A320 under test Immediately the A320 lifts clear of

Toulouse's runway the pilot flicks it like a fighter, pulling up and left into

a steep climbing turn. There is none of the old trick of holding it down to build a speed safety margin; the heart-stopping aspects of the manoeuvre were the obviously low speed and ground proximity as the nose rotates 30° up and the right wingtip swings skyward in a 45° bank. The row of watchers on one of the Airbus flight operations centre's open walkways expel incredulous multilingual blasphemies, then laugh with delight.

Pierre Baud, vice-president flight divi­sion and senior test pilot, is flying the A320, starting the sortie with the kind of take off which Airbus knows will stun the audiences at Paris. Airbus test pilot Gordon Corps, formerly a flier in the Concorde test programme, describes what

Last year the Farnborough display-stopper was Airbus Industrie's test A300 with its simulated fly-by-wire handling. This Paris it is the real thing in the A320. David Learmount reports from Toulouse.

this A320 display take off is like to perform: "The first few times I pulled the stick fully back, but then the world dis­appeared and I chickened out. I wasn't used to losing visual reference like that".

It may look good but it is not going to impress paying passengers. What it is

There are two A320s involved in the flight-test programme already

intended to display more than aircraft attitude is a mental attitude by the test crews—absolute faith in the A320's flight systems to protect them against what would normally be the results of demand­ing too much of the aircraft near the ground. The flight-test programme has logged more than 200hr airborne now, but confidence in the systems to keep the air­craft within a defined, safe flight envelope whatever might happen was built up within the first few hours. Another favour­able reaction was that of one of the French civil aviation authority (DGAC) certifica­tion programme pilots whose precon­ceptions about what a fly-by-wire aero­plane would feel like to fly turned out to be wrong: "I felt I was flying a nice aeroplane, not a computer," was his reaction.

However natural it feels to fly an A320, you are flying a computer, or to be more

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accurate, four computers. The throttle levers also "speak" to computers.

There is a considerable psychological problem among pilots and certificators towards electronic control, says senior vice-president engineering Bernard Ziegler. The test programme is intended as much as anything else to work toward dispelling this automatic mental attitude which believes that, as Ziegler puts it, "hardware is more reliable than the electronic". He is fond of using parables involving animals to explain the concep­tual change: there is his now-famous likening of the advance in the A320's control to the one major advantage that a horse and cart has over the motor car—the horse follows the road automatically while the car has constantly to be steered. Now he explains the advance from mechanical connections to electronic instructions with this simile: "We are moving from the physical to the mind. If we had not gone this way we would still be monkeys". With electronics, he adds, "we know exactly what we are doing. There is no guesswork any more".

The psychological problem Ziegler refers to tends to disappear very quickly among those who become involved with operating the A320, he says. But he confesses to being concerned about a lack of media comprehension.

About 75 per cent of all air transport accidents have pilot error as a significant or originating component, says Ziegler. The A320 is designed to reduce pilot error not just by the doubtfully-effective method of reducing workload, but by actual prevention of the pilot from acci­dentally exiting the flight envelope, and by allowing him to fly the aircraft right to the limits of the aircraft's performance safely when the situation demands it. What about the problem that a pilot once converted to the A320 will take con­siderable conversion back to a tradi­tionally controlled aircraft? "Do we have to refrain from advance because of a difference in handling and problems with conversion back to the old system?" asks Ziegler. And he points out that the new Airbuses, the A340 and A330, will be fly-by-wire. Boeing plans it for its 7J7.

At the end of this month the A320 will have production standard Snecma/ General Electric CFM56-5 engines fitted to it and the programme from there onward will be in a position to guarantee engine performance. Two engines have been shipped back to Cincinnati to have the batch of improvements installed which brings them up to production stan­dard. These include installation of a reshaped fan stator which improves flow stability; turbine modifications; and the light alloy engine cowling which was tending to distort slightly in flight is being replaced with the production carbonfibre one.

There are two aircraft involved now in the A320 test programme. The first aero­plane had made the type's maiden flight on February 22, and the second joined it on April 27. Airbus had positively lunged into the programme, hitting height and speed maxima during the maiden flight on a day where instrument meteorological

Right Test pilots are pleased with the A320's handling characteristics. They say "it is not like a computer to fly". Below On the approach at Toulouse. Below right The flight-deck is all-digital, with sidestick controls

conditions prevailed between 300 and 12,000ft (Flight, March 7, page 26). Test­ing is some 20 per cent ahead of schedule.

