NTSB Factual Report

HISTORY OF FLIGHT

On June 8, 2009, about 1143 eastern daylight time, an Iniziative Industrali Italian Sky Arrow 600 Sport special light sport airplane, N445SA, was undamaged following an in-flight electrical smoke event and complete loss of engine power, and a subsequent forced landing near Marietta, Georgia. The certificated flight instructor (CFI) and student pilot were uninjured. The instructional flight was operated under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91. Visual meteorological conditions prevailed for the flight, and no flight plan was filed.

According to the CFI, he and the student departed from runway 27 at Cobb County Airport-McCollum Field (RYY), Marietta, Georgia, on a cross-country check flight for the student. When the airplane was climbing through approximately 2,000 feet above mean sea level, which was approximately 1,000 feet above ground level (agl), both he and the student noticed the smell and appearance of electrical smoke in the cockpit. The smoke was described as being visually "light but perceptible" by the CFI. The CFI took control of the airplane, executed a 180 degree turn back to RYY, notified the RYY air traffic control tower (ATCT) of the situation, and of his intentions to return immediately. ATCT personnel queried whether he was declaring an emergency, and the CFI responded in the affirmative. ATCT personnel then cleared the airplane to land on runway 9, and began rerouting local air traffic that was operating on runway 27.

According to the student pilot, the CFI, seated in the rear seat, and without access to the airplane ignition switch, electrical switches or circuit breakers, asked the student in the front seat to "turn everything off except the radio," which he did. After receiving the ATCT clearance to return to RYY, the CFI asked the student to turn off the radio. The student turned off the radio, and also turned off the master switch. Shortly thereafter, the CFI instructed the student to turn on the master switch and radio, but "they would not work." When the student cycled the master switch to the "OFF" position, and then back to the "ON" position, the engine ceased operation.

According to the CFI, the power loss occurred at an altitude of approximately 800 feet agl. He determined that the airplane would be not be able to reach RYY, and opted to land on a road instead. In his written account, the CFI stated that after "considering emergency landing area options, I elected to exercise PIC [pilot in command] emergency authority and land on Hwy 41 South in the vicinity of Loring Road, Cobb County GA - with only 700 to 800 feet AGL to work with, this seemed the most appropriate course of action. In prioritizing my attention and actions from the point of engine failure to touchdown, and given our low altitude, precarious nature of the emergency landing area, and concern associated with a potential electrical fire, I did not engage in the application of any ancillary emergency procedures outside of managing aircraft energy state and flight path." The landing was uneventful, there was no ensuing fire, and neither the airplane nor any ground objects were damaged.

PERSONNEL INFORMATION

Federal Aviation Administration (FAA) records indicated that the CFI held airline transport pilot, commercial pilot, and flight instructor certificates. His flight instructor certificate had airplane single engine, multiengine, and instrument airplane ratings. He also held a ground instructor certificate with an advanced ground instructor rating. His most recent FAA first-class medical certificate was issued in December 2008, at which time he reported 10,000 total hours of flight experience. The CFI indicated that he had 100 hours of flight experience in the incident airplane make and model, and that his most recent flight review was accomplished in June 2009.

According to the student pilot, he had accumulated approximately 24 total hours of flight experience, all of which were in the incident airplane make and model. The student pilot did not hold an FAA medical certificate; instead he used his valid state-issued driver's license in lieu of a medical certificate, as permitted by 14 CFR 61.303.

AIRPLANE INFORMATION

According to FAA and operator information, the airplane was manufactured in 2007, and was equipped with a Rotax 912 ULS 100 horsepower engine. It had accumulated approximately 339 hours total time in service, and approximately 24 hours since its most recent conditional inspection in April 2009.

