New airliners don’t come along terribly frequently so the first movements of a new jet are bound to attract some attention. Rob Edgcumbe was at Everett when the first Boeing 777X started taxi trials.
Boeing’s plan to follow on from the successful 777-300ER jet is an evolution of that aircraft. The 777X family initially consists of the 777-8 and the 777-9. The fuselage of the 777 family was brought forward in a modified form and mated with a new composite wing design and new GE9X engines. These more efficient engines, combined with the new wing design, allow an increase in fuselage sizes. The 777-8 is similar in size to the 777-300ER while the 777-9 is longer and provides greater capacity albeit with a slightly reduced range. The effect is a step up in capacity from the 777-200LR/777-300ER
The new wing design includes an increase in wing span. However, in order to fit in with existing airport infrastructure, Boeing has adopted a folding wingtip mechanism. This provides the efficiency gains of the wider wing without limiting the aircraft’s utility. It is the first implementation of such technology on a commercial jetliner even though it was originally contemplated for the 777 when it was first designed. At that time no customer wanted the option and, once the join concept was discarded, Boeing was able to make use of the extra wing box space for increased fuel tankage.
The first airframes out of the Boeing factory alongside Paine Field in Everett Washington are 777-9s. The first aircraft was rolled out in a low-key event given that it closely followed the Ethiopian Airlines 737 Max 8 crash. A second airframe followed and both are now on the flightline undergoing preparation for test flying. A third airframe for fatigue testing has also been rolled out of the factory and is now installed in the test fixture on Boeing’s facility. Initial customer jets are not far behind.
A lot of static testing precedes any movement of the aircraft, but the first jet has now commenced taxi trials at low speeds. Normal testing protocol would see taxi speeds progressively increased up to the point of raising the nosewheel to test elevator control authority prior to the official first flight. However, while the testing has commenced, there has been an announcement from GE about an issue with one of the engines on an acceptance test. Details are relatively sparse at the moment but some redesign and testing is required. First flight is undoubtedly affected but for how long is not yet clear. Various press announcements have vague language in them which don’t make it clear whether the delay will be short term or longer. With the fallout from the Max accidents, everyone is probably being very cautious about any decisions made.
Meanwhile, the taxi trials continue. The jet is noticeably quiet. Everett has passenger service with Embraer E175-E1 jets and these seem significantly noisier than the 777-300ERs on production tests. The 777-9 felt even quieter than the 300ER but you don’t know what throttle settings were being used. It is definitely a quiet jet, though. On one test, the wingtips were unfolded as they turned on to the runway and they lowered in to place quickly. An interlock exists to prevent take off power being selected with the wingtips in the folded position.
The tests involve regular braking, so the jet periodically returned to the ramp where a team of flight test staff placed large fans to blow cooling air on the brakes. This was repeated a few times. As the speeds increase, the brake temperatures will increase too but, with further data gathered, presumably the confidence in the brakes at higher temperatures will increase. We shall see how much the speed increases in the coming days. High speed runs may need a full flight clearance in case the jet gets airborne and, with the engine issues, such a clearance may not yet be available.
Below is a video of the jet taxiing to the runway, lowering the wingtips as it lines up and accelerating down the runway for one of the low speed tests.