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)