A350-1000 pilot report - AW&ST

Aviation Week Flies Airbus’ Biggest Twin-Engine—A350-1000 Tim Wuerfel  The A350-1000 is still a rare sight at airports. Only two of the aircraft have been delivered to airlines so far, one each to Qatar Airways and Cathay Pacific Airways, and only a few pilots are regularly flying Airbus’ largest twin-engine aircraft.  But the aircraft is ready to make its mark, with its 8,400-nm maximum range and 366-passenger typical seating. Cathay will use its first A350-1000 on a new nonstop service to Washington, at 7,085 nm and approximately 17 hr., the longest flight by any airline out of Hong Kong. Qatar will use the bigger aircraft to offer 44 more seats on the Doha-London Heathrow route than available on its A350-900s. Cockpit enhancements designed to minimize pilot workload Automated emergency descent mode reduces reaction time Aviation Week was invited to test-fly Airbus’ biggest twin from its Toulouse home base. The flight was under the command of Peter Chandler, senior experimental test pilot, who was in control for the first flight of the 1000—which is not only the largest version of the A350 but also an aircraft that brings a new level of automation to the cockpit.

The Airbus A350-1000 is 7 m (23 ft.) longer than the A350-900 and seats about 40 more passengers. Its heavier maximum takeoff weight is utilized by a main landing gear with six-wheel bogies. Credit: Airbus

We flew MSN059, the first A350-1000 prototype. It was parked between two A350-900s, each 7 m (23 ft.) shorter. Airbus’ special -1000 livery shows the three zeros as circles to illustrate the enlarged six-tire main landing gear bogie. The wing has the same span as the -900, but its trailing edge is extended by 0.3 m to improve slow-flying characteristics and carry up to 36 metric tons (79,400 lb.) in extra weight—which takes the optional maximum takeoff weight to 316 metric tons. The A350 is the first long-range Airbus that does not incorporate a trim tank in the tail section to move the center of gravity. Instead, to save fuel in cruise, the aircraft is able to shift its center of lift in flight by deflecting the trailing-edge flaps by up to 2 deg.  The No. 3 cabin doors behind the wing have been moved aft by one frame to give enough clearance from the larger wing for service vehicles. All doors are now surrounded by composite materials, and this increases the use of carbon fiber in the primary structure to 54%. Thrust of the big Rolls-Royce Trent XWB engines has been increased to 97,000 lb. at takeoff from 84,000 lb. for the heavier A350. The manufacturer and customers alike say they are satisfied with the performance of the engine, of which lower-rated versions are flying on about 180 A350-900s. The engines have reached a dispatch reliability close to 99.9% in the last 12 months, the best entry into service of any Trent. Upon entering the cabin of our aircraft, registered F-WMIL, I got a good impression of the size of the XWB fuselage, as it is filled only with test equipment, a station for the flight-test engineers, a few extra seats and water tanks in the back to create different weight and center-of-gravity conditions. In the spacious cockpit, on the right side behind the pilots’ seats, a station allows access to the systems for maintenance technicians and was used by the flight-test engineers on our flight. Because the windows cannot be opened, there is more space outboard of the pilots, making the cockpit even wider and adding storage space below the huge side windows. These allow excellent visibility that reminded me of the extraordinary view from the cockpit of the MD-11. Chandler took the right seat, and I sat in the left to start preparations. Our aircraft was electrically powered by external ground equipment so we could look at the cockpit design and changes from the -900. Of the six identical large-format liquid-crystal displays, the outboard and lower center panels are now touch screens and can mirror their display to another screen for briefings or for the crew to look at a technical aspect on the center screen.

I see this as a major improvement over the electronic flight bags that have been added to existing cockpits, as these require me to turn my back on my colleague while explaining an approach or a problem while at my screen. On the A350, you no longer have to turn around to check the nonverbal reaction of the other pilot. Even when we encountered some turbulence, the touch-screen experience is no different from trying to hit the right switch when the aircraft is shaking. One thing that attracted my attention was that there are no permanent lights on the A350 for the landing gear indication as there have been on all previous Airbus aircraft. Instead, the indication is visible on the system-display (SD) page for the gear and is presented with any landing gear actuation or if a problem is sensed. As on the A380, there are no moving trim wheels next to the thrust levers, but an on-screen indication is situated below the primary flight display (PFD). Next to it is a parking brake set indicator; the “triple pressure indicator” from earlier types has been eliminated. These are small examples of changes pilots must get acclimated to when flying the A350. But it is only logical to make these indications non-permanent, as you need them only for short phases, and they come up automatically if a problem is sensed. Chandler led me through the inputs to the onboard information system (OIS). This was mostly self-explanatory, as the menu takes the pilot through the necessary steps after having started flight initialization—on Airbus aircraft abbreviated as “FLT INIT.” We used all possible ways of entering information into the OIS, including the keyboard and cursor control units as well as the keyboards hidden inside tables, that can be extended in front of both pilots. Care must be taken when stowing these not to hit the touch screens. If any technical remark is on the dispatch page, it is now possible to click on the item and be immediately directed to the respective page of the minimum equipment list to see what restriction it has or will have for the next sectors. After starting the auxiliary power unit (APU), we were pushed out of our parking position. I turned on the taxi-aid camera system by tapping the “taxi” button on the glareshield, at which point the two cameras—one behind the nose gear and one on the vertical tail—showed their forward views on the PFD. The engines were started one by one in an automated sequence using compressed air from the APU.

