GE Aviation

Following a thorough review of NPRM FAA-2009-0328, proposing an AD for GE CF34-1A, CF34-3A, CF34-3A1, CF34-3A2, CF34-3B, and CF34-3B1 engines, GE proposes the following items for consideration: General Discussion In the “Discussion” section of the NPRM the FAA states that due to thermal damage it was not possible to determine the cause of the under cowl fire. This is not consistent with the GE fire investigation. GE Aviation Commercial Flight Safety has investigated and produced a report on the under cowl fire associated with this stage 1 fan blade separation event. The report concludes that the most probable cause of the under cowl fire was the separation of the Variable Geometry (VG) Head Line from its end fitting attachment at the Main Fuel Control (MFC) during the stage 1 fan blade separation. In this event, the Head Line separation was attributed to the positioning of the line’s end fitting at the MFC. The correct position of the VG Head Line end fitting at the MFC should be down, towards the 6 o’clock position. At this position there is adequate slack in the line routing to accommodate any movement of the Accessory Gearbox (AGB). On the event engine, the VG Head Line fitting at the MFC was positioned outboard facing towards the 9 o’clock position instead of the 6 o’clock position. With the VG Head Line end fitting at this position, the slack in the VG Head Line was reduced. It was this reduced slack condition in conjunction with the AGB mount pins fusing that resulted in the VG Head Line separating from its end fitting at the MFC. This line separation allowed atomized fuel to spray onto the hot Combustion Case and ignite. A properly positioned VG Head Line fitting at the MFC did not separate during the Fan Blade Out certification test even with the AGB mount pins fused. The “Discussion” section also contains a statement regarding the accessory gearbox (AGB) that should be clarified. The statement reads, “The investigation also revealed that the accessory gearbox had separated from the engine, possibly contributing to the actuator hose failure.” The AGB is specifically designed to have the mounts uncouple during a high load event, such as a fan blade out, and is secured to the engine by secondary restraint cables. The actual condition of the AGB was that the left hand (ALF) fusible mount was sheared and had decoupled under this high load condition per design intent, leaving the AGB supported on this side by the secondary restraint cable. Therefore, the AGB had not separated from the engine and the fact that the AGB partially decoupled was as intended, and should not have contributed to the hose failure had the hose been properly aligned. Unsafe Condition The Unsafe Condition statement in paragraph (d) reads: “This AD results from a report of an under-cowl fire, and a failed fan blade. We are issuing this AD to prevent failure of certain part number (P/N) and serial number (SN) fan blades and aft actuator head hoses, which could result in an under-cowl fire and subsequent damage to the airplane.” It is GE Aviation’s position that by the definition of a “controlled fire” there is no subsequent damage to the aircraft, because the fire was contained within the fire zone and was controlled and extinguished. The event engine was subject to a controlled fire and did not hazard the aircraft. Compliance Instructions 1. Paragraph (f)(6) for Repetitive Visual Inspection of the Fan Blade Abradable Rub Strip for Wear references SB CF34-AL S/B 72-0250 R1 and instructs that within 75 cycles-since-last inspection (CSLI) or 100 hours-since-last-inspection (HSLI), whichever occurs later, a visual inspection of the fan blade abradable rub strip for wear is to be conducted in accordance with paragraphs 3.A.(1)-3.A.(2) of the Accomplishment Instructions of GEAE SB CF34–AL S/B 72–0250, Revision 01. As noted in the front matter of the NPRM and summarized here in Table 2, this instruction differs from the GE SB in that the alternate method of compliance by using GE Remote Diagnostics for monitoring the fan blade health included in the SB is excluded from the NPRM. The blade tang cracking algorithms developed by GE in support of the existing field program have been validated analytically as well as in the field and contributed substantially to finding three cracked blades in operation in 2008. Disallowing the use of GE Remote Diagnostics as an alternate means of compliance will create a significant burden for Regional Jet operators with affected fan blade SN installed, as the 75 cycle or 100 hour recurrent interval does not align with any regular scheduled engine maintenance. It also creates an inequality for monitoring the fan blade health of fan blades listed by SN in CF34- AL S/B 72-0245 R1 and CF34-BJ S/B 72-0229 R1 because the proposed AD would allow recurrent eddy current inspection (ECI) for Business Jet operators in accordance with CF34-BJ S/B 72-0229 R1 paragraphs 3.A or 3.B (reference paragraph (g)(6) in the NPRM). GE recommends that the GE Remote Diagnostics be included in paragraph (f)(6) as an alternate means of compliance for monitoring fan blade health or, at a minimum, that a recurrent ECI at 600 cycle intervals be permitted for consistency between the Regional Jet and Business Jet operators. 2. Paragraph (g)(3) for “Initial Eddy Current Inspection of the Fan Blades” references SB CF34-BJ S/B 72-0229 R1 and instructs that for fan blades, P/N 6018T30P14, with more than 850 CSN, but fewer than 1,200 CSN on the effective date of the AD, within 350 CIS after the effective date of the AD, perform an initial ECI of the fan blades for cracks in accordance with paragraphs 3.A. or 3.B. of the Accomplishment Instructions of GEAE SB CF34–BJ S/B 72–0229, Revision 01. This specifically excludes fan blades with 1,200 CSN or greater on the effective date of the AD. Current GE estimates indicate that there will be ~450 affected fan blades in operation in Business Jet applications which will have 1,200 CSN or greater on the effective date of the AD. Therefore, GE recommends that paragraph (g)(3) be modified to read: “For fan blades, P/N 6018T30P14, with more than 850 CSN, but fewer than 1,200 CSN on the effective date of the AD, within 350 CIS after the effective date of this AD, perform an initial eddy current inspection (ECI) of the fan blades for cracks.” This wording is consistent with the compliance recommendation in the GE SB. This recommendation is summarized in Table 3. 