functionality.
A review of installation instructions provided with B&C
regulators recommends they be installed inside the cockpit or in a similar
environmentally-protected area. This regulator was mounted inside the engine
compartment, as we believe are the vast majority of Lancair installations. When
so installed, regulators are subject to additional heat and cooling stresses,
as well as water/solvents from engine cleaning and other maintenance when the
cowling is removed. If mounted in any position other than with the spades down,
liquid can enter in the area of the spade terminals and will then be trapped
within the lower part of the enclosure, immersing part of the main circuit
board.
If you are still building and have the option, review the
B&C recommendations on mounting location and consider locating your
B&C regulator(s) inside the cockpit; preferably with the spades down if
there is any possibility of liquid exposure. No matter the location, mount them
in such a way that they cannot ingest and retain water.
If you are not able to locate the regulator(s) as
recommended by B&C, consider shielding the terminal strip area from
liquids. We expect to contact B&C about the feasibility of other
improvements that could be made, but will refrain from making any
recommendations until we receive their comments.
Bob Pastusek & Bill Harrelson
For the Lancair Owners & Builders Organization (LOBO)