Peter Henley/HAMBURG
The 124-seat A319 is the smallest of the Airbus Industrie family of airliners, featuring the same basic flightdeck and similar handling characteristics to all the other Airbus fly-by-wire (FBW)aircraft.
A "shrink" derivative of the 150-seat A320, the A319 is offered with the same engines as the larger model, but both the CFM International (CFMI)CFM56-5A and International Aero Engines (IAE) V2500-A5 options are flat-rated to 98kN (22,000lb) thrust in their basic specification, with a 105kN option.
The commonality happily extends to the A319 cockpit which is identical to that of the A320 and A321, and the three have a common pilot type-rating. Indeed the cockpit is the same for the widebody A330 and A340 except that the latter has four power levers and system-management panels allied to the four engines. Pilots can therefore readily be cross-qualified between a widebody and narrowbody Airbus.
The Airbus rationale behind using an electronic flight-control system is that it provides capabilities which conventional systems could not. Airbus claims safety improvements in protection against inadvertent overstressing of the airframe, over-speed, stalling, and windshear. Just as importantly, it allows crews to demand maximum performance from the aircraft without fear of stalling or exceedances in sudden emergencies. Fly-by-wire, says Airbus, improves handling and allows a better-designed working environment.
Such radical thinking has a marked impact. The pilot of an FBW Airbus controls the aircraft through a sidestick mounted on a side console outboard of each seat. The control-surface response is not directly proportional to stick movement as it would be with a conventional system. Differences such as these have inevitably begged questions about the "user-friendliness" of an FBW Airbus. Why not, as Boeing has done with the 777, use an FBW system which looks and feels like the one pilots are used to? How difficult would it be for a pilot out of flying-training school to adapt to a different concept? In the reverse case, how would an FBW-Airbus-rated first officer face up to flying, say, a Boeing 767, with its conventional yokes, etc, on promotion to captain?
There are now probably more than 5,000 Airbus-qualified pilots worldwide, but there is still some apprehension, fascination and mysticism about flying the computer-dominated Airbus. Since I had no FBW experience other than some time which chief test pilot William Wainwright had found for me in his busy schedule to introduce me to the concepts on a development simulator, I was able to find out what adjusting to an FBW-Airbus was like.
The first impression on cockpit entry is one of light, space, symmetry and the almost clinical appearance of the uncluttered light-grey panels. The absence of control wheels and columns is, of course, immediately apparent: there is space where they would be located in a conventional aircraft. The two sidesticks are mounted outboard of the seats where they come readily to hand. The outboard arm-rest of each seat is wide, flat and upholstered, to form a platform for the pilot's "flying" arm to rest upon. The sidesticks are shaped to provide a comfortable and effective grip, a little like the grip of a competition target-pistol. Each grip has a finger-operated transmit trigger switch and a prominent red thumb-operated button for autopilot disconnect and to give that sidestick authority over the other - eg: to allow one pilot to take control, or in the case of a jammed control-surface.
The centre console is broad and houses the flight-management displays and keyboards, plus the navigation and communications controls. The power-lever quadrant is in the centre of the console with a manual pitch-trim wheel either side of it. Access to the pilots' seats is unusually easy, because there is no control-column in the way and the seats swing outboard at the rearward limit of their travel. They are adjusted fore, aft and vertically by switch-controlled electric motors. There is room for a flight-bag outboard of each seat. The eye-position indicator is built into the trim of the centre windscreen pillar, and the field of view is good, with each pilot able to see the wingtip on his or her side.
The absence of control columns allows each pilot to be provided with a fold-away work-surface which stores beneath the instrument panel, but can be pulled out and unfolded to form a table to take a meal tray or documents. Each pilot also has a pair of foot-rests fitted to the lower edge of the instrument panel to give feet-up relaxation for the pilot not flying. Hence, the flightdeck of the FBW Airbuses, with their "desk" for each pilot and an array of computer services, has moved closer to an office-like environment than that of any other aircraft.
The computer equipment is a Sextant Avionique electronic flight-instrument system (EFIS), which has six identical 185x185mm cathode-ray tubes (CRT). A primary flight display (PFD) and navigation display (ND) are situated side by side in front of each pilot. The PFD is much like those of other manufacturers, except for minor differences in the positioning of flight-mode information relative to the attitude information. It is easy to forget, however, that it was Airbus which introduced the airspeed-vector arrow to counteract the lack of trend perceived to be provided by "tape" airspeed indicators.
The other two CRTs are mounted one above the other on the centre panel. The two vertically mounted CRTs are for the electronic centralised aircraft monitor (ECAM), Airbus' version of an engine indicating and crew alerting system.The upper display shows primary engine indications in analogue/digital format, fuel quantity, flaps/slats position and has a memo segment for crew messages. The lower CRT is used for systems synopsis pages: manual selection of one of 12 displays can be made or, in the case of a malfunction, the relevant pages appear automatically. Each pilot has an EFIS controller outboard of the glareshield control panel, while there are common ECAM controls at the forward end of the centre console. Display formats can be switched as required between CRTs to compensate for any screen failure. There is a set of conventional standby instruments - altimeter airspeed indicator (ASI), attitude director indicator (ADI) and radio magnetic indicator (RMI).
The overhead panel houses the controls for the aircraft systems - fuel, hydraulics, air conditioning, auxiliary power-unit (APU) and the fire control for both the engines and the APU.
The cockpit philosophy is "lights out" for normal system operation and "need to know" for information display, to reduce the crew instrument-scanning chores to a minimum, although full indications for engines or systems can be called up as required. The ECAM monitors the systems and alerts the crew to any malfunction through audio and visual attention-getters, while automatically displaying a relevant system synopsis with malfunctions highlighted and relevant corrective action displayed.
The engines have full authority digital engine control (FADEC) and consequently are fully protected during starting. Engine starting normally uses bleed air from the APU and is automatic from the point at which the pilot selects the ignition on and moves the starter switch to START on the centre-console engine mode-selector panel. In addition to controlling the start the FADEC will automatically abort the sequence if there is a hot start, hung start or failure to light up.
The aircraft flown by Flight International was a production A319 destined for Swissair (registration D-AVYZ/HB-IPS) undergoing its production flight-test schedule at Daimler-Benz Aerospace Airbus' plant at Finkenwerder airfield in Hamburg, where the type is assembled alongside the A321. Swissair operates all three members of the A320 family, and will introduce the A330-200 in 1998. This aircraft was complete save for passenger-seats and carpets (and consequently had a forward centre-of-gravity), held 15,000kg of fuel and weighed 54,200kg for take-off.
Accompanying me for the flight were Wainwright and flight-test engineer Dominique Jerome. The weather at Finkenwerder was good, and we used runway 23 with a surface wind of 280¼ 15-20 kt and 9¼C temperature.
The A319 was straightforward to taxi, using the small hand-wheel outboard of the side-stick to operate the electrically controlled nosewheel steering. The wheelbrakes were smooth and progressive. Flap position 2 (22¼slats/15¼ flaps) was set for take-off and the full power of the CFM56 engines was used. The engines were slow to "spool up" initially but then accelerated more rapidly to maximum power. The aircraft was easy to keep straight, to rotate and to establish in the climb.
The area of greatest interest to a pilot flying the Airbus for the first time is, of course, the fly-by-wire controls. Control-surfaces are conventional and they are all hydraulically actuated and electronically controlled except for the rudder, which is mechanically controlled; but even here, yaw-damping, turn co-ordination and trim are electronically managed. Pitch-trim is provided by the variable-incidence tailplane, electronically controlled but with mechanical back-up. Pitch control is provided by conventional elevators and roll control by ailerons and spoilers. A total of seven computers processes the pilot's control commands.
The ability of computers to perform faster, more consistently and more accurately than a human and to perform more complex functions is extensively exploited in the A319. The pilot continues to control the aircraft, to manage the flight and make the decisions; computer technology helps him do it.
For example the latest Airbus versions, including the A319, have feed-back which damps aircraft response to side-stick inputs and to gusts, thus giving a softer, smoother ride.
The same system also provides auto-stabilisation. The first characteristic which becomes apparent to the pilot is that the aircraft is continuously retrimmed automatically. This means that the A319 will behave hands-off (stick-free) like any other properly trimmed aircraft, but the pilot is relieved of the task of trimming. There are no stick-mounted trim switches provided for pitch or roll and the pitch-trim wheels are used solely to set the correct trim for take off and as an emergency mechanical back-up.
The side-stick works in the conventional sense and produces a rate of aircraft response which feels right to a pilot accustomed to a conventional aircraft. A comforting feature of the system is that the apparent response to the control and the feel remain constant throughout the flight envelope.
The A319 flying-control computers will protect the aeroplane from stalling, dangerous angles of bank, low speed and overspeed. Airbus, however, emphasises that the FBW flight-envelope-protection does not merely protect, but enables pilots to achieve maximum performance when essential, knowing that they can fly the aircraft up to the limits and stay there until the danger is past, without fear of an exceedence.
To check the alpha-protection, the side-stick was held fully back at 250kt with power set manually for level flight. Initially the pilot's full nose-up demand is modified to ensure that the clean-wing limit of +2.5g limit is delivered but not exceeded (+ 2g with flaps selected). Once a maximum angle of attack (AoA) for the configuration is reached, alpha protection (alpha prot) takes over so that the maximum alpha for configuration is held but not exceeded.
This maximum alpha is less than the AoA for the stall. The difference between the protection alpha and the maximum alpha provides a buffer-zone which allows a margin for rapid dynamic entry into a manoeuvre.
The handling of the Airbus in roll and yaw axes is markedly different from the conventional. In this instance, full side-stick to the right was applied and held. The rate of roll is limited to 15í/s, but the computers will provide 15í/s on demand even if windshear, for example, simultaneously provokes a roll in the opposite direction. In the turn, the computers co-ordinate roll and yaw up to a maximum bank-angle of 33¼. The side-stick was then released at about 30¼ angle-of-bank and the aircraft continued to fly the turn hands off (stick-free) as if the pilot had trimmed it in the turn. There was no natural tendency to return to wings-level: ie positive spiral stability. In order to recover wings-level flight a side-stick demand must be applied.
The A319 behaved in this manner in all turns up to a maximum bank angle of 33¼. Next, full side stick deflection was again applied but then held to the right through 33deg. As before, the rate of roll was limited to 15¼/sec but the aircraft continued to roll to the limiting bank-angle of 67¼. Between 33¼ and 67¼ bank, positive spiral stability is restored, so releasing the stick caused the aircraft to roll back from 67¼ to 33¼ of bank.
Both high-speed and low-speed protection were examined. Both were convincing but the low speed case (VLS) was the more interesting. While still flying the aircraft manually, but with auto-throttle switched on, a low speed of 120kt was selected in the clean configuration. The power reduced to decelerate the aircraft towards the selected speed. When 120kt was achieved I moved the side-stick to pitch the nose up. My sidestick input commanded the alpha protection and then, at at point designated alpha-floor, the autothrottle applied power and the legend "ALPHA FLOOR" appeared in the top left corner of the PFD.
Even more convincing was the ground-proximity warning system (GPWS) performance: an abnormally rapid rate of descent was established with the flaps at Flaps 2, undercarriage up and airbrakes out (with the airbrakes out there is discernable light burble). The stabilised rate of descent was 5,000ft/min. A GPWS warning was simulated, at which I pulled the side-stick onto its back-stop, the aircraft rotated to 28¼ nose-up, the "Alpha Floor" legend appeared, the auto-throttle applied full power and the airbrakes retracted automatically.
Two rapid avoidance-type manoevres were then flown. With the flaps at position 3 (22¼ slats/20¼ flaps) and the undercarriage down (a typical visual-circuit configuration), a collision-avoidance was initiated by applying full left and aft side-stick.
The aircraft rolled to 65¼ bank and pitched 17¼ nose-up, producing a 1,600ft/min rate of climb. Then in the same configuration at 130kt, full back-stick was applied wings-level: the nose pitched up to 22¼, "ALPHA FLOOR" appeared, full power was automatically applied, the nose-up pitch increased to 25¼, the speed stabilised at about 100kts and the rate-of-climb was 1,500ft/min.
Next, an engine failure was simulated as full power was applied during a simulated missed-approach with full flap (27¼ slats/35¼ flaps) and undercarriage down. The A319 has no form of rudder-boost (because, Wainwright says, a pilot might fail to recognise an engine failure immediately if corrective rudder was automatically applied), so I deliberately failed to apply rudder but flew the safety speed (V2) in the climb-away. The aircraft turned gently towards the dead engine. I then applied rudder to regain balanced flight, which required a foot-force of about 30kg (60-70lb) and was not automatically trimmed. The rudder-trim knob is on the centre consol.
Wainwright was happy for me to stall the A319, which required him to switch off two computers, thus downgrading the fly-by-wire from its Normal law to Direct law with no alpha protection. Gear and full-flap were selected, the power was idle and the trim-speed 120kt. At 20¼ AoA there was light buffet but roll-control remained good and there was no wing-drop tendency. The stall was benign and not clearly defined by G-break, nose-drop or slice.
The aircraft was then climbed to 39,000ft where turns were flown at 45¼ bank to gain an impression of the handling at buffet-boundaries. At mach 0.74 very slight buffet could be provoked. At mach 0.8, light buffet was noticeable but the aircraft was obviously happy being manouvred at its maximum cleared operating level.
At this point it was clearly possible to answer the questions I posed earlier. I found the A319 very user-friendly and fun to fly. In addition to the exercises already completed, I flew two manual ILS approaches, both by this time at night, and found the aeroplane natural, trustworthy and assuring. I enjoyed the "carefree" protection afforded by the fly-by-wire when the corners of the A319's flight envelope were being explored. I imagine that a young and inexperienced first officer joining an Airbus fleet soon after pilot training would feel at home in an A319. He or she would almost certainly be computer-literate and the A319 is to some extent a large aeroplane with a light aeroplane's control-forces and responses, yet with none of the drama attached to asymmetric flight in some twin-engined trainers.
As far as the experienced Airbus first officer returning to a conventional aeroplane is concerned, he would certainly have to re-accustom himself; but as British Airways' flight training department once responded when asked about such a situation: a pilot may forget everything else, but never his early training. Besides which, the world's airlines are moving into a FBW generation.
Source: Flight International