3. SB CF34-AL S/B 72-0250 R1 and CF34-AL S/B 72-0245 R1 apply both to regional jet operators and also to a small number of business jet operators who fly under the RJ manual. These business jet applications may include both CF34- 3B1 and CF34-3A1 models. The proposed AD distinguishes between regional jet and business jet applications based on engine model and, in the case of the CF34- 3A1 model, the life limit of the fan drive shaft, P/N 6036T78P02. For consistency between GE service bulletin instructions and the proposed AD, GE recommends that another, different, method of separating the CF34-3A1 model into the appropriate population be used for enhanced clarity. GE recommends the following suggestions for consideration. A. GE recommends the use of aircraft model and version number. The business jet operators who fly under the RJ manual are operating CL-600-2B19 aircraft (versus business jet operators who fly under the BJ manual and are operating CL- 600-2B16 aircraft). The engines on the CL-600-2B19 can be either CF34-3A1 or CF34-3B1 engines and include the Corporate Jet Liners (converted regional jet aircraft), Challenger 850SE, and Challenger 850 aircraft. The aircraft with the early CF34-1A engines were certified as CL-600-2A12 and then they moved to CL-600- 2B16 (these are the CL601-3R, CL604 and CL605). The pertinent paragraphs would then read as follows: (f) “For CF34–3A1 engines with fan drive shaft, P/N 6036T78P02, and airworthiness limitation section life limit of 22,000 CSN, or CF34–3A1 engines with fan drive shaft, P/N 6036T78P02, and airworthiness limitation section life limit of 15,000 CSN that are operating on CL-600-2B19 certified aircraft, and CF34–3B1 engines with fan blades, P/Ns 6018T30P14 or 4923T56G08, that have a fan blade SN listed in Appendix A of GE Aircraft Engines (GEAE) Service Bulletin (SB) CF34–AL S/B 72–0245, Revision 01, dated July 3, 2008, do the following:” (g) “For CF34–3A1 engines with fan drive shaft, P/N 6036T78P02, and airworthiness limitation section life limit of 15,000 CSN, that are operating on CL- 600-2A12 or CL-600-2B16 certified aircraft, and CF34–1A, CF34–3A, CF34–3A2, and CF34–3B engines with fan blades, P/N 6018T30P14 or P/N 4923T56G08, that have a fan blade SN listed in Appendix A of GEAE SB CF34–BJ S/B 72–0229, Revision 01, dated July 30, 2008, do the following:” B. If use of the certified aircraft model is not feasible, GE then recommends the use of the model designation and service bulletin number engraved on the engine name plate. The life limits for CF34 engine models are established on the basis of the model designation and, for 3A1/3B1 engines operating under the Regional Jet manual, the service bulletin number engraved on the engine name plate. Service bulletin CF34-AL S/B 72-0146 and CF34-AL S/B 72-0147 cover the use of CF34- 3A1/3B1 engines in regional jet and business jet applications, respectively. These bulletins define the appropriate life limit chapters to be used. Incorporating this change, the pertinent paragraphs would then read as follows: (f) “For CF34–3A1 engines with fan drive shaft, P/N 6036T78P02, and airworthiness limitation section life limit of 22,000 CSN, or CF34–3A1 engines with fan drive shaft, P/N 6036T78P02, and airworthiness limitation section life limit of 15,000 CSN that are in compliance with GE SB CF34-AL S/B 72-0147, and CF34– 3B1 engines with fan blades, P/Ns 6018T30P14 or 4923T56G08, that have a fan blade SN listed in Appendix A of GE Aircraft Engines (GEAE) Service Bulletin (SB) CF34–AL S/B 72–0245, Revision 01, dated July 3, 2008, do the following:” (g) “For CF34–3A1 engines with fan drive shaft, P/N 6036T78P02, and airworthiness limitation section life limit of 15,000 CSN, that are not in compliance with GE SB CF34-AL S/B 72-0147, and CF34–1A, CF34–3A, CF34–3A2, and CF34–3B engines with fan blades, P/N 6018T30P14 or P/N 4923T56G08, that have a fan blade SN listed in Appendix A of GEAE SB CF34–BJ S/B 72–0229, Revision 01, dated July 30, 2008, do the following:” C. If the above recommendations are not acceptable, at a minimum, the addition of CF34-AL S/B 72-0245 R1 as a reference in paragraph (g) is recommended to allow business jet operators who fly under the regional jet manual to determine whether they have any of the affected blades installed. These operators may not have ready access to SB CF34–BJ S/B 72–0229 R1 and would have difficultly determining whether they are affected by the proposed AD. Paragraph (g) would then read: “For CF34–3A1 engines with fan drive shaft, P/N 6036T78P02, and airworthiness limitation section life limit of 15,000 CSN, and CF34–1A, CF34–3A, CF34–3A2, and CF34–3B engines with fan blades, P/N 6018T30P14 or P/N 4923T56G08, that have a fan blade SN listed in Appendix A of GEAE SB CF34–BJ S/B 72–0229, Revision 01, dated July 30, 2008, or alternately, listed in Appendix A of GEAE SB CF34–AL S/B 72–0245, Revision 01, dated July 30, 2008, do the following:” 4. Paragraph (f) lists the issue date of GE SB CF34-AL S/B 72-0245 R1 as July 3, 2008, the actual issue date for that SB is July 30, 2008. This date is listed correctly elsewhere in the proposed AD. Modifying the proposed AD to reflect these changes would more clearly identify affected populations and compliance requirements and still meet the FAA’s purpose in issuing the Airworthiness Directive.