New-technology engines are coming off the wing of aircraft much sooner than anticipated, AerCap CEO Aengus Kelly remarked on August 11 in the lessor’s earnings call. This remark came as a surprise to some, as it was believed that the technical issues that these engines suffered from in recent years were all over. Or is there something happening below the radar? Are new engine types still having tech issues? Engine makers aren’t readily offering insight into what is happening in the workshops, so we looked for another way to get a picture of the situation. One is looking at Airworthiness Directives (AD) that are issued by the regulators, the FAA in the US, and EASA in Europe among the most influential players. If they issue an AD, then a problem must be serious enough to require inspections and/or part replacements. Which sometimes can result in taking an engine off its wing, as AerCap is seeing. For this story, we checked and analyzed ADs that have been issued since January 1. Some are final or updated versions of previous directives, others are new ones after recent problems were found. We specifically searched for ADs for the new generation of turbofans, so the Pratt & Whitney Geared Turbofan, the CFM LEAP, the General Electric GEnx, and the Rolls-Royce Trent 1000 and XWB. Pratt & Whitney Geared Turbofan: January 12 – FAA AD for the PW1500G on the Airbus A220 and PW1900G on the Embraer E190-E2 and E195-E2, requiring the removal and replacement of the High-Pressure Turbine (HPT) 1st and 2nd stage disks. A subsurface material defect was found to be the root cause for an inflight shutdown on an International Aero Engines V2500 Airbus A321ceo. Although totally different from the GTF, P&W and IAE traced engines with parts that have similar material. Which is the Geared Turbofan, but only the two versions included in the AD. “This condition, if not addressed, could result in uncontained HPT disk failure, the release of high-energy debris, damage to the engine, damage to the airplane, and loss of the airplane”, says the AD, which estimated that only eight engines in the US fleet were affected. The Pratt & Whitney Geared Turbofan. (P&W) July 15 – The PW1500G and PW1900G were part of a final rule of another FAA AD issued in July, superseding a 2021 AD. This one was issued after inflight shutdowns on two Airbus A220s that were traced to a software problem and the compressor intermediate case (CIC). The original AD required “repetitive borescope inspections of certain low-pressure compressor (LPC) rotor 1 until replacement of electronic engine control (EEC) full authority digital electronic control (FADEC) software with updated software.” Since then, P&W redesigned the compressor intermediate case and updated the FADEC software. Still, the FAA required repetitive borescope inspections and replacement of the LPC rotor 1 to continue. CFM LEAP: January 19: EASA AD for the LEAP-1A used on the Airbus A320neo family, following revised time limits and maintenance checks in the Airworthiness Limitation Section. Affected items are Stages 6-10 Compressor Rotor Spools, High-Pressure Turbine (HPT) Rotor Interstage Seals, Stage 2 HPT Rotor Disks, Stage 1 Low-Pressure Turbine (LPT) Disks, Stage 2 LPT Disks, Stage 3 LPT Disks, and Stage 4 LPT Disks, having a Part Number (P/N) and serial number (s/n) listed in the Service Bulletins. In addition to revised time limits for new parts, the AD was issued “following investigations related to material anomalies in certain critical parts, it has been determined that the affected parts, as defined in this AD, may have subsurface anomalies developed during the manufacturing process, resulting in a lower life capability. This condition, if not detected and corrected, could lead to failure of the affected parts, possibly resulting in high energy debris release, with consequent damage to, and reduced control of the aeroplane.” April 26 – EASA AD for the LEAP-1B used on the Boeing MAX. Like the one for the -1A in January, the main reason was revised time limits for specific parts numbers They included Stages 6-10 Compressor Rotor Spools, High-Pressure Turbine (HPT) Rotor Mid Seals, Stage 2 HPT Rotor Disks, Stage 2 Low-Pressure Turbine (LPT) Disks, and Stage 3 LPT Disks. April 27 – An EASA AD for the LEAP-1B issued a day later affected the drive shafts of the Transfer Gearbox Module system. After an inflight shutdown after an oil filter bypass indication in 2019, the investigation identified the failure of the Radial Drive Shaft bearing cage as the root cause. Although an AD was issued in 2019 to address the problem, other occurrences have continued since then. “Consequently, CFM published the SB, providing instructions for additional Transfer Gearbox (TGB) inspections for a limited batch of engines not having the modification SB embodied.” The latest AD became effective on May 11 and instructed operators with specific part numbers to inspect the parts within fifty hours after the issuance. The CFM LEAP-1B for the Boeing MAX (CFM International) June 17 – Already under scrutiny with the January 19 AD, the FAA and EASA released another one on the LEAP-1A, specifically addressing the Stages 6-10 of the Compressor Rotor Spools and HPT stage 1 disks with specific part numbers. “Three HPT Rotor Disks from a different engine type have been found to contain iron inclusions. This has been attributed to specific deficiencies in the manufacturing process. Iron inclusion may lead to reduced mechanical properties and failure of an affected part prior to achieving its approved life as published in the Airworthiness Limitations Section of the Engine Manual.” The AD continued: “It has been determined that the affected parts identified in the SB were manufactured using the same processes, and may also have reduced mechanical properties due to iron inclusion. This condition, if not corrected, could lead to failure of affected parts, possibly resulting in high energy debris release, with consequent damage to, and reduced control of, the aeroplane.” The AD became effective on July 1. July 7 – EASA followed up with another AD for the LEAP-1A with specific serial numbers to inspect and repair the High-Pressure Turbine Nozzle Assembly and Stator Stationary Seal. “Occurrences have been reported of non-synchronous vibrations on certain engines. Investigations have shown that this vibration may result in increased interstage seal clearances, resulting in hot gas ingestion and thermal degradation of the high-pressure turbine (HPT) rotor interstage seal and HPT rotor stage 2 disk. This condition, if not detected and corrected, could affect the low cycle fatigue life of the HPT rotor interstage seal and HPT rotor stage 2 disk.” July 19 – The LEAP-1A remained the focus of attention with a revised AD from January, this time covering High-Pressure turbine (HPT) rotor stage 1 blades with specific part numbers. The AD was motivated after “occurrences have been reported of finding cracked affected parts on engines operated extensively in the MENA (Middle East North Africa) regions. (…) To address this potential unsafe condition, CFM issued the SB, as defined in this AD, providing instructions to accomplish borescope inspections (BSI) of HPT stage 1 rotor blades and stator nozzles, in addition to those already included in the recommended maintenance schedule.” July 20 – The most recent AD on the LEAP was issued by the FAA on July 20 and covers only the -1A again. But the reason dates back to January 2020, when an Airbus A319neo (test aircraft) suffered high vibrations. “A subsequent engine disassembly by the manufacturer revealed three areas of missing material on the HPT rotor interstage seal and multiple radial and circumferential cracks on the forward arm. The manufacturer's investigation determined that the degraded HPT rotor interstage seal failure locations were initiated by creep rupture, related to hot gas ingestion due to reduced effectiveness of the stage 2 HPT nozzle honeycomb seals, a condition that could impact the HPT rotor stage 2 disk low-cycle fatigue life.” CFM released a Service Bulletin in June 2020, but two years later, the FAA responded with a new AD that requires inspection of the stage 2 HPT nozzle assembly honeycomb and HPT stator stationary seal honeycomb. “Depending on the results of the inspection, this AD requires replacement 3 of the stage 2 HPT nozzle assembly honeycomb, HPT stator stationary seal, HPT rotor interstage seal, and HPT rotor stage 2 disk.” Etihad Boeing 787-9 powered by the General Electric GEnx-1B. (Etihad) General Electric GEnx: February 14 – FAA AD for the GEnx-1B (Boeing 787) and -2B (747-8). It was prompted after GE reported “two findings of sheared compressor discharge pressure (CDP) bolts during engine shop visits. This AD requires initial and repetitive inspections of the CDP bolted joint and, depending on the findings, a piece part inspection of the stages 6-10 compressor rotor spool, CDP seal, and high-pressure turbine (HPT) rotor stage 1 disk.” The AD followed a Notice of Proposed Rulemaking in October 2021 and affected 320 engines in the US. February 22 – Another FAA AD was issued for the GEnx only a week later, after a report of an inflight shutdown on a 747-8F following overspeed and fire warnings in July 2021. The subsequent investigation by GE revealed “an improperly torqued fuel metering unit (FMU) bypass valve (BPV) plug. This AD requires a shim check inspection of the FMU BPV plug and, depending on the results of the inspection, replacement of the FMU. (…) This condition, if not addressed, could result in loss of engine thrust control, IFSD, and reduced control of the aircraft. The FAA is issuing this AD to address the unsafe condition on these products.” During the investigation, a fuel system leak related to a lose FMW BPV was found to have happened on a 787-10 one month later. Rolls-Royce Trent: June 30 – The FAA and EASA issued a revised AD of the original one from September 2019 to address an issue on the XWB, used on the Airbus A350-900 and -1000. Although not related directly to the engine itself, it covered the front engine mount support structure. “The front engine mount support structure (EMSS) consists of the low-pressure compressor (LPC) outlet guide vane (OGV) assembly and OGV outer mount ring assembly. Revised analysis of these parts, when the front engine mount (FEM) is engaged in the fail-safe condition, has now been undertaken using more advanced modeling techniques. This analysis predicts that, once the FEM is in the fail-safe condition, the most highly stressed LPC OGV has a life that could be substantially less than one shop visit interval. This condition, if not detected and corrected, could lead to failure of the EMSS, possibly resulting in engine separation and reduced control of the aeroplane.” Initially, it was thought that only the XWB-84 (and -75, -79, and 79B) were affected, but the problem was also traced to the more powerful XWB-97 on the A350-1000. The AD required the inspection and replacement of the OGV outer mount ring assembly. July 14 – EASA issued an AD for the Trent 1000, used on the Boeing 787, after updating the time limits for maintenance. It covered the so-called Package C, which includes an updated Intermediate Pressure compressor, IP turbine, and High-Pressure Turbine. An AD was issued in 2020, but since then, Rolls-Royce introduced more restrictive tasks and limitations, including updating declared lives of certain critical parts. Operators were required to “replace each component before exceeding the applicable life limit.” The bottom line What can we conclude from all these ADs? First, not all are new but follow previous directives, although this seems to indicate that the original issue is still there. Second, there are ADs for the GTF and LEAP that could require extensive off-wing time for the repair and/or replacement of parts. It affects the Airbus A220, Embraer E2-series, but most of all the Airbus A320neo family. With four ADs for the LEAP-1A since June, MRO shops have plenty of work to do to inspect these engines and likely remove them. That seems to be the point that Aengus Kelly wanted to raise in the AerCap presentation. He didn’t mention any names, but with more and more LEAP-1As literally under scrutiny and out of service, that puts the pressure on the supply chain to provide sufficient spare engines. This eats into the availability of engines for new aircraft that are still on the assembly lines, hence the problem of ‘gliders’ of engine-less aircraft sitting around factories of Airbus, Boeing, and Embraer.
