According to a search of NTSB data, in 2010, there were only four general aviation fixed-wing accidents investigated that involved in-flight engine compartment fires. That's a representative annual number. Initiating events commonly include things such as fatigue failure of cylinder fuel lines, leaking fittings and deteriorating hoses that should have been removed from service.
There are many opportunities to feed fires in engine compartments where you'll find hoses and lines full of fuel, oil and hydraulic fluid. The FAA has two terms to describe the flammability performance level of materials used in engine compartments: fireproof and fire-resistant.
Fireproof means that a material or component has been tested to withstand a flame of 2,000 degrees F, plus or minus 150 degrees, for a minimum of 15 minutes, and still be able to fulfill its design purpose. Materials or parts used to confine fires to designated fire zones, such as the firewall of an engine compartment, must be fireproof.
Fire-resistant is applied to lines carrying fluids, components like hose fittings, wiring, air ducts, and powerplant controls. Fire-resistant means that the component can perform its intended function under the heat and flame likely to occur at the particular location where it is installed for a minimum of five minutes when exposed to a flame of 2,000 degrees F, plus or minus 150 degrees.
Whether the FAA-prescribed protection is enough to assure survival depends, in large measure, on how quickly a fire is discovered by the pilot so that an emergency response can begin. If you're flying along at 7,500 feet and a fire has been burning in the engine compartment for two minutes before you recognize it, you've only got three minutes to get down before the FAA-prescribed time for fire resistance expires. While that doesn't mean that everything is going to fail and create an inferno, it does mean you'll need a hefty descent rate and all the skill and luck you can muster.
The NTSB recently finished its investigation of an in-flight fire that occurred on September 20, 2009. At about 5:50 p.m., a Piper PA-32R-301T crashed in the Everglades, 22 miles west of the Fort Lauderdale Executive Airport (FXE), Fort Lauderdale, Fla. The Part 91 personal flight was on an IFR flight plan in visual conditions. The private pilot and three passengers were killed, and the airplane was destroyed. The flight originated at Gainesville Regional Airport, Gainesville, Fla.
The flight was being handled by Miami Approach Control at 5:45:47, when the pilot issued a "Mayday" call and reported a "fire in the engine." The controller radioed, "Are you going to try and make it to Executive Airport—that's the closest to you, sir." The pilot replied that he had "smoke in the cockpit and we're trying to get to the nearest airport." Radar data revealed that the airplane was on an assigned heading of 110 degrees, at an altitude of 3,800 feet MSL. The airplane subsequently continued on its assigned heading, but a 300-foot descent was noted.
The controller told the pilot that "Pahokee Airport" [Palm Beach County Glades Airport, Pahokee, Fla.] was the closest airport, 24 miles from his location. The controller then asked the pilot if he wanted to go to Pahokee or "get to Exec?" The pilot responded, "We'd like to get to Exec," and added that he thought he still had power, that "we've lost one cylinder..." and "...that we can see some fire coming off the nose," and that the smoke had dissipated in the cockpit. The airplane maintained an altitude of 3,500 feet for a short period of time before descending to 3,400 feet.
At 5:47:02, the controller radioed that FXE was 24 miles away, and asked the pilot if he still wanted to try to continue to FXE. The pilot advised the controller that he was going to try to continue FXE, and about 40 seconds later, added that he wanted a "visual straight to the runway." Radar data indicated that the airplane was at an altitude of 3,400 feet.
At 5:48:12, the controller directed a heading of "one one zero...vectors straight in for runway eight" at FXE for a visual approach. Radar data indicated the airplane was at 3,300 feet. The controller then advised the pilot that he was going to keep him at 3,000 feet; just in case he had another problem, he would be able to glide to the airport. The pilot acknowledged.
At 5:49:08, the controller advised the pilot that if he felt comfortable, the controller would switch the pilot to a discreet frequency so that he could be worked by "just one" controller, "Can you do that?" When the pilot acknowledged with the airplane's call sign, the controller provided him the new frequency, and stated that the new controller "knows the situation."
