Two February incidents offer insights
The information you review in pilot's operating handbooks about fires is so terse, it creates the impression that it's a simple subject. Emergency checklists divide the subject neatly into typical subtypes of fires: fire on the ground and fire in the air; electrical fire and fuel fire. Fires of uncertain origin, or fires spreading across the instrument panel, or fires touched off when a passenger inadvertently shorts out an electrical connection--these are wild cards that will put you into instant improvisation mode.
Fighting an in-flight fire is enough of a nerve-jangling thought. So what about the other things a pilot is going to have to do to get down safely? Fire is the ultimate distracter. Unlike routine distractions as a door popping open in flight, fire-flying will take more than mental discipline to stay focused. Can you see and breathe? Can you reach and activate the on-board fire extinguisher? Is there a fire extinguisher on board? Ventilate the cabin or not? Yes, if oxygen is depleted. No, if there's a chance that flames will return. In all cases cut off the fire from its source. That means turning off the fuel for an engine fire, and turning off electrical equipment if the fire is coming from wires or black boxes. If the aircraft itself is on fire, you're out of the book.
Two fires not easily classified that broke out aboard general aviation aircraft are worth study. In one it is a matter of interest to see how investigators reviewed aircraft maintenance, the recording of maintenance, and did testing when seeking the cause of what happened on board a Cessna 172N on February 19, 1999. If you want to give that NTSB accident report a look, they're all in the AOPA Air Safety Foundation's Accident Database.
The event started with a traffic accident on a highway. A news reporter and pilot were circling above the scene in the Cessna 172, about a half-mile off the end of the runway at the El Monte, California, airport. The aircraft had a map light located on the left forward doorpost, controlled by a switch that can be set to three positions: red light, white light, and off. In a departure from previous designs, a fuel line is routed nearby.
The NTSB accident summary explained what happened next. "The pilot was in the right seat and the reporter was in the left seat. The reporter was reaching behind in the back seat area and grabbed the left doorpost with her hand for support. A 'pop' noise was heard. Almost immediately, flames shot out from both sides of the Royalite molding covering the left doorpost at the level of the map light-mounting fixture. The pilot reported that black smoke filled the cockpit. He removed his shirt and attempted to suppress the fire, but was unsuccessful. According to the pilot and the reporter, each time the flames were smothered, they came right back and seemed to grow more intense. The reporter then moved to the back seat to escape the flames. The pilot declared an emergency with the El Monte Air Traffic Control Tower and set up for a downwind landing on Runway 1.
"Both occupants said that during the time interval that the pilot maneuvered the aircraft into alignment with the runway and landed, the flames had progressed down the Royalite doorpost covering and spread to the left side cockpit sidewall upholstery and the left side of the cockpit glareshield/instrument panel. As the airplane was rolling to a stop, the reporter exited the right side door, followed immediately by the pilot." About a minute after the airplane came to a stop, the cockpit was "fully involved in flames."
Was it a fuel fire, an electrical fire, or hybrid? Aircraft design and an airworthiness directive regarding the map light switch and wiring became a prominent focus of the investigation. Unlike previous Cessna 172s, the N model had a fuel line routed through the forward doorpost. "In addition, map lights installed in models prior to the 172N were located at the top of the doorpost in an area with more internal clearance between the wires and the light mounting post," the report observed. Spacers were installed to keep a minimum half-inch distance between any electrical conductors and any "line containing flammable fluids." An airworthiness directive (AD) issued in 1980 and a related manufacturer's service letter pertained to the aircraft. "The pertinent provisions of the AD and service letter directed a visual inspection of the metal fuel line and map light switch located in the left-hand forward doorpost for chafing or arcing, and to provide at least 0.50-inch clearance between the map light switch and the fuel line in accordance with procedures in FAA Advisory Circular 43.13-1A. It also required the installation of a nomex cover (insulator)...over the electrical terminals on the rear of the map light switch."