Aviation Week evaluation pilot Tim Wuerfel found the big Airbus twin easy to  fly manually, despite its size. Credit: Jens Flottau/AW&ST

We configured the aircraft for takeoff and used the electronic checklist, clicking on the items we had completed. I confirmed with Chandler who would do what if we had to abort the takeoff, as he was the pilot in command and I would be the pilot flying in the left seat. Our aircraft weighed 191,800 kg with a zero-fuel weight of 161,800 kg and 30,000 kg of fuel on board equally distributed between the left- and right-wing tanks, leaving the center tank empty. Takeoff was planned in Configuration 3 with a reduced thrust setting at an assumed temperature of 40C (104F). The resulting speeds were V1 135 kt., VR 142 kt. and V2 145 kt. After I released the parking brake, the big twin started to taxi without adding thrust, as we were comparatively light for an aircraft that will have a dry operating weight of about 155,000 kg in an in-service configuration. On our way toward Runway 32L via taxiway S20, Chandler pushed up the thrust levers to takeoff position for 2 sec. and returned them to idle before the engines could spool up to show the immediate takeoff warning, as we were not on the runway. The warning system also senses any attempt to take off from a runway that has not been calculated and entered in the flight management system and will trigger the relevant alert. It will compare speed to weight numbers that have been entered to rule out wrong inputs and will calculate whether the planned runway is long enough under the entered conditions. As we approached the active runway, an incursion warning showed we were close to entering 32L—in flashing yellow letters on the navigation display. I find this is the best way to attract the pilots’ attention as voice warnings at this point often interfere with communications from the tower. I used the camera view during our lineup and found it helpful with such a large aircraft, which has a wingspan of 64.8 m and length of 73.8 m. The engine indication on the A350 no longer uses N1 or EPR (engine pressure ratio) as the primary value to set thrust, but has a scale of 0-100% of thrust available with engine bleed-air off for takeoff. This was new to me, but it provides an easy understanding of where you are on the thrust scale and how much more is available. I pushed the thrust levers into the “Flex T/O” notch, which gave us the precalculated value for the assumed temperature of 40C of 89.3%. The aircraft accelerated swiftly, and at that point  we could hear the deep sound of the Trent engines. After reaching V1 a steady rotation took us airborne at a pitch of about 8 deg., then 14 deg. as we climbed away.

A switch on the aft center pedestal engages the new automated emergency descent mode. Credit: Jens Flottau/AW&ST

