Boeing is preparing to perform what is thought to be the first de-rate engine tests on the 787 since the model began flying in December 2009.
Until now all 787s have been powered by 67,000-lb rated Rolls-Royce Trent 1000G or General Electric GEnx-1B67s. Now Boeing is poised to start tests of an improved Trent 1000 standard, complete with all the software and hardware upgrades incorporated after last year’s intermediate pressure and surge problems, and to fly it de-rated to 64,000 lb thrust.
First, a quick reminder of thrust rating means. Airlines set limits to the thrust level an engine is to produce under normal operating conditions. This limit is called the "thrust rating" of the engine. Setting a thrust rating below the maximum available level of thrust decreases fuel consumption, and increases engine life. The rating is determined by expected operating conditions, so that heavier loads or at higher altitudes require a higher thrust rating than takeoffs at lighter loads or near sea level. The flight management/thrust management computers of aircraft use the thrust rating to develop proper engine control signals.
What is not known currently is if the updated engine standard also incorporates the longer-term Package B mechanical improvements planned for the initial fuel burn reduction goals of early service entry aircraft. Significantly, the first 787 to fly with the newest change will be ZA002, the aircraft grounded for the past six weeks since its return to the Northwest from Texas where it suffered the infamous in-flight electrical fire. The long-planned return to flight has been “off/on” all week say sources, but now looks as if it might happen this weekend – possibly on Sunday Jan 16.
Trent 1000 tests set to expand on ZA002 (Guy Norris)
The plan, as it stands, is to conduct an initial flight to check-out the overall aircraft functionality as well as the engine electronic control. Pending a successful test, ZA002 will then land and the “thrust plug” – which tells the engine what thrust limits to operate at – will be changed from 67,000 lb to 64, 000 lb. The busy day will officially mark ZA002’s re-entry to the rapidly rebounding flight test program.
ZA001, recently active testing various autoland conditions, is poised for stability and control work over the weekend. However, Boeing Flight Test planners are on alert for any airport within a few hours flying distance of Seattle where the wind is blowing directly down the runway. If such a combination is detected, ZA001 will temporarily abandon stability testing and instead check out the autoland system with a head-on wind condition.
Later this weekend, assuming no further changes, ZA001 is set to undertake a series of ground tests that may well have a bearing on whether or not the FAA will perform the final sign-off on Boeing’s revised certification and program schedule. The aircraft is due to be hooked up to the FETS (flight emulation testing system) to go through a series of realistic failure scenarios. The FETS, which was used to simulate flight conditions during the 787’s pre-flight system gauntlet checks, will likely run through aspects of the revised power distribution system software developed in the wake of the Laredo fire incident.
Two other active 787 test aircraft, ZA004 and ZA005, meanwhile continue ground-based certification tests and nautical air miles, fuel burn tests respectively.