Impressions – A320 Glass Cockpit

Having suffered artificial horizons with the pointer at the bottom, directional gyros which do not rotate in a natural sense, three handed altimeters which were possible to misread by 10,000′, and finally an early form of strip instrument in a Hunter Trainer, I have developed a somewhat jaundiced eye for so called “improvements” in instrument presentation. It was with that personal background to instrument flight that I approached my ride in the A320 simulator.

After a pleasant flight down to Tullamarine, courtesy of Ansett, I presented myself to Captain Fred Boomsa the Ansett A320 Fleet Manager – Flight Operations. I had been generously allocated an hour for briefing and flight in the simulator which was certainly enough time in which to form an impression which was my aim. By no means would I be presumptuous enough to attempt an appraisal.

My immediate impression on being strapped into the left hand seat was of an uncluttered, clear instrument panel with just two relatively large instruments directly in front of me. They are 184mm square multi colour displays and together make up the ElectronicFlight Instrumentation System (EFIS). There arejust 12 instruments in the A320 panel and the difference compared to earlier aircraft is readily apparent from the photographs accompanying this article.

Of course the most striking difference in the cockpit layout is the lack of a conventional control column. The A320 is the first commercial aircraft to have fly by wire (FBW) controls and is controlled by a side stick controller (SSC). A convenient arm rest located under the forearm can be raised to provide a comfortable grip on the short “stick”.

Captain Boomsa had previously explained that the main instrument in front of me, the Primary Flight Display (PFD) essentially replaced seven instruments. Clearly the main display was the artificial horizon space, with airspeed and mach number,(the latter coming up above Mach . 5 as a digital reading), shown on a strip to the left. V1 and V2 are displayed, having been programmed in for the specific flight conditions. The system has the ability to show the minimum selectable speed, VLS, plus alpha stall speed protection which comes up on a black and amber scale and the stall speed itself on a red scale. F speed which is the minimum speed to take up flap is shown, as is S speed the mini mum speed to retract the slats. A green dot shows the minimum manoeuvre speed and there is an overspeed scale. Finally, the maximumspeed for flap selection is shown when reducing speed for the approach. A trend arrow pointing up shows airspeed increasing or pointing down decreasing, with the length of the tail an indication of the rate. The actual airspeed reading is indicated by an amber triangle in the centre of the strip. Height is displayed on a similar strip to the ASI, on the right of the PFD. The height selected is shown at the top if above the present altitude and below if below present altitude. A blue box around the height turns amber when the height corresponds with the selected height. Outboard of the height scale is the VS!, again in the form of a strip but with the strip pointer sloping up or down as an additional aid to indicate the direction.

Heading information is displayed in strip form at the bottom of the instrument, the lubber line is yellow and the track made good is indicated by a green lozenge. At the top of the AH is a sky pointer which has a slip index incorporated in its bottom half. In the event of an engine failure, the bottom half turns blue and becomes