Can Airbus fly-by-wire flight control technology make the world’s largest airliner as easy and safe to fly as one of the European manufacturer’s ubiquitous narrowbodies? Since Airbus launched the 555-seat A380 six years ago, that question has been at the forefront for both pilots and passengers.
More than 50 airline pilots have flown the A380, getting an early taste of how this ultra-large aircraft operates and providing Airbus with invaluable feedback from an operator’s perspective. Now Airbus has put its technology to the test by inviting Flight International and other journals to evaluate the A380, in the final stages of certification flight testing at Toulouse in France.
Despite well-publicised production delays, Airbus says it is on track to complete certification flight testing on the A380 in October. Route-proving will take place in November, and European type certification is expected in December. Four long-range flights have already been conducted with 474 passengers and 26 crew on board to work out the kinks in cabin and entertainment systems.
Flight International's Mike Gerzanics was accompanied by Airbus test pilot Peter Chandler for the in-flight handling demonstration
So far this year, Airbus has completed hot weather testing, accomplished in July in Abu Dhabi where temperatures up to 46°C (115°F) were encountered. A deployment to Medellin, Columbia showed the A380 could handle equatorial heat and elevations of 7,000ft (2,130m) above mean sea level. At the other extreme, operations in temperatures down to -29°C were demonstrated during a stint at Iqaluit, Canada. Icing certification tests have also been completed, and included both artificial shapes trials and natural icing encounters.
Designed to accommodate 555 passengers in a typical three-class configuration, the A380 seats 35% more people than its nearest flying competitor, the Boeing 747-400, Airbus calculates. While the new 747-8 Intercontinental promises to carry 450 passengers in a three-class configuration, narrowing the gap, in March this year Airbus showed the double-decker A380 could safely carry many more passengers in a high-density configuration. A cabin evacuation test confirmed that 853 passenger and 20 crew could exit the A380 in less than 90s using only half of the exit doors. While debate will continue over which of these aircraft is more economical, or represents the best value, Airbus to date has garnered orders for 143 passenger and 25 freighter versions of the A380.
The A380 may be an all-new aircraft, but it is undoubtedly an Airbus. Since the introduction of the A320, all Airbus aircraft have incorporated several major common features, including fly-by wire (FBW) flight controls and a common flightdeck configuration. In these two regards the A380 appears just as expected, but look beneath the surface and a whole host of innovations is revealed.
The A380’s flight controls are hydraulically powered, as with previous Airbus aircraft, but there are only two hydraulic systems. The Green and Yellow systems are powered by engine-driven pumps and operate at 345bar (5,000lb/in2), instead of the 207bar systems in prior Airbus aircraft. The higher operating pressure significantly reduces weight, saving upwards of 800kg (1,760lb) compared with an equivalent 207bar system. Deletion of the third hydraulic circuit (Blue in other Airbus aircraft) further reduces weight, but could have compromised operational safety were it not for the electrical backup hydraulic actuators (EBHAs), unique to the A380, that can operate both the upper and lower rudder, half the elevators and a spoiler and two ailerons on each wing. The EBHAs function as conventional control-surface actuators until there is a hydraulic system failure, when they operate independently, powered by the aircraft’s AC electrical system. Further, one control surface in each axis is powered by the essential AC bus, which can be powered in flight solely by the ram air turbine (RAT). The standalone EBHAs and RAT provide a high level of redundancy while allowing for significant overall weight savings.
At take-off the aircraft weighed 390t, which included 90t of fuel and 1.8t of passengers
The expansive flightdeck, located at mid-level between the two cabin decks, gives a pilot eye height of 7.2m, approximately halfway between the 777’s 5.9m and 747’s 8.7m. The overall layout reflects previous Airbus cockpits, but on a larger scale. In addition to the pilot and co-pilot seats, the flightdeck comes standard with two additional full-size seats aft, with provisions for an optional fifth seat. The extra area provided by the large instrument panel and pedestal allows the addition of two extra liquid-crystal displays (LCD) as well as the onboard information system (OIS) screens. Each pilot is provided with a primary flight display (PFD) and navigation display (ND), while there are two shared integrated standby instrument system (ISIS) displays for back-up navigation. In the centre of the panel is the engine/ warning display (EWD), while three additional screens are positioned between the instrument panel and pedestal: two multi-function displays (MFD) outboard and a centre system display (SD).