It is probably self-evident that a great deal of the A320 is basically the same as any other airliner and therefore has to undergo the same testing; but the part of the programme which is exercising every­one's minds to the limit is definition and final adjustment of the flight control laws, which ultimately means the software which determines how the aeroplane reacts to the pilots' sidestick inputs via the flight management system (FMS) com­puters to the controls.

Various control modes can be selected during flight, which determine just how much protection the pilot has against flight envelope exit conditions like stall and overspeed. When Normal is selected full protection applies. There is no ques­tioning of normal mode flight control laws as they apply during almost all of any flight. An example of an area where there is still discussion about finalisation of software is the landing phase.

Normal mode, when the aircraft is well clear of the ground, means that the A320 responds to sidestick input according to a programmed manoeuvre demand law. In pitch it delivers a flightpath, not merely a rotation about an axis. Sidestick pitch

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deflection is proportional to g demand, with pitch rate feedback giving stabilisation. In normal mode, roll rate is proportional to manual deflection of the sidestick, but is limited to 15 "/see. Yaw normal gives auto­matic yaw damping, turn co-ordination, and rudder application limitation, even though the rudder link is mechanical, not fly-by-wire, but is linked with the flight management guidance computer (FMGC). All of this software is defined but for possible minor adjustments.

Problems emerge in deciding what the pilot wants to feel during the last part of the final approach and during the landing flare. Remember that the sidestick has no artificial feel, it is simply spring-loaded central. Letting the stick go so that it takes up its neutral position does, during flight, deliver a straight-line flight path whatever you subsequently do with the speed or the throttles (until the aircraft approaches either the stall or maximum operating speed, when appropriate atti­tude changes automatically start to be applied for protection), because stick neutral means no demand for g.

Imagine the pilot is using the sidestick under normal mode as he starts the land­ing flare; as soon as he had brought the attitude and the rate of descent to what he wanted he would have to begin to reduce

FLIGHT INTERNATIONAL, 13 June 1987

stick pitch deflection, or even let it spring central to its neutral position. This is the exact opposite to what a pilot is accus­tomed to and feels comfortable with. It would be the equivalent of operating a normal aircraft with an automatic pitch trim follow-up system—which has not been found to be popular.

Airbus wants pilots to feel happy with what the aeroplane feels like at all phases of flight. They are already content with its feel and handling during all other phases of flight; now it is necessary to keep them happy during the last couple of hundred feet without having to flick any switches to change the systems from normal to some kind of landing mode where different control laws would provide the feel they are used to.

Gordon Corps says that Airbus has been testing an automatic switch-over to a direct stick-control surface law, switch­over occurring at some arbitrary height like 100ft. That would give the intended "feel" at flare, with a need for continual pull-back during the flare and while lowering the nosewheel. The problem is that a control-law change late on finals is not a nice concept, and in losing normal mode the stability that goes with it goes too.

What Airbus wants to arrange is some-FLIGHT INTERNATIONAL, 13 June 1987

thing which is either a continuation of the normal cruise laws, or which is in practice so like them that a law change will not have any momentary "feel" change, which will continue to give all the flight envelope protection which normal gives, but in the end feels natural and firm at the flare. What the manufacturer is testing cur­rently is a law where stick displacement is proportional to attitude (theta), because that is what a pilot is selecting (in addition to IAS) at the flare. Also being looked at is software making stick displacement give a theta change by demanding an alpha (angle of attack) change, which produces the flight path change the pilot wants. All these software ideas are being developed in the aeroplane, not in the simulator because, as Corps puts it, "You can't frighten a pilot in a simulator", so the results would not be valid.

Flutter tests are nearly complete, and most of the work now under way concerns what Corps calls "mundanities" like systems development and warning

systems work. A320 stall protection comes in at an

alpha of 17°. What happened with stall protection disarmed? Corps did not really want to answer that question on the grounds of its irrelevance. The possibility of stall protection failure will be one in 107, he pointed out. Tell us just the same, Flight suggested.

Stall in the A320, Corps says, "does not have any strong stall identification char­acteristics. It just sits there and buffets. Releasing the stick brings the aircraft straight out". Using direct control mode the authorities have taken the A320 well into the 25°-30° alpha area of the stall, and they have been satisfied.

Leaving aside the short finals and flare area where control laws are still under definition, pilots are describing the A320's behaviour in the air as "sweet as an angel". Now the test team is settling into the systems work which Corps describes as "producing no surprises at all. A bit of a grind". 83

Aerospatiale's A320 final assembly line plans to produce eight aircraft a month by late 1990

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