There was a maintenance item of recent interest. "Interviews with company maintenance personnel disclosed that on February 16, 1999, one of the pilots informed the shop that the map light was inoperative in the accident airplane. "Subsequent maintenance records reviews and interviews established that on February 17, 1999, one of the mechanics removed the Royalite doorpost covering and examined the map light area to try to determine why it was inoperative. The mechanic who performed the work reported that he found the washer for the map light mounting post on the cabin floor, so he reinstalled a washer and a nut on the map light post. He further stated that one of the wires between the map light and the switch was disconnected from the switch terminal and he determined that was the reason for the inoperative light. He reconnected the wire and secured the panel. The mechanic tested the light on the ground, found it to be working, and returned the airplane to service."
Here the investigation's focus narrowed. "The mechanic who performed the map light work was interviewed by Safety Board investigators on two separate occasions; by telephone on February 22 and in person on February 24. During the interviews, the investigators were aware of AD 80-04-08 and Cessna SIL 80-3, but asked non-leading general questions concerning what he observed behind the Royalite covering. The mechanic was asked if he recalled anything being behind the map light switch. He responded that he remembered nothing being behind the switch." However, the report also noted: "During the in-person interview, the mechanic volunteered that he had reviewed the parts manual and AD 80-04-08 after the telephone interview. He stated that he definitely reinstalled the Nomex cover over the rear of the map light switch as depicted in the AD."
This report is educational for an aircraft owner, FBO, or pilot. Research done in conjunction with the probe referred to other cases where fires originated in the left forward doorpost of Cessna 172Ns. The probable cause of this extensively investigated accident was stated as "An in-flight fuel fire in the left forward doorpost due to an electrical arc from an adjacent map light switch puncturing a main fuel feed line. The manufacturer's inadequate design in routing the fuel line in close proximity to electrical arc sources in the doorpost is causal. A factor in the accident is the probable failure of the doorpost internal component configuration to conform to original design specifications due to aircraft aging issues."
On February 25, 2004, a 39,700-hour commercial pilot flying a retractable-gear Cessna R182 Skylane was in cruise flight near Elberfeld, Indiana, when he thought he smelled smoke. "I first felt a profound heat sensation on my left shin, and then noticed a pronounced plume of smoke wafting from beneath the left side instrument panel.... I observed a small flame emitting from the electrical wiring bundle where it penetrates the engine firewall above the heater/defroster plenum near the outboard left edge of the firewall. I pushed my seat back fully and discharged the extinguisher towards the flame. The extinguisher agent immediately dispatched the flame, but also eliminated any forward visibility out of the cockpit.
"I opened the right door window and slipped the airplane to the left which caused a net airflow across the cockpit, flushing out enough of the white cloud to allow me to see (and breathe) again. The engine continued operating normally during this event and I observed normal engine instrument indications (fuel pressure, manifold pressure, oil pressure, rpm, and temperatures). I made a hard turn towards the airport (about 9 miles away) and initiated an emergency call to the airport but aborted the call as an overwhelming cloud of acrid black smoke suddenly filled the cockpit making it, again, impossible to breathe or to see straight ahead. My plan immediately became to land the airplane as soon as possible."
By now the pilot had his head out to the window to breathe and find a place to land. "I realized that there was flame and black smoke coming from the left side of the engine cowling at about the level of the carburetor air inlet. I then slipped the plane to the right to attempt to shift the flame away from my window and to avoid a farmhouse." Continuing to maneuver in slips to dodge smoke, he realized that making the landing place he had chosen in a field would require adding power--and that's when he discovered that the engine had failed. "I then rolled out on a heading that was my best guess as to be in alignment with the length of the field and started a flare. I elected to leave the landing gear up and touched down in the plowed field.... The aircraft skidded briefly straight ahead without bouncing, then stopped." He kicked the already-sprung right side door open and crawled out to safety. The aircraft was so severely burned that no testing or inspection could be done on its engine components. The probable cause was left to conclude that the in-flight and on-ground fires occurred "for undetermined reasons."
On-board fires don't command a lot of space in operating handbooks and or get much attention during training, perhaps in part because they're rare occurrences, but dealing with one will call on your best judgment and skills. Still, there are things you can do to get an advantage: have necessary equipment on board, keep tabs on possible emergency landing sites, and know what helped other pilots bring a flaming aircraft quickly and safely back to earth.
Dan Namowitz is an aviation writer and flight instructor. A pilot since 1985 and an instructor since 1990, he resides in Maine.
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