Unique to the A380, two pedestal-mounted keyboard and cursor control units (KCCU) provide an efficient interface between man and machine. Each features a QWERTY keyboard, unlike the alphanumeric keypad typical in most glass cockpits. They also incorporate a track ball and scroll wheel to manage the associated displays – each KCCU only controls the respective pilot’s ND and MFD, as well as the common mailbox that is used for datalink communication with air traffic control. The KCCU interface allows for graphical en-route flight planning, a powerful capability not found on other Airbus aircraft.
Three screens are positioned between the instrument panel and pedestal: two multi-function displays outboard and a centre system display
Electronic centralised aircraft monitor (ECAM) data are shown on the central EWD and SD and controlled solely by a dedicated panel aft of the throttle quadrant. The “smart” electronic checklist, presented on the EWD, automatically senses system status, checking off that item for the crew. Non-sensed items, however, must be “checked” using the ECAM control panel. The 777 features a smart checklist, navigated via a touchpad cursor control device (CCD), while the Dassault EASy and Gulfstream PlaneView integrated flightdecks I have flown allow the crew to interface with numerous avionics systems via a single input device – a step not taken by Airbus.
Between each side console and the forward instrument panel are the large left and right displays for the OIS, which is still under development and promises to provide a full electronic flight bag (EFB) capability for the A380. The OIS will allow for a paperless cockpit by providing minimum equipment and configuration deviation lists, aircraft flight and crew operating manuals, and navigation and weather charts digitally. In addition, weight and balance and performance computation tools will allow for onboard calculation of critical operational parameters.
The tray table's full-size keyboard felt substantial and will greatly ease the tasks of data and text entry
The system will not be fully operational at entry into service. Initially A380s will be equipped with three laptops – one for each pilot and a back-up. The aircraft will have an electronic library from the start, but with paper airport charts and quick-reference handbook. The OIS was not operational on our demonstration flight aircraft, but provisions for its installation had been made. Located in each pilot’s pull-out tray-table is a keyboard and touchpad CCD to control their respective systems. The full-size keyboard felt substantial and, in the paperless cockpit, will greatly ease the tasks of data and text entry.
While not markedly larger dimensionally than the 747-400, the A380’s double-decked fuselage and thick-rooted wing give it an imposing ramp presence. During the walk-around inspection of MSN001, Airbus test pilot Peter Chandler pointed out some of the aircraft’s features, including the wing’s lofting, which increases ground clearance for each of the four 2.95m (116in) fan-diameter Rolls-Royce Trent 900 engines. The twist of the inboard wing section is marked, with the trailing edge dropping rapidly from the inner engine nacelle to the fuselage. When viewed from behind this gives the A380 a “gull wing” appearance.
The Pratt & Whitney Canada PW980A auxiliary power unit (APU) was running during our walk-around, but its location in the tailcone, high above the ramp, and acoustic design softened the noise so that a normal conversation could be conducted near the tail. The landing-gear layout is similar to that of a 747, except the body gear on the A380 each have six wheels. The A380’s 22 wheels, four more than on the 747, help distribute weight to give it a lower pavement loading than other large aircraft. The body gear’s rear axle is steerable, improving ground manoeuvrability. Airbus has demonstrated a 180° turn on a 60m-wide runway – slightly more than its next largest aircraft, the A340-600, which requires 59m.
