How serious is the failure of a Rolls-Royce Trent 1000 engine on the test bed at Derby, and what will be its impact on the 787 entry-into-service?
More than 24 hours after news broke that a failure had occurred at the U.K engine manufacturer’s facility earlier this month, we seem to be no closer to answering either question. First let’s review a few facts as far as they are known.
Rolls-Royce says the failed engine was built to a ‘Package A’ standard. The engines installed on the first four 787s are configured with ‘Package A’ improvements, devised to tackle part of the 4-5% specific fuel consumption shortfall identified in early development tests. However a further series of improvements developed during the subsequent two-year program delay are being introduced in Package B (below). The delay to the start of 787 flight tests in 2009 meant some of these later improvements were apparently sufficiently mature to be introduced during initial flight tests with units which Rolls described last year as “a hybrid version of the Package A” and “a robust engine to support the flight test program.”
Rolls-Royce’s Trent 1000 built to the improved ‘Package B’ standard is designed to bring performance to within 1% of Boeing’s original specification. Package B includes improved aerodynamics in the six-stage low pressure (LP) turbine, improved cooling flow for the intermediate pressure (IP) turbine and changes to the secondary air system to take off sealing and cooling air at a lower pressure stage. The root-to-tip twist of the fan blade is also slightly altered to match changes in the pressure ratio caused by a concurrent reduction in nozzle area. Rolls has run at least three Package B performance engines and, when last reporting on progress, says all were in line with expectations. In March Rolls was flight testing the first Package B engine on its company 747 flying testbed ahead of delivering finalized engines to Boeing for installation on ZA004.
Initial Trent 1000 engine configuration on ZA003 (Guy Norris)
What Boeing is saying.
“Boeing is actively participating in the investigation into this event with Rolls-Royce. There has been no impact on the flight test program to date as a result of this event.” Of more concern is the fact that Boeing says it is “still evaluating” if the failure might have an impact on the year-end target date for service entry with ANA. Ever since the hold-ups caused by the initial horizontal tail inspection Boeing has already suggested that this may slide into early 2011.
What Rolls-Royce is saying.
The Trent 1000 engine experienced a failure this month on a test stand in Derby with the powerplant in a sea-level testbed configuration at high power. The engine suffered an intermediate pressure turbine-related failure because of what is being characterized as an “inappropriate operating regime.” Rolls-Royce says “we are now investigating in detail and have made good progress in understanding the issue.” The company was also apparently already aware of the issue, and it says later model Trent 1000 builds already have a fix in place, which is now also being installed on engines built to the earlier standard.
The initial report says the failure was uncontained, though this has not yet been confirmed by Rolls. If the design failed to contain the ruptured IPT, Rolls may well be required to rerun some engine certification and type tests. Will this be the case even though the configuration is not completely representative of the Package B configuration which was originally due to be retrofitted to ZA004 within a matter of weeks? Of further concern to Rolls and Boeing must be that the IP system functions in a particularly vital role on the 787 as the power off-take source for the aircraft’s electrical system.
Subsequent comments made by Rolls about having a fix already in place suggest the revised IPT cooling configuration adopted in Package B may address the conditions that contributed to the test failure, as well as forming part of the drive to improve overall efficiency. However, will the failure investigation reveal the need for additional mods to the Package B configuration and, if so, will that inevitably mean delays to the planned retrofit of ZA004 as well as deliveries of production standard engines to Everett?
Investigations are focused on the IPT (Guy Norris)
Flight test status
Boeing’s statements about the failure not having an immediate impact on the test program appear to be accurate so far.
ZA001, now temporarily based at Edwards AFB, Calif, flew an aero performance flight to Victorville. Wednesday 18th is expected to see the aircraft fly to Roswell, New Mexico where the 787 will undertake wet runway tests. Boeing prefers to use Roswell for this work as the ex-USAF base runway is un-grooved, making it a more challenging test condition.
ZA002. Ground tests at BFI expected Wed 18th.
ZA003. In lay-up.
ZA004. Flight loads survey, expected to resume from Victorville, Calif on 18th.
ZA005. Ice shapes handling qualities and stall speed tests.
ZA006. Pre-flight ground system work.