The incident airplane was designed, manufactured and operated in accordance with the regulations and standards of the Light Sport Aircraft (LSA) category. LSA category aircraft were not certificated to Federal Aviation Regulations (FAR) Part 23 Airworthiness Standards, but were instead designed and manufactured in accordance with an industry consensus standard. Manufacturers of aircraft slated for airworthiness certification in the LSA category must manufacture the aircraft to the design requirements and quality system of the applicable consensus standard that have been accepted by the FAA, and published through a notice of availability in the Federal Register. To meet the intent of FAR 21.190, and to be eligible for a special airworthiness certificate for LSA category, applicants must present satisfactory evidence that the aircraft was manufactured and was found acceptable to the provisions of the applicable consensus standard. Evidence of acceptability was provided by the LSA manufacturer's statement of compliance, FAA Form 8130-15, attesting to compliance with the requirements of 21.190 of the FAR.

METEOROLOGICAL INFORMATION

The automated weather observation at the departure airport, about the time of the incident, included variable-direction winds at 4 knots, visibility 10 miles, scattered clouds at 2,800 feet agl, broken cloud layer at 5,000 feet agl, temperature 28 degrees C, dew point 17 degrees C, and an altimeter setting of 30.04 inches of mercury.

WRECKAGE AND IMPACT INFORMATION

According to information provided by the FAA inspector who responded to the incident, the landing location was approximately 3.6 miles west-northwest of the departure airport. An FAA airworthiness inspector was also present to examine the airplane. When the master switch was turned "ON", the sound of the battery relay activation was heard as expected, but no power was available to the airplane electrical systems. The master switch was cycled three more times, and the same results were obtained.

The cover for the forward electrical compartment was removed to gain access to the airplane battery and circuit components located forward of the instrument panel. The primary circuit components in this area included relays, terminal junctions, and fuse blocks. A fuse block was an insulated housing which held a removable fuse, and was equipped with terminal accommodations for the associated airplane wiring. The "main bus line fuse," which was electrically situated between the battery and the main bus bar, was located in this compartment, just below the battery relay. The FAA inspector "reset" the fuse by opening and re-closing the cover on the fuse block, and when the master switch was placed in the "ON" position, electrical power was observed on the airplane. The engine was then started; start-up and operation were normal. The magnetos were checked, and they functioned and grounded out normally, which resulted in shutdown of the engine. The engine was re-started, but an over-voltage condition was noted when the fuse block was disturbed by hand, and the engine was then intentionally shut down using the ignition switch. With the master switch still "ON," it was observed that slight finger pressure on the fuse block cover resulted in voltage variations, including a complete electrical power interruption, in the airplane electrical system. The airplane was recovered from the site, and transported to a secure location for additional examination.

ADDITIONAL INFORMATION

Airplane Electrical System

All installed and examined components were confirmed to be those specified by the airplane manufacturer. The airplane was equipped with a 12 volt electrical system and a main bus bar. Electrical power was supplied by a battery and an engine-driven alternator. A master switch enabled electrical power to be provided to the battery relay, starter relay, and the main bus bar. With the exception of the battery and starter relays, all airplane circuitry was enabled and protected via the main bus line fuse.

System voltage was controlled by a voltage regulator. The sense lead for the voltage regulator was connected to a terminal on one side of the main fuse block. Variations in the voltage detected by the sense lead caused the regulator to adjust the system voltage in order to maintain the nominal 12 volt value. System over-voltage values that ranged from 17.2 to 20 volts were observed by the personnel when the main fuse block was manipulated by hand.

Electrical power for the engine ignition system was provided by magnetos, and ignition system operation was independent of the airplane electrical system; once the engine was running, the position of the master switch would not affect engine operation.

The only abnormalities detected during the post-incident examination were with the main fuse block and an avionics cooling fan. No other malfunctioning or damaged components were noted, and the airplane was returned to service shortly after the incident.

Main Fuse Block

The main fuse block was a Ferraz Shawmut model MSC10, designed to hold a 10mm x 38mm fuse rated at 32 amperes. According to the Ferraz Shawmut website, fuse blocks were for circuit protection of equipment in industrial applications. The fuse blocks "have operating handles for non load-break disconnecting and electrical isolation for fuse-link replacement without tools. All contacts are silver-plated. 2, 3 or 4-pole units can be made up with assembly pins and operating handle ties." The fuse blocks featured "screw mount or symmetrical DIN rail mount (with adaptor)" and a "thermoplastic base."

