Fighting The Fire

The risk of in-flight fire is managed through the design of aircraft structures and systems, the type of materials that are used in furnishings, the elimination of accidental sources of ignition, periodic inspections to discover and eliminate hazards before they have a chance to create problems, providing on-board fire-fighting equipment, and training of cockpit and cabin crews. In general aviation (GA), however, pilots may discover that dealing with the risk of an in-flight fire has been put on the back-burner. Few GA pilots receive initial and recurrent fire fighting training and, if there's a fire extinguisher on board an aging GA aircraft, there's a good chance it hasn't been tested or refilled in years.

In August 2011, the National Transporatation Safety Board (NTSB) made a Safety Recommendation suggesting that the FAA update its Advisory Circular (AC) 120-80 "In-Flight Fires." It took until December 2014 for the FAA to release an updated version, circular number AC 120-80A (http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/1026526).

If you're not familiar with it, I highly recommend that you get a copy and study it as if your life depends upon it. It just might. Although aimed at air carrier crews, and dealing primarily with fighting fires on larger aircraft, the circular contains valuable tips that could make a difference if you ever have to deal with a scenario in which fumes, smoke and flames are trying to fill your airplane.

The advisory circular points out that a majority of hidden in-flight fires are the result of electrical arcs along wire bundles. Contamination such as oil or corrosion inhibitors on wiring can promote the spread of flames. Resetting a circuit breaker that has tripped can lead to overheated wiring and arcing. Electrical motors can overheat and possibly ignite surrounding materials. Although very infrequent, lightning strikes have started fires. Rechargeable lithium-ion batteries have a potential for overheating and exploding. There are potential fire sources under the engine cowling, ranging from a broken hose that sprays flammable fluid onto a hot surface to leaking hot exhaust gas. And, let's not forget about malfunctioning gasoline fueled in-cabin heaters.

The advisory circular suggests that your first hint that something bad is happening may come from fumes. The FAA says, "Never ignore a strange odor; you need to identify its source as soon as possible."

If do you detect fumes, smoke or flames, begin the process of executing an emergency landing even as you begin trying to fight the fire. The FAA's Advisory Circular warns, "Delaying descent by only a couple of minutes may make the difference between a successful landing and evacuation and complete loss of the aircraft."

The NTSB recently completed its investigation of an accident in which a piece of auxiliary equipment on a Cessna 172M caught fire, but was out of reach of the airplane's occupants.

On June 27, 2013, the 172M struck powerlines and the ground while the pilot was trying to execute an emergency landing on a road near Birdseye, Utah. The commercial pilot was seriously injured, and the other person on board received fatal injuries. It was VFR for the local flight.

The airplane was owned by a company that made radar equipment used by the U.S. military. Representatives of the company told investigators that the airplane was one of two Cessna 172s used as platforms for the development and testing of the airborne radar systems developed for the Department of Defense. The airplanes were based at Spanish Fork-Springville Airport (U77), Springville, Utah. The company employed one full-time pilot. On the morning of the accident, the company's pilot was operating the other company airplane, so a contract pilot was hired to fly the accident airplane. The mission plan was to fly predetermined tracks around an area about 16 miles south of U77, at an altitude of about 8,000 feet MSL (2,500 feet AGL). It was expected that the flight would last several hours.

There were no problems with engine start, taxi, run-up and takeoff. The airplane arrived on station over Birdseye and conducted the straight-line track portion of the test program, which took about two hours. The pilot then began flying some 360-degree orbits.

After flying several orbits, the test engineer told the pilot that he smelled smoke. The pilot discontinued the orbiting, and began looking for the smoke and its source. He noticed smoke wafting from under the front seats toward the front of the aircraft, and opened both windows and one vent to evacuate the smoke. He then looked over his right shoulder, toward the rear of the airplane, and saw an open flame about eight inches high and four inches in diameter. The flame was situated on top of one of the test equipment components that were located behind the front seats.

The pilot decided they needed to get down fast. He scanned the terrain below and decided that landing on a road was the best option. The pilot turned the airplane northbound with the road on the right. His plan was to fly a rectangular pattern and land to the south. He broadcast a "mayday" on the emergency frequency 121.5. A passing airliner responded almost immediately. The pilot gave the airliner's crew the Cessna's registration number and location, advised they had a fire, and stated his intention to land on the road. The pilot then focused on the landing. Just before the planned touchdown, when the airplane was about 30 feet above the road, the pilot saw a powerline that was suspended above the road and in the airplane's path. He pulled up and tried to overfly it. However, the plane hit the wire, and then other wires, and hit the ground. Passers-by stopped to help, and called emergency services.

The pilot told investigators that the company's equipment test flights always included two people; a pilot and an engineer/observer. The pilot was responsible for flying the airplane to the test area, and executing the designated flight test ground tracks, which were depicted on the panel-mounted guidance equipment. The pilot stated that the engineer/observer generally had the responsibility to either perform or assist with the equipment mounting and hookup, and that specific operations of the equipment were the responsibility of the engineer/observer. On the accident flight, the engineer was an employee of the company. He wasn't a pilot.

There was no fire extinguishing equipment on board, nor was a fire extinguisher required equipment for the flight. When the Cessna was certificated, the FAA didn't require general aviation airplanes to be equipped with a fire extinguisher. That subsequently changed.

In order to provide for the electrical power needs of the various radar systems and support equipment being tested or used on the Cessna airplanes owned by the radar manufacturing company, and also to enable those devices to be electrically isolated from the airplanes' electrical systems, the company designed and built supplemental power supply systems for the airplanes. The rear seats were removed, and the power supply system was placed in the baggage area and the area where the rear seats had been located. The supplemental power supply systems provided 12 volts DC, 28 volts DC and 120 volts AC to the radar and support equipment.

The NTSB's report noted that piston-engine general aviation airplanes are high-vibration environments, and electrical wiring needs to be properly secured to prevent vibration, which could result in damage to its insulation or breakage.

The Safety Board suggested that the supplemental power supply was designed more like testing equipment to be operated in a benign stationary environment with minimal or no vibration, not like a device that was intended for use in a high-vibration environment.

A company technician who built the supplemental power supply installed it in the accident airplane a few weeks before the accident. The technician was not an FAA-certified aircraft mechanic. No guidance or other documentation regarding the physical installation of the system components in the airplane, or the security and protection of the associated wiring was provided by the operator.

The NTSB determined that the probable cause of this accident was the operator's improper installation of a supplemental electrical power supply that caused a short circuit due to inadequate vibration and abrasion protection, which resulted in chafing of the wires, which contacted one another, short circuited, and caused an onboard fire. Contributing to the accident were the installation of the supplemental electrical power supply system without the supervision of an FAA-certified mechanic, the lack of an onboard means for fire suppression, and the pilot's inability to see the power lines across the approach path until it was too late to take evasive action.

Peter Katz is editor and publisher of NTSB Reporter, an independent monthly update on aircraft accident investigations and other news concerning the National Transportation Safety Board. To subscribe, visit www.ntsbreporter.us or write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, N.Y. 10602-0831.