With the 787 production and flight test program back to normal operations with ZA001 flying again, the spectre of the Trent 1000 engine failure still hangs over the program. While the September 10 engine surge was not related to the August 2 engine failure in Derby, UK, it was a reminder of how the 787's powerplant has moved to the forefront of concerns ahead of the February entry into service with ANA.
Industry officials are becoming increasingly concerned about the potential result of the on-going investigation into the failure. Concerns about the engine's certification, which was granted on August 7, 2007 (07/08/07 on the European calendar), prompted me to ask Boeing if the investigation included an assesment of the basis for certification of the Trent 1000 engine. Here is Boeing's complete response to my question:
The investigation includes a review of safety and continued airworthiness as prescribed by EASA and FAA requirements. The regulatory agencies have methods in place to ensure airworthiness. When the investigation is complete and we have more information about causes and solutions, we will work with the regulatory agencies to comply with the applicable processes. [emphasis mine]There are a few versions as to what transpired on August 2, with indications all pointing to an oil fire in the high pressure compressor drum leading to a failure of the intermediate pressure (IP) shaft. One industry source says once the IP shaft failed, the mounted IP turbine disk moved rearward, causing its blades to impact the low pressure (LP) turbine inlet guide vanes. The result was the separation of the IP turbine disk, which subsequently spun out of the casing and into the test stand.
The same source adds that the "non-adherence to test procedures" was the root cause of the failure, saying that the "stand crew ran more cold starts in close succession than allowed without purging of fuel and oil that accumulate within the engine in places these fluids are not supposed to be."
That result provides more clarity to the "inappropriate operating regime" statement from Rolls-Royce. Though even with a root-cause potentially identified,
While a timeline for the investigation's completion is not known, the result will hopefully bring much sought after clarity.
UPDATE: FAA and EASA certification does not require the engine's casing to contain a failure of the compressor or turbine, as there's no way to contain the disks spinning at a high rate of speed. For example, in May, an urgent recommendation was handed down by the NTSB regarding a spate of uncontained failures on General Electric CF6 engines.
The recommendation clearly spelled out the certification requirements, which dictate that a fan blade-out event must be contained within the casing. The NTSB added: "Engine cases are not designed to contain failed turbine disks. Instead, the risk of an uncontained disk failure is mitigated by designating disks as safety-critical parts, defined as the parts of an engine whose failure is likely to present a direct hazard to the aircraft.