At 5:49:40, the new controller acknowledged the pilot's heading, and informed the pilot that "Boca (Boca Raton, Fla.,) is about the same distance, so whichever one you like; twelve o'clock and 25 for executive."
At 5:49:52, the pilot advised the controller that "we're getting more smoke in the cockpit, we're thinking we might have to land on runway (unintelligible) highway two seven here." Radar data indicated the airplane was at an altitude of 2,900 feet.
The controller acknowledged the pilot's transmission and requested confirmation of the pilot's decision to land on highway 27, to which the pilot responded, "Yes, yes." The controller then requested the number of souls on board the airplane. Radar data indicated the airplane was at an altitude of 2,700 feet.
At 5:50:31, the pilot radioed, "We're on fire, we're on fire." There were no further transmissions from the pilot.
A Florida Wildlife Conservation officer told investigators he saw the airplane to the north about 75 feet above power transmissions lines about 1⁄2 mile in front of him. The nose of the airplane was approximately 20 degrees below the horizon, and the airplane was in a 40-degree left bank. The airplane was trailing black smoke, extending back about 100 yards. Visible flames could be seen on top of the engine cowling, extending back toward the cockpit about three feet. The flames closest to the cowling were blue, and the flames toward the cockpit were orange. The trailing black smoke was "like the exhaust of an 18-wheel diesel truck." The bank angle continued to increase and the nose continued to lower until the airplane collided with the ground in a near-vertical attitude.
The pilot, age 46, was rated for airplane single-engine land, and instrument airplane. His FAA third-class medical certificate had no limitations. The pilot reported 2,000 flight hours on his last medical application. The pilot's logbook was destroyed in the accident. According to an insurance application about four months before the accident, the pilot reported 1,883 total hours with 1,183 in the PA-32R.
The six-seat, low-wing, retractable-gear airplane was manufactured in 1985. The engine was overhauled in 1994, and had accumulated 2,030 hours since overhaul. The engine manufacturer recommended that the engine be overhauled after 1,800 hours of time in service or 12 years. Total time at the last annual inspection, in February, 2009, was 3,590.1 hours. The tachometer wasn't located in the wreckage.
The airplane came to rest inverted in approximately six feet of water about 22 nm west of FXE, and on a heading of 258 degrees magnetic. The forward and rear cabin areas were fragmented. The instrument panel was fragmented and the flight instruments, gauges and avionics were not located. Fire damage was extensive.
Examination of the engine compartment revealed localized fire damage on the rear right section of the engine, in the vicinity of the
No. 5 cylinder. Thermal damage was noted on the top section of the engine cowling and around the right side air-intake louvers. The fire was further isolated to the rear right section of the engine, in the vicinity of the turbocharger. The manifold fuel line supplying pressurized fuel to the fuel injector of the No. 5 cylinder, which was located under the turbocharger, was fractured at the fuel injection nozzle. The fractured No. 5 fuel line was sent to the NTSB Materials Laboratory for further examination. Evidence was found of fatigue cracking.
The Pilot's Operating Handbook contains instructions for handling an in-flight fire. It says to switch the fuel selector off, close the throttle, pull the mixture to idle cut-off, turn the fuel pump off, turn off the heater and defroster, turn off the master switch, and land immediately. The FAA says, "By the time a pilot becomes aware of an in-flight engine compartment fire, it usually is well developed...the first step should be to shut off the fuel supply to the engine." The FAA notes that pilots must bear in mind that airplane control can be lost at any moment, and the only thing that matters is the safety of the occupants.
The NTSB determined that the probable cause of this accident was fatigue failure of the No. 5 engine cylinder fuel supply line, which resulted in an engine compartment fire. Also causal was the pilot's failure to immediately secure the engine/perform a forced landing after discovery of the fire, which resulted in the pilot's loss of control of the airplane.
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, write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, NY 10602-0831.