Reducing the thrust to climb power, I used a new feature called DCLB, or de-rated climb thrust. This reduced the power setting to 78%, giving a rate of climb just under 2,000 ft./min. For lower weights, and departures with a low level-off altitude and in high-density areas, it is a welcome feature, as the overpowered twin will otherwise climb at high rates. It reduces stress on the engines, saving life and minimizing the risk of a failure. After a few minutes, we took the derate out, and the engines spooled up to 92%. Flap retraction induced almost no changes in pitch, not even the slight pitch-up during acceleration you can see on other aircraft as the leading-edge devices and flaps come up to the zero position. On entering our reserved airspace block at flight level (FL) 100, west of Toulouse, I flew some turns with 30 and 45 deg. of bank to get a better feeling for the A350-1000. As with all fly-by-wire Airbus aircraft, it has neutral stability up to 33 deg. of bank; above that  it will return to 30 deg. once the sidestick is released. Flying the aircraft manually, with manual thrust control, we turned off the crossbar flight director. This is now actuated by one switch for both pilots, on the glareshield above the two autopilot buttons. Instead, we used the flightpath vector, or “bird,” and a new feature that shows the aircraft’s energy state in the form of chevrons to the left and right of this bird. With changing rates of climb or descent, the pilot can adjust the chevrons to the same level as the bird on the artificial horizon, and the aircraft will climb or descend unaccelerated—a nice feature for manual flight and thrust. During a short unaccelerated, level flight, Chandler turned on the air-data backup mode. This derives its data from engine pickups totally independent of the aircraft’s air-data systems, and it showed our speed within ±2 kt. and altitude within ±20 ft. compared with now crossed-out values on the PFD. We accelerated at FL150 toward the 340 kt. VMO (maximum operating speed) using manual thrust and with the autopilot switched on to see the high-speed protection function. Reaching 340 kt., auto-thrust engaged in idle, immediately reducing speed below VMO. We did not see auto-extension of the speed brakes as deceleration was quick enough. On reaching a speed of 5 kt. below VMO, the auto-thrust disengaged and gave thrust control back to the pilot. The thrust levers were still at climb thrust, so the aircraft accelerated again. To show a more dynamic VMO exceedance, we let the aircraft descend and overshoot the limit a bit faster. This time, we saw a slight automatic speed-brake extension on the flight-control page selected on the SD. With the thrust at idle, we were quickly below the maximum speed again, and the speed brakes retracted automatically without the lever on the center pedestal ever moving.

Rolls-Royce’s Trent XWB turbofan engine has been uprated to 97,000 lb. takeoff thrust to power the A350-1000. Credit: Jens Flottau/AWST