Once on board the aircraft, access to the flightdeck was via a four-step stairway from the main cabin deck. Aircraft start, taxi, take-off and climb to altitude were conducted by Airbus chief test pilot Jacques Rosay and several of the pilot journalists taking part in the demonstration flight. Alignment of the three air data inertial reference systems was automatic using GPS and took approximately 7min. Flight management system (FMS) initialisation and route entry were similar to other glass-cockpit aircraft. Take-off performance data were manually loaded from a sheet prepared by ground operations personnel. The OIS has the capability to provide this, but system architecture only allows data to flow from the aircraft to the OIS. Data transfer from the OIS to the aircraft is forbidden.
Pre-start flows were straightforward, and the aircraft was pushed back for engine start. As with the A340-600, both engines on a wing are started simultaneously: engines 3 and 4 were started first, followed by 1 and 2. Unlike in other Airbus aircraft, the engine start selector is now on the overhead panel, not the pedestal. With its starter engaged, the master lever for each engine was placed to the “on” position. The dual-channel full-authority digital engine control managed the start sequence, providing fuel and ignition at the appropriate time. Each engine reached idle in less than 60s. Peak exhaust-gas temperature was less than 410°C on each engine, well below the redline limit displayed on the ECAM. With all four engines running, the APU was shut down and a flight-control check conducted.
Flaps were set to Config 3 (slats 23°, flaps 26° and ailerons drooped 5°) and pitch trim set to 4° up before taxiing for take-off from Toulouse’s runway 32L. The A380 is the first Airbus that does not have a tailplane trim wheel on the centre console. Fitted to previous FBW Airbuses to give pilots a manual reversion option in the event of a full failure, the wheel is replaced by a pitch trim switch on the aft end of the pedestal.
For the initial take-off, a reduced thrust setting was programmed by selecting “Flex 50” on the FMS, which told the engines to assume an outside air temperature of 50°C, compared with the ambient temperature of 18°C. The Trent engines are limited to 78% N1 low-spool speed during take-off until 45kt (83km/h) is achieved, to reduce fatigue on engine components. This limit will be reduced to 35kt on customer aircraft, and has a negligible impact on take-off performance, says Rosay.
At take-off the aircraft weighed 390t – well below the standard 560t maximum take-off weight (MTOW) – which included 90t of fuel and 1.8t of passengers. This implies an operating weight empty (OWE) of 298.3t, but MSN001 is configured for flight test and likely has 10-20t of ballast and test equipment on board. For production aircraft, Airbus is projecting a typical OWE of 277t.
For the take-off and first portion of the climb to altitude I occupied a seat on the upper deck of the passenger compartment. Observed acceleration during the take-off roll was smooth, with the ECAM showing that only 75% of available thrust for the ambient conditions was used for the reduced-power take-off. The Trent 900’s standard thrust rating for the A380-800 is 70,000lb thrust (312kN), but for our flight MSN001’s engines had the 72,000lb thrust rating that is offered with the optional 569t MTOW.
Ground roll and time to lift-off, as recorded by the flight test engineer Fernando Alonso, were 1,345m and 37s respectively. Distance and time to clear a 35ft obstacle were computed at 1,825m and 43s respectively. Final performance numbers have not been released, but at MTOW Airbus projects a balanced-field take-off distance of 2,990m at sea level and ISA+15°C.
During the climb to FL300 (30,000ft), the engine anti-ice was manually turned on when entering clouds at FL090. The number 2 engine nacelle anti-ice valve initially stayed closed, generating an ECAM message. While there is little remarkable about this, the corresponding “Avoid icing conditions” limitation message displayed on the lower portion of the PFD was notable. The bottom quarter of each PFD is permanently reserved to display aircraft configuration (slat/flap/trim/landing gear position), memos and limitations. After the valve was fixed, the ECAM message and limitation memo both went away.
Also during the climb, we were able to explore a new capability provided by the vertical display (VD) shown on the lower quarter of the ND. The VD displays enhanced ground-proximity warning system terrain data and weather radar returns along with FMS vertical profile information to clearly show upcoming obstacles. The display gave a pseudo three-dimensional view of upcoming weather, providing a profile view to augment the map display’s plan view. One neat feature is the ability to slew the vertical-profile line off the aircraft’s track, allowing the crew to refine their view of upcoming weather.
The aircraft was levelled off at FL300 approximately 16min after brake release. About 8t of fuel had been burned from engine start to level-off. For a standard day, Airbus shows an initial cruise altitude of approximately 42,000ft for our take-off weight, just below the maximum certified altitude of 43,000ft. At the standard 560t MTOW, an initial cruise altitude of just over 35,000ft is indicated. While level at FL300 a cruise speed of Mach 0.80 was held, well below the projected cruise speed of M0.85.
Flight control laws
Indicated airspeed was 305kt, with a corresponding true airspeed of 472kt. Total fuel flow was approximately 13,000kg/h. With 555 passengers Airbus projects a range of 14,800km with a 5% fuel reserve and 370km-distant alternate.
The A380 may be an all-new aircraft, but is undoubtedly an Airbus
While seated in the cabin, I found the ambient noise level to be fairly low, especially considering the interior of MSN001 lacked production acoustic insulation and cabin interior sidewalls. According to Airbus, preliminary acoustic tests show the A380 to have an interior quieter than its A340-600 stablemate, 50% quieter than the 747-400 and below the stated noise level targeted for the 787.
One of the hallmarks of Airbus FBW aircraft has been the incorporation of active envelope protection into normal flight control laws. The A380 continues this with features familiar to any FBW Airbus pilot. At FL300 with the autopilot off in level flight, the flying pilot selected climb power with the thrust levers. Shortly after passing the maximum operating Mach number of 0.89, the aircraft began a gentle pitch-up to prevent further exceeding the published Mmo limitation. This same manoeuvre was later repeated below FL200 where the maximum operating speed (340kt) was exceeded. Again the aircraft started a gentle pitch-up to arrest the Vmo exceedance. In both cases, the thrust remained at the previously set value. All Airbus FBW aircraft have autothrottle, or autothrust, and for slow-speed conditions the system will automatically apply take-off/go-around (TO/GA) thrust to prevent the aircraft from exceeding a safe angle of attack (AoA). In my opinion, mechanising the autothrust to retard power in an overspeed would slow the aircraft more rapidly while maintaining an assigned altitude, especially critical in reduced vertical separation minimum airspace. Airbus points out that if the autothrust is engaged then this function is activated, but that the autothrust will not engage automatically at high speed.
At the lower end of the A380’s operating envelope, Airbus has embedded control-law protections to prevent a stall. During flight test, the A380 showed itself to be docile at slow speeds. In the clean configuration the stall speed is defined by attaining “deterrent buffet” – a buffet amplitude so large the aircrew cannot read the flight instruments. For all other configurations, the stall is defined by a G break, the point where the load factor first drops while holding aft stick. While flying the aircraft at FL140 with 73t of fuel, Config Full (slats 23°, flaps 33° and 10° of aileron droop) was selected with landing gear down. In idle power with full aft stick, a maximum AoA of 14.2° was reached at 118kt, quite a low speed for such a large aircraft.
In the roll axis, the A380 has the same handling qualities and envelope protection as other FBW Airbus aircraft. Roll rate is commanded by lateral displacement of the sidestick. As well as moving the three ailerons and six of the eight spoilers on each wing to attain the desired rate of roll, the flight control system automatically commands rudder deflection to minimise sideslip. Unlike the 747 and 777, which have two ailerons per wing (one mid-wing and one near the tip) all three ailerons on the A380 are located outboard of the outer engine pylon. At speeds above 240kt indicated the outermost aileron is locked out, the remaining two more than sufficient to attain desired roll rates. Each aileron is commanded independently and, due to structural aeroelasticity, may be out of step with its wing mates – deflecting up, for example, while the wing itself is rolling up. All of this is transparent to the pilot, with the system providing control in the roll axis that is precise and predictable.
Where Airbus has significantly changed its design philosophy is in the yaw flight-control laws. With the A380, Airbus has implemented a direct control of the sideslip angle made possible, for the first time on an Airbus aircraft, by the three sensor vanes mounted on the nose that measure directly the sideslip value.
In most conventional aircraft a constant rudder displacement will generate a corresponding roll rate in the same direction – stepping on the right rudder will cause the aircraft to roll to the right, for example. Stepping on the rudder pedal in the A380 commands a sideslip angle determined by the flight control laws. At slow speeds in Config Full up to 15° of sideslip can be commanded, while at high speeds in a clean configuration only 2° of sideslip can be commanded. As on other FBW Airbuses, the resultant sideslip does not generate a constant roll rate; rather a constant bank angle approximately equal in magnitude to the commanded sideslip held – stepping on the left pedal to yaw the nose 4° to the left commands a constant 4° left bank angle.
Airbus felt roll rates generated by yawing motions were undesirable, with two exceptions. One is in the event of an engine failure, where the asymmetric thrust causes yaw, and corresponding roll, into the dead engine. These yawing and rolling motions provide valuable cues to help the pilot correctly diagnose the loss of an engine. For decrabing, the flight control law aims at decoupling the yaw and roll axis so that yawing the nose to align with the runway axis generates no roll.
This flight control theory was put to the test at FL140 as I simulated a go-around from the Config Full approach to stall. After calling for a go-around, the thrust levers were advanced to the TO/GA detent, landing gear retracted and flaps set to Config 3. Accelerating through 140kt, Chandler rapidly pulled the number 4 engine thrust-lever to idle. The nose yawed to the right and the aircraft settled into a 4° constant right bank angle. I levelled the wings using the left rudder and then shifted my attention to the PFD.
The sideslip indicator below the bank-angle pointer on the PFD had, because of the asymmetric-thrust condition, become a sideslip target. This target commands a minimum-drag slip angle, not zero sideslip, to minimise spoiler deflection and improve engine-out performance. For our conditions, centering the sideslip target required a third of available left rudder deflection and allowed 2° of nose-right sideslip. Checking the flight controls page on the ECAM’s lower display showed that all spoilers were indeed retracted. As with the A340-600, I found the A380’s response to a potentially disastrous loss of thrust at low speed to be quite benign, greatly easing pilot workload.
Handling-qualities work at medium altitudes complete, radar vectors were followed for pattern work at Toulouse where the active runway was 32L. After seven touch-and-go landings had been performed by the several pilots onboard, I climbed into the left seat for my first approach in the world’s largest passenger aircraft. Low clouds had moved into the airport area, necessitating flying a radar box pattern for vectors to an instrument landing system (ILS) final approach. For the first pattern I used the autopilot to manoeuvre the aircraft. Autoflight modes and procedures are identical to other Airbus aircraft, and the autopilot and autothrust captured and held all commanded headings, altitudes and speeds.
On base leg, Config 1 was selected and an “S” speed of 180kt held. On a dogleg to final, Config 2 was selected when the ILS glideslope came alive. After localiser capture the landing gear was extended, and Config 3 was selected just before capture of the glideslope at 2,500ft above the ground. I clicked off the autopilot and manually followed the flight director’s split cues to track localiser and glideslope. Autothrust maintained an approach speed of 136kt, letting me concentrate solely on the flight director. Pitch attitude on final was 2.5° nose-up, a lower angle than experienced in the A340-600. At 50ft radar altitude I began a slow flare, increasing pitch attitude to 4.5°. Immediately after the 20ft altitude callout, “retard” was announced and I moved all four thrust levers out of the climb detent to the idle position which disengaged the autothrust. Holding a constant pitch attitude, the aircraft gently settled on to the runway at a sink rate of less than 2ft/s.
Once on the runway I was able to lower the nose gear smoothly to the ground. With the aircraft in a three-point attitude, Rosay retracted the spoilers and set the flaps to Config 3 for the touch-and-go. I advanced the thrust levers to a mid position, allowing the engines to spool up before moving the levers to the TO/GA detent.
The engines rapidly accelerated to 98.5% thrust. Rosay called “go” at 140kt and a light aft pull on the sidestick allowed me to capture a take-off attitude of 12.5°. With the landing gear retracted, a turn to crosswind was initiated 400ft above ground. There were no changes in pitch control forces during flap retraction as the aircraft accelerated to 250kt in the climb to downwind at 4,000ft.
I hand-flew the aircraft for the entire second approach, autothrust accurately maintaining the managed speed for each configuration. Overall I found the A380 quite responsive in the radar traffic pattern. On final approach I found the pitch control laws allowed me to track the glideslope precisely. Roll control was equally precise, allowing extremely fine inputs to keep the super-jumbo dead-centre on the localiser. The flare was initiated at 50ft radar altitude, with the thrust levers retarded to idle just below 20ft. The resulting touchdown was at a slightly higher sink rate than the first, but the multi-bogie main landing gear smoothly absorbed the extra energy. Touchdown de-rotation was much smoother than when I flew the A340-600, due to the A380’s lower pitch attitude at touchdown and shorter distance between the main and nose gear.
With the nose gear on the runway, I deployed the A380’s two thrust reversers. At 100kt I applied toe braking to further slow the aircraft. The thrust reversers were stowed slowing through 70kt, and toe braking alone brought the aircraft to 20kt ground speed. Airbus is introducing a “brake to vacate” (BTV) autobrake function on the A380, but the system has not been tested and was not available for evaluation. BTV will enable the pilot to specify the target runway exit ahead of landing by using the KCCU to click on the airport map displayed on the ND. On landing, the autobrake system sets the appropriate amount of braking to slow the aircraft evenly for exit at the specified taxiway.
As we slowly taxied down the runway, Rosay selected the onboard airport navigation system display by selecting the “zoom” position on his ND map range selector. This brought up a detailed airport moving map depicting the aircraft’s position. The increased situational awareness provided should help prevent runway incursions and wrong-runway take-off attempts. I slowed the aircraft to 10kt ground speed for the 90° turn off the runway. The external and taxiing camera system (ETACS) allowed me to judge each landing gear’s location on the tarmac, while the tiller-controlled nosewheel steering allowed accurate tracking of taxiway centrelines.
Of all the large aircraft I have flown, the McDonnell Douglas DC-10 stands out as being the most uncomfortable to taxi. The nose gear is more than 6.5m behind the pilot’s seat, and 90° turns require you to taxi well past the centreline of the desired taxiway, at times placing the cockpit over the verge of the taxiway. Several 90° turns showed the A380 to be an easy aircraft to manoeuvre on narrow ramps and taxiways – qualitatively on par with a 777-200 and easier than an A340-600 or the DC-10. While I did find the ETACS useful, a seasoned jumbo pilot will have no trouble safely taxiing an A380 without it.
During the 3:35 block-hour flight I piloted the A380 at the extremes of its speed envelope and, as with other Airbus FBW aircraft, it displayed predictable and safe handling qualities. I found the aircraft to be quite responsive in the traffic pattern. While guiding the 747 Classic down final approach can require some finesse at times, the A380 crisply responded to control inputs. I was able to fly the A380 with the same precision as I could the 777, but I must admit to preferring the fly-by-wire Boeing’s conventional yoke to the A380’s uncommunicative sidestick. As with the A340-600, I found the A380 responded quite benignly to a simulated engine failure, a direct benefit of Airbus’s FBW flight control philosophy.
Both airborne and on the ground, the A380 felt and flew like a smaller aircraft. Pilots transitioning from other Airbus types will immediately feel at home on the flightdeck, and will find new features such as the onboard information system, airport navigation system and vertical display to be useful. Assuming the A380 meets its range and payload goals it will soon be safely and efficiently whisking upwards of 500 passengers to distant points on the globe. Certainly, from a handling qualities point of view, the aircraft seems more than up to the task. ■