The fuse was retained in the fuse block by a lever-action handle. Fuse installation was accomplished by lifting the handle (to expose the fuse cavity), placing the fuse in the cavity, and then pushing the handle closed so that it was nearly flush with the fuse block body. According to a representative of the airplane manufacturer, the force required to open the handle was 2.4 kilograms, or about 5.3 pounds. However, the fuse block handle, and therefore the fuse itself, was not retained in the closed position by a positive locking mechanism. The fuse block handle was equipped with provisions for installation of lock wire to positively retain the handle and fuse, but at the time of the incident, the airplane manufacturer did not specify the use of lock wire.

According to a representative of the airplane manufacturer, the "fuse holder from Ferraz Shawmut is not an aviation part, we agree on that. But it is a quality product ruggedized and reliable. We are utilizing it since 1995 without a single problem. The metallic fuse holder, located inside, locks the fuse very firmly independently from the plastic hinged protection plastic cover. The cover is designed to install and remove the fuse even in a stack of holders without the help of metallic tools. After having introduced the fuse in the metallic clamps, the cover keeps a limited backlash to guarantee that the fuse is correctly held in place by them."

About 2 months after the incident, the airplane manufacturer issued service guidance to owners and operators that recommended that they verify the installation of the main fuse block and fuse, safety wire the fuse block handle (fuse retainer) in the closed position, and make the appropriate maintenance record entries. According to a representative of the operator, which was also the United States dealer for the incident make and model airplane, under LSA regulations, manufacturers cannot mandate corrective actions unless they address "safety of flight" issues, and the guidance was not mandatory because installation of the safety wire was not considered a safety of flight issue. The airplane manufacturer provided the service guidance to the dealer, who then provided it to all registered owners of the incident airplane make and model. The dealer representative noted that some airplanes had been sold, but not re-registered by the new owners, and therefore those new owners did not necessarily receive the original guidance.

In May 2010, the airplane manufacturer issued a revision (Service Bulletin LSA 3I 01/09, Revision 1) to the previously-issued guidance. The revision differed from the original guidance in two principal ways; it contained the text "RECOMMENDED," highlighted in a red-outlined box at the top of the first page, and it specified a compliance time within which the recommended actions were to be accomplished. In addition, in the manufacturer's communication to the NTSB, they indicated that the incident make and model airplanes were now being produced with main fuse blocks that were safety wired in the closed position.

Avionics Cooling Fan

Examination of the airplane revealed that an avionics cooling fan exhibited melting damage consistent with overheating of the component. No other evidence of overheating or electrical arcing was observed on the airplane. The fan was a magnetic levitating fan manufactured by Sunon, model number KDE1206PTV2. According to the fan manufacturer’s technical information, the normal fan operating parameters were 12 volts, 0.07 amperes, and 3,800 rpm.

The fan was removed and sent to the National Transportation Safety Board (NTSB) materials laboratory for examination. The motor case exhibited a melted penetration that measured approximately 0.25 by 0.5 inches. The case was removed to expose the motor and the fan interior, and the fan printed circuit board (PCB) exhibited thermal damage. Thermal damage was also found on the shaft case and fan spindle adjacent to that area. There was no evidence of arcing on the electrical components on the PCB or on the windings of the motor. The thermal damage was consistent with an excess-current event on the PCB.

According to the operator, after the fuse block and damaged cooling fan were replaced with new units, the incident airplane functioned normally. The electrical problems did not recur, either in the incident airplane, or any other of the operator's airplanes of the same make and model.

NTSB Probable Cause

An electrical fire due to the lack of a positive locking mechanism for the fuse retainer in the main fuse block, which resulted in voltage fluctuations that caused thermal damage to the avionics cooling fan. Contributing to the incident was the student pilot's inadvertent shutdown of the engine at low altitude.