We slowed for some low-speed maneuvers at FL 130 to see a change to the familiar Airbus low-speed protection. As with the high-speed protection, activation of the Alpha Floor protection will disengage auto-thrust and give aircraft control back to the pilots after resolution. Overspeed and low-speed protection would not have activated with the auto-thrust switched on, of course, because a functioning speed control would prevent the pilots from getting into these situations. After air traffic control clearance, we climbed to FL 350 to prepare for an emergency descent and were vectored into an area where the airspace below us was free of traffic. Certified up to a maximum operating altitude of 41,450 ft., the A350-1000 is the first aircraft able to use the new feature developed by Airbus: the automatic emergency descent (AED). This was developed for two purposes. It will assist pilots during execution of an emergency descent and provide a last safety net in case there is no reaction by the crew. The second objective is a response to the 2005 Helios Airways Flight 522 accident, in which a Boeing 737-300 crashed in Greece after loss of control due to hypoxia. All 121 people on board died when the aircraft finally crashed due to fuel starvation. Airbus believes reaction time is the key element in the event of rapid decompression of the cabin. It is my impression that airlines in recent decades have reduced pressure on crews to immediately initiate an emergency descent, due to the possible risk of other traffic below and injuries in the cabin. They ask pilots to evaluate if a full emergency descent is necessary or if a quick descent will do. The AED could provide assistance to accelerate things. At today’s cruising levels, pilots have 10-45 sec. to put masks on and supply themselves with oxygen. After that, the TUC—time of useful consciousness, when we are able to help ourselves—is over. To arm the AED, the pilot pushes a guarded switch built in on the left side of the speed-brake lever on the aft center pedestal. And, after informing air traffic control, we did just that—“EMER DESCENT ARMED” appeared in red on the PFD. The descent is then initiated by pulling the speed-brake lever. The flight mode annunciator shows the “EMER DES” mode. The traffic collision avoidance system (TCAS) is automatically set to “below,” showing traffic in the proximity on the navigation display down to 9,900 ft. below our position. If the aircraft is on a heading to avoid weather, it will stay on that heading during the descent. If it is in NAV mode on an airway, it will step to the right side by 2.75 nm and follow a parallel track to avoid traffic on the same airway at lower levels. With the AED, there are only two actions required from the pilot flying to start the descent instead of five in the present procedure. Also, ATC is informed as the transponder code changes to 7700. We notified the controller in advance about the automatic change of code and reverted to the previous setting after confirming we were in the steep descent only for the demonstration of the system. As we had been cruising at FL 350 and Mach 0.85, the system asked for acceleration to VMO/MMO—5 kt. Consequently, as thrust came back to idle and speed brakes extended, our aircraft dived to a rate of up to 9,000 ft./min to accelerate to target speed. This happened smoothly, so people and service equipment could not be tossed around the cabin. As we accelerated to the MMO of Mach 0.89 -5 kt., the rate of descent reduced to about 5,000 ft./min to keep inside the speed limit. The target altitude appeared in the altitude window on the glareshield. It will typically be either 10,000 ft. or the minimum off route altitude (MORA) within 40 nm of the aircraft’s position in any direction if higher than that. The MORA is derived from the enhanced ground proximity warning system. In our case it was 13,200 ft., as were close to the Pyrenees on the border between France and Spain. If the TCAS were to sense a conflict with other traffic during descent, leading to a traffic advisory, the respective mode would be armed. If it came to a resolution advisory that asked for correction, the emergency descent mode would disengage, and the TCAS mode would engage and follow the advisory. Once “clear of conflict,” the system then reverts to basic modes such as vertical speed. If the crew wanted to continue the emergency descent, it would have to rearm and reengage the system. When providing the last safety net, if there has been no crew reaction following a depressurization, the AED system will arm itself when cabin altitude rises above 14,000 ft. The PFD will show “AUTO EMER DES IN 15 S” and start to count down. If there is no input by the pilots, the system will then engage and start the descent as described above. It will complete the descent at the calculated flight level and revert to basic modes, keeping speed, heading and altitude. It is assumed that if there is no reaction from the flight crew due to a lack of oxygen, the pilots will regain consciousness as the oxygen supply rises at lower altitudes. This was confirmed by experts at German aerospace center DLR, provided the pilots are not exposed to hypoxia for a prolonged time. It is worth noting the pilots can interact with the sequence at any time. Whether initiated by crew action or automatically, any input by the pilots is possible and will stop the otherwise automated sequence. In most training scenarios in simulators today, pilots are accustomed to maintaining the current speed in an emergency descent following a simulated rapid decompression. This is done because it is assumed the aircraft’s structure might have sustained damage leading to the decompression and should not be stressed by higher speeds during the recovery. I am sure this will be subject to discussion, and we will see how airlines integrate the latest Airbus development into their training and whether they want pilots to keep current speed or opt to reduce the time to lower altitude by allowing acceleration. Using the AED, we reached an altitude of 14,000 ft. in less than 4 min. After the impressive maneuver, we returned to Toulouse and flew around some small, isolated thunderstorms that had developed in the heat of the afternoon. Chandler and I prepared a satellite landing system (SLS) approach to Runway 32L. The A350 is the first widebody with a satellite-based augmentation system embedded in its design, allowing this approach type at an accuracy of a Category I instrument landing system (ILS) without any ground equipment. The way the approach is displayed on the PFD is just like an ILS, which also is Airbus’ goal for other approach types, except that the identification in the lower left corner has a different format and the letters “SLS” in the lower right corner denoting the type of precision approach. After almost 2 hr., our A350 weighed 179,500 kg with 17,700 kg. of remaining fuel. With flaps fully deployed, that resulted in a VLS (lowest safe speed) of 128 kt. and a resulting VAPP (approach speed) of 135 kt. with a wind from 300 deg. at 17 kt. We planned to leave the runway at taxiway S8, giving us a landing distance available of 2,362 m (7,750 ft.). We activated the brake-to-vacate (BTV) function by clicking on the respective point in the menu and on the intersection on the airport chart. I flew the aircraft manually on final approach, with manual thrust. Again the response of the -1000 to my input was pleasantly direct given its length and weight. I worked to find the right power setting between 20-30%, with winds slightly from the left and some gusts. The view from the cockpit seemed rather high as I broke the descent rate a little less than 40 ft. above ground. With our low weight, it was just early enough to end up in a smooth touchdown slightly in front of the aiming point. As Chandler had told me, the nose gear was almost landing itself softly. The idle reverse-thrust setting slowed us down, and it was as late as 80 kt. when the autobrake added some pressure to bring the aircraft down to 10 kt. shortly before the turnoff to taxiway S8. I stepped on the brake pedals to disengage the BTV system and turned off the runway. Chandler reminded me to slow down a little for the next 90-deg. turn to the left as the aircraft had already gained speed with idle thrust. I checked the groundspeed indication from time to time as we rolled back to our parking spot, as I had underestimated the taxi speed from the high cockpit view. At the parking spot, we kept the engines running until the flight-test engineers informed us they had completed their checks and the cooling time they asked for was over. With the APU running already, we shut down the Trent engines and completed the short parking checklist. Those about to be trained to fly this aircraft have every reason to look forward to the experience. Every pilot that has flown a sidestick-controlled Airbus will not only feel at home in the cockpit but also find manual handling of the A350-1000 easy. The aircraft can be flown accurately and with a little delay in reaction, but it is agile for its size and weight. The cockpit is Airbus’ most advanced yet and the A350-1000’s layout, size, 6,000-ft. pressure altitude and low noise level make it the type of workplace pilots will welcome.