Portland, OR, USA
N822PH
de Havilland DHC-8-102
Horizon Air flight 2325, a de Havilland DHC-8-102, on a scheduled 14CFR121 flight sustained an engine fire in a Pratt & Whitney (P&W) PW120A engine while on approach to Portland International airport, Portland, Oregon. An engine examination and teardown determined that the #5 bearing assembly had failed. Additional examination ascertained that the P2.5/P3 switching valve to rear inlet case sealing air tube had become disconnected, and the NL probe port sealing tube had melted, allowing an oil fed fire outside of the engine casing and into the engine compartment. Investigation determined that the engine had not been placed on oil consumption and daily chip detector examination by company maintenance as required by the engine maintenance manual following a loss of oil event approximately 180 hours previous to the fire. Additionally, the mandatory implementation of P&W service bulletin 20914, which addressed the P2.5/P3 switching valve to rear inlet case sealing air tube and NL probe port sealing tube was not carried out by the company, nor was it required, as the FAA airworthiness directive making the service bulletin mandatory did not include the PW120A engine. The investigation also revealed that the company mandated implementation of P&W service bulletin 21446R3, was not carried out during an earlier hot section inspection and immediately preceding the earlier oil loss event.
HISTORY OF FLIGHT On March 6, 2001, approximately 0740 Pacific standard time, a de Havilland DHC-8-102, N822PH, registered to First Security Bank NA, and crewed by an airline transport pilot, a commercial pilot, and a flight attendant, sustained substantial damage during an in-flight fire within the number two engine nacelle while on final approach to Portland International Airport, Portland, Oregon. The three crew and 30 passengers were uninjured. Visual meteorological conditions existed and an IFR flight plan was in effect. Flight 2325 was being operated by Horizon Air as a regularly scheduled 14CFR121 passenger flight, and had departed Seattle, Washington, approximately 0650, destined for Portland. The flight crew reported that on climb out, and the subsequent cruise flight from Seattle, a torque split was noticed between the two engines, which required an approximate, one-half inch split in the power levers to equalize. No other disparities were noted until the aircraft was on a visual approach into Portland during which the inter-stage turbine temperature (ITT) for the #2 engine began increasing and a vibration developed. The ITT continued to increase, and when the landing gear was lowered the crew noted the smell of smoke. The crew advised the Portland air traffic control tower (ATCT) of the event requesting emergency equipment, and the number two engine's condition lever was placed in the "feather" position. The aircraft landed on runway 10R and during the landing the Portland ATCT advised the crew of smoke coming from the right side of the aircraft. Simultaneously, the number two engine fire warning "T" handle illuminated. The aircraft was brought to a stop on the runway, the "engine fire - shutdown on ground" checklist was executed and the passengers were ordered to evacuate using the main cabin door and airstairs. According to the crew, both fire bottles were discharged into the number two engine compartment and the fire was extinguished. DAMAGE TO AIRCRAFT Post-accident visual examination of the number two engine revealed that the number five (compressor) bearing was destroyed as well as its associated air seal. There was evidence of oil leakage and fire within the breather case and compressor section, and the breather tube had melted free allowing hot air to escape into the engine compartment. Further examination of the number two engine nacelle area revealed that the strength of structural members within the nacelle had been weakened to the extent that the entire nacelle forward of the wing spar required replacement. AIRCRAFT AND ENGINE INFORMATION N822PH, a de Havilland DHC-8-102, was a 40 passenger aircraft equipped with two Pratt & Whitney PW120A turboprop engines. The number two engine, serial number PC-E120412, had 27,391.6 hours of total time and had been last inspected (hot section) 180.2 hours previously on January 22, 2001. According to a Federal Aviation Administration (FAA) inspector, engine PC-E120412 was removed from N814PH (another of the company's DHC-8 aircraft) for a scheduled hot section inspection on May 29, 1999. The engine shop performed the inspection in accordance with the specified work scope, but during the inspection, maintenance progressed beyond the hot section inspection work scope exposing an area of the engine affected by Pratt & Whitney Service Bulletin (SB) 21446R3 (refer to ATTACHMENT SB-I). This service bulletin calls for the replacement of the accessory drive spur gearshaft and associated hardware. The service bulletin was coded "R" in the Horizon Air PMP-PW100 (maintenance procedures) document (bulletins coded "R" must be accomplished whenever the area is exposed during a shop visit). According to the FAA, this service bulletin was not accomplished during the previously described maintenance. The engine was not installed on an aircraft until January 27, 2001, when it was installed in the number one position of DHC-8, N828PH. The following day (28 January) the aircraft was flown 0.3 hour on an intended repositioning flight from Portland, Oregon, to Boise, Idaho. During this flight, the number one engine oil pressure warning light illuminated and, according to an entry in the aircraft log, the crew documented "#1 engine oil pressure light came on. Accomplished engine shutdown checklist." The aircraft returned to Portland, and a post flight examination by maintenance personnel revealed the engine to be 15 pints low on oil. The FAA inspector also determined that the flight crew had, in fact, not shut down the engine as indicated in the aircraft log, but rather the engine was maintained in an operational state at the Captain's discretion by placing the power lever in the flight idle position and the condition lever at the Start & Feather position, both in accordance with the DHC-8 flight standards manual under the title "Oil Pressure between 40-55PSI." According to the de Havilland DHC-8 flight manual, normal engine oil pressure is 55 to 65 psid (pounds per square inch differential), oil pressure between 40 to 55 psid is allowable at engine speeds less than 75% NH (high pressure rpm), and oil pressure below 40 psid, with the exception of engine spool up during start, requires that the engine be shut down (refer to ATTACHMENT FM-I). This information is mirrored in the DHC-8 