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On January 21, 1998, at 2123 eastern standard time, an Aerospatiale ATR-42-320, N15827, operated by Continental Express as Flight 3332, was substantially damaged during an engine fire after landing at Bradley International Airport, Windsor Locks, Connecticut. There were no injuries to the 2 certificated pilots, or 36 passengers. The flight attendant received minor injuries. Visual meteorological conditions prevailed for the scheduled flight, which originated from Newark, New Jersey, about 2045. Flight 3332 was operated on an instrument flight rules (IFR) flight plan, and was conducted under 14 CFR Part 121.
In a written statement, the captain reported:
"...Upon touchdown [the first officer]...brought the power levers back to the REVERSE position to slow the aircraft, at which time we both heard a loud bang noise from the right side of the aircraft, and noticed a bright orange glow on the ground outside. As we slowed I heard several secondary bangs coming from the right side of the aircraft, and continued to see the orange glow. We stopped the aircraft on the runway and set the parking brake at which time we received a warning from the panel advising that engine #2 was on fire. This was the first time that the warning sounded. We received no fire warning upon landing or throughout the rollout up to this point. At this time I brought the power levers to Ground Idle as [the first officer]...brought the condition levers back to the FUEL SHUT OFF position. [The first officer]...pulled the number two-engine fire handle and I pulled the number one engine fire handle. [The first officer]...then discharged the squibs for engine number two in an attempt to extinguish the fire. The fire did not go out as a result of this effort. At this time [the first officer]...exited the cockpit to assist with the evacuation as I called for the evacuation to the left side of the aircraft. I continued securing the cockpit. After the cockpit was secured, I exited the cockpit and passed through the cabin ensuring that all passengers had exited the aircraft. I followed the Flight Attendant out the rear main cabin door, and advised all of the passengers to leave the area and head toward the terminal and away from the aircraft. Through the evacuation, the right side of the aircraft continued to burn, as well as a pool of jet fuel that had spilled out of engine number 2...."
The flight attendant in the rear of the airplane opened the left side main cabin door and commenced evacuating the passengers. Smoke started to fill the cabin. A non-revenue company pilot, seated in the forward left side seat, opened the forward left side fuselage emergency exit. He exited the airplane and then assisted passengers as they exited. The first officer exited via the left side emergency exit, and the captain who was last out of the airplane exited through the main cabin door.
The fire was extinguished by airport firefighters.
The accident occurred during the hours of darkness at 41 degrees, 56 minutes north latitude, and 72 degrees, 41 minutes west longitude.
The airplane was equipped with a cockpit voice recorder (CVR) and digital flight data recorder (DFDR). Both units were removed and forwarded to the Safety Board Laboratory in Washington, DC for evaluation. The cockpit voice recorder did not provide any information that was not obtainable elsewhere and a transcript was not prepared. The flight data recorder was examined and report prepared.
WRECKAGE AND IMPACT INFORMATION
Examination of the right engine area disclosed fire damage to the right engine cowling, and to the right trailing edge wing and wing flap. The wing flaps were set at 30 degrees. Several wires along the aft spar were burned, and examination of the rear spar revealed it had been warped about 1/8 inch.
The airplane was equipped with two Pratt & Whitney of Canada (PWC) PW121 series engines. A fuel/oil heat exchanger was located on the left side of each engine, about halfway back from the nose. A fuel filter was part of the heat exchanger. On the right engine, one of three studs used to hold the nuts that secure the filter cover to the heat exchanger was pulled out, and the filter housing was bent away from its fitting about 1/2 inch. The remaining two studs were found to be partially extracted from their holes. The inside of the filter housing, which contained fuel, was exposed.
The pilots reported that they were not aware of a fire until after touchdown. Examination of the engine revealed that, in the area of the fuel leak, there were no fire detectors. However, there was ambient air flow through that portion of the engine, and it exited around the exhaust stack on the engine.
TESTS AND RESEARCH
A Safety Board Powerplants Group was appointed to assist in the investigation. According to the Chairman's report:
"...The disassembly and inspection of the fuel heater assembly commenced in the presence of the Powerplant Group on February 2, 1998. The top several threads in the hole where the stud disengaged were completely destroyed. The two other filter cover studs were found partially disengaged in the housing but were bent. All three filter cover stud holes showed indications that the studs were cross-threaded into the holes....."
Examination of the holes (lugs) that the studs fit into revealed:
"...The top three or four threads were heavily damaged and almost nonexistent, the next thread or two with less damage and remaining bottom threads with no damage. The lug cross-sections and polymer molds exhibited extraneous thread marks that were offset from the tapped threads...."
The fuel heater was manufactured by Steward, Warner and carried a part number of 10718D/AF. The serial number was 510. The unit had accumulated 14,615.8 hours and 18,104 cycles since new. Continental Express used a 1,200 hour check interval, and a 6,600 hours overhaul interval. Prior overhaul records were not required to be kept and were not available for review. Following the overhaul by Kansas Aviation of Independence, on July 30, 1997, the unit was returned to Continental Express and subsequently placed on the engine as a unit on August 27, 1997. Continental Express had no record of removing, servicing or performing any maintenance on the unit since its installation. The unit had accumulated 1,004.7 hours and 1,084 cycles since installation, and was scheduled to be checked when it reached 1,200 hours time in service.
Material was found in the threads of the stud that had pulled out. The material was analyzed and found to be consistent with the aluminum base alloy used for the housing, and the stud. Examination of the stud hole revealed it was oversized. However, exact hole measurements could not be taken due to hole damage. A no-go gage could be partially inserted in the holes.
Testing performed at PWC found that stainless steel 303 studs would shear at 125 inch-pounds, and the studs made from the stronger A-286 material would shear at 250 inch-pounds. In the testing, the studs sheared, but did not pull out of the housing.
The maximum fuel pressure inside the housing was 50 psi. The force required to pull out the three studs was calculated at 13,653 pounds.
Examination of the Steward Warner Component Maintenance Manual revealed following:
1. - No requirements for inspecting the studs for straightness. 2. - No information as to whether a stud would be removed if it were bent, with no other physical damage noted to the housing or stud. 3. - The stud replacement repair procedures, gave a general technique for the removal of studs, but did not provide specific details such as; drill size, drill depth, or the use of drill guides. 4 - There were no notes, cautions or warning that damage to the housing threads were not repairable and when the housing was to scrapped. 5 - No final inspection was specified after a repair, such as a torque check for the proper engagement of the stud with the housing and whether the stud was straight.
The investigation revealed that the fire occurred initially in an area not protected by fire detectors. In addition, there was an ambient air flow in the area of the fuel spill from front to rear, due to forward motion of the airplane through the air, and propeller air flow.
There were two fuel shutoffs. An airframe shut off actuated by the fire handle in the overhead panel, and a shutoff in the hydromechanical fuel control unit which was actuated by retarding the propeller condition levers on the center pedestal to the FUEL SHUTOFF position. The location of the ruptured fuel filter cover was between the two fuel shutoffs.
According to the EMERGENCY EVACUATION checklist, the immediate actions items are:
After the aircraft comes to a stop: Parking Brake SET Condition Levers FUEL SHUTOFF Fire Handles PULL Agents AS REQUIRED
Note: For an engine fire on the ground, it is not necessary to wait 10 second before discharging the fire extinguishing agents. Both agents will be discharged to the engine with the fire indications.
PA "EVACUATE! EVACUATE!" (Directions) Min Cabin Lights ON Tower/Ground (VHF-1) NOTIFIED Fuel Pumps OFF Batteries (Before leaving Aircraft) OFF
Additional Persons participating in this investigation
Mr. Accident Investigation Pratt & Whitney - Canada Longueuil, Quebec
Alain Bouillard Bureau Enquetes-Accidents Le Bourget, France
Robert Graham Stewart Warner, South Wind Corporation Indianapolis, Indiana