IN-FLIGHT SMOKE ? PROBABLE CAUSE WITH RECOMMENDATIONS
PROBABLE CAUSE WITH RECOMMENDATIONS
NOTE: This PROBABLE CAUSE is SPECULATION . . . a definitive cause of this incident based on detailed technical analysis is UNKNOWN.
PROBABLE CAUSE (Automotive Alternator Regulator Failure):
The most likely probable cause of this in-flight smoke incident is alternator voltage regulator failure and the resultant direct application of extreme overvoltage and excessive amperage to the EarthX battery which was above the highest levels of the stated, rated design of the Battery Management System (BMS) protection and, thus, the battery was forced into thermal runaway; heating up and eventually emitting smoke as it failed.
RECOMMENDATIONS (CORRECTIVE ACTIONS):
1. Install an overvoltage protection system for each aircraft alternator, generator, or dynamo. The authors note that EarthX has amended their operation and installation manual to ?require? overvoltage protection circuitry for alternators exceeding 20 amps of output. The authors agree that overvoltage protection is required.
2. Install the battery?s discreet warning output to either a panel LED or to an EFIS as shown in EarthX?s manual. This installation should also be viewed as required.
3. Install cockpit and/or battery ventilation to expel smoke overboard. The EarthX manual states: ?Installation of the battery in the cockpit is not recommended, unless the battery is properly vented over-board.? Installation of overboard ventilation should be viewed as required.
4. Each EarthX battery and its integrated BMS are extensively tested at the factory before shipment, but field-testing of BMS functionality is not recommended. The authors? understanding from EarthX is that the BMS? overvoltage protection and charging current inhibiting features cannot be successfully field-tested without risking some residual damage to the battery. Thus, installation of overvoltage protection circuitry and the discreet warning output (LED or EFIS) is very important in lieu of being able to safely field-test and measure BMS functionality.
5. If it can be done safely, the aircraft?s overvoltage protection system(s) should be tested after initial installation in the aircraft and then periodically. A sustained overvoltage beyond 16 volts should cause the overvoltage protection system to disconnect the source (alternator) from the aircraft electrical system and battery(s).
6. To protect against smoke emission in the cockpit, fire detection and suppression equipment should be installed if a battery (lithium or lead-acid) is mounted aft of the firewall. This equipment should be readily visible and accessible. For enclosed units like a battery, an injection port would be needed to apply the retardant. From the standpoint of a battery thermal runaway event, the application of fire retardant is most important for the prevention of smoke emission.
7. IMPORTANT: For Non-Builders Purchasing Experimental Aircraft: Make absolutely sure that you have a detailed, current schematic of the aircraft?s electrical system. Carefully analyze the schematic and understand what it means in terms of aircraft electrical system operation, design, redundancy, and safety. Physically inspect the aircraft?s alternator/generating system(s) and aircraft electrical system to confirm that overvoltage protection is installed. Also, if the battery manufacturer supplies a discreet warning output as EarthX does, definitely install it prior to any flight operations.
In summary, it is important to realize that if you purchase an experimental aircraft built or modified by someone else, you effectively become the aircraft?s engineer and design decision maker; not just its pilot, owner, and maintainer. Buying an experimental aircraft is not like buying an FAA-certified aircraft whose design/build is formally reviewed, tested, and controlled. For an experimental aircraft, you must make sure that the aircraft?s systems are acceptable to you based on your own design, cost, and flight risk decisions; not the builder?s or modifier?s. If you do not feel confident in your ability to properly assess an experimental aircraft?s design, definitely find a respected, experienced aircraft builder to help you determine the aircraft?s design, build condition, and relative level of safety. DO NOT TAKE ANYTHING FOR GRANTED or fail to analyze the aircraft?s build quality and systems from a safety standpoint! In other words:
FLY KNOWLEDGEABLE AND FLY SAFE!