flight manual emergency procedures section (refer to ATTACHMENT EP-I). According to the Pratt & Whitney de Havilland DHC-8 Maintenance Manual (05-50-00), "Unscheduled Maintenance Inspections," section 5Q. "Low oil pressure or loss of oil pressure," the maintenance procedures to be executed in the event of low/loss of oil pressure state: "(1) Check engine/aircraft oil pressure indicating system. If satisfactory and the engine was shut down as required by the flight manual, carry out the following:" procedures "a" through "m" (refer to ATTACHMENT MM-I). According to the FAA examination of actions taken by Horizon Air maintenance following the removal and inspection of engine PC-E120412, the maintenance procedures ("a" through "m" noted above) were not fully executed, i.e., items "K" and "L" (monitor oil consumption for 65 flight hours and check the engine and reduction gearbox chip detectors daily until 65 flight hours is exceeded) were not accomplished (refer to ATTACHMENT MM-I). Although the aircraft's logbook contained the entry indicating that the #2 engine had been shut down, ground crew personnel observed the aircraft taxiing in to the maintenance facility with both engines operating. The observation that the #2 engine was still running when the aircraft returned, was not passed on to the engine maintenance crew who had only the logbook entry to rely upon. The engine was reserviced with oil and a ground run conducted, during which oil was observed blowing out of the engine breather tube. Further investigation revealed that the stop plug assembly in the accessory drive spur gearshaft was missing. According to a representative from Pratt & Whitney, the maintenance which progressed beyond the hot section inspection work scope of May 29, 1999, and into the area of the engine affected by Pratt & Whitney Service Bulletin (SB) 21446R3, would have required the removal and reinstallation of the previously described missing stop plug. The representative also indicated that if the plug backs out, the normal consequence is to vent engine oil overboard through the breather tube. The engine was removed from N828PH for corrective maintenance including the compliance with service bulletin 21446R3, and the engine was subsequently installed on N822PH on February 7, 2001. The engine was then operated for 179.9 hours between February 7th and the accident. Following the accident, the engine was removed from N822PH, and shipped to the facilities of Pratt & Whitney Canada, St. Hubert, Quebec, where disassembly and examination of the engine was conducted. TESTS AND RESEARCH The engine disassembly and examination revealed three areas of significance (refer to attached Pratt & Whitney report PWT-2616 for additional details and graphics): 1. The Number Five roller bearing cage was fractured and the bearings were loose. The roller pockets within the bearing cage showed evidence of severe roller skewing and all the bearing cage fracture surfaces were heavily smeared. All of the rollers were severely worn/flattened and several rollers displayed severe end wear. The Number Five bearing inner race showed evidence of rubbing on the raceway and shoulder. The Number Five bearing outer race was found properly installed and secure and the raceway showed severe rubbing. The bearing cavity and cover plates showed no evidence of fire damage or overheating. The Number Five bearing seals exhibited severe rubbing. The Number Five bearing oil nozzles showed secondary impacts at the orifice. The oil nozzles were flow checked and found unblocked. 2. The P2.5/P3 switching valve to rear inlet case sealing air tube (P/N: 3033920) was found disconnected approximately three inches from the ferrule at the switching valve housing. The tube brazing at the ferrule, as well as several brackets, displayed melted, and re-solidified braze material splattered on the tube surface at the bracket attach points and the ferrule end of the tube. Additionally, the tube was heat discolored, and bent at one location. 3. The sealing tube (NL probe port, P/N: 3106022-01) on the right (outboard) side of the engine was found melted away and the adjacent Number Five bearing vent tube showed signs of fire distress. The sealing tube attach bolts were still bolted to the port with the remaining section of the sealing tube bolting flange. ADDITIONAL INFORMATION Pratt & Whitney Canada issued revision three (R3) to service bulletin (SB) 20914 on October 15, 1991 (refer to ATTACHMENT SB-II). This service bulletin applied to a number of Pratt & Whitney engines, among them 'All PW120A engines prior to serial number PC-E121019 and not incorporating SB 20982.' Service bulletin 20914 applied to engine PC-E120412 on N822PH. The purpose of service bulletin 20914R3 was "to improve the durability of the sealing tube located in the optional NL sensor port under high temperature conditions and to facilitate removal of [the] new sealing tube" and "to improve the durability of the external air tube connecting the P2.5/P3 switching valve to rear inlet case, under high temperature conditions." The service bulletin was not mandatory, however, FAA airworthiness directive 94-11-11 (refer to ATTACHMENT AD-I), effective July 25, 1994, was issued addressing the P2.5/P3 switching valve to the rear inlet case sealing tube and the NL sensor port essentially making service bulletin 20914R3 mandatory. This AD was applicable to Pratt & Whitney engines PW118A, PW123, PW124B, PW125B, and PW126A, but did not include the PW120A series engine. On January 28, 2002, Transport Canada issued airworthiness directive CF-2002-10 addressing Pratt & Whitney PW118, PW120, PW120A and PW121 engines not incorporating service bulletin 20914. The AD was effective March 1, 2002, and made service bulletin 20914 revision R4, a slightly updated version to revision R3, mandatory (refer to ATTACHMENT CAD-I).
The failure of the number 5 engine bearing assembly followed by the disconnection of the P2.5/P3 switching valve to rear inlet case sealing air tube and the melting of the NL probe port (sealing tube) which allowed an oil fed fire beyond the constraints of the engine casing and into the engine nacelle. A contributing factor was the company's failure to follow several maintenance procedures within the maintenance manual after a previous oil loss event. A second factor was the omission of the PW120A engine from the airworthiness directive issued by the FAA which mandated the completion of Pratt & Whitney service bulletin 20914. The lack of inclusion of the PW120A engine in the AD resulted in the company’s correct interpretation that the service bulletin was not mandatory.
Source: NTSB Aviation Accident Database
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