Safety action taken
As a result of this occurrence and other similar incidents, the engine manufacturer Pratt & Whitney have advised the ATSB that they are taking the following proactive safety actions:
P&W has processed an engineering change that revises OTD material with higher temperature capability. The redesigned hardware will be available from November 2019 and will be recommended for incorporation when the LPT [Low Pressure Turbine] module is disassembled at a minimum.
All engines are planned to incorporate redesigned OTDs at the next shop visit when a major engine flange is separated for the purposes of performing maintenance regardless of planned LPT maintenance. This interval is approximately 3000 cycles on average, but can vary depending on the specifics of each carriers’ operating characteristics. This recommendation will be made with P&W Service Bulletin numbered PW4G-100-A72-261, which is pending release at this time.
New production PW4000 100” Advantage70 engines are no longer being produced. At overhaul, engines that are re-built prior to November 2019 will not receive the redesigned OTD. However, every engine shop visit prior to November 2019 where the LPT is disassembled will be recommended for installation of a full set of non-engine run, current design OTDs. This practice will provide a benefit to the fleet by removing OTDs that were potentially exposed to elevated temperatures.
The ATSB welcomes the proactive safety action taken by Pratt & Whitney to develop an improved outer transition duct. However, the ATSB believes that Service Bulletin PW4G‑100‑A72‑261 should hold a mandatory compliance status due to the significant number of OTD failures in a relatively short space of time. This will also ensure a fleet-wide compliance with the service bulletin. Additionally, as the installation of the redesigned components is at the operators’ cost, this has the potential to hamper incorporation of the improved components.
As a result, the ATSB issues the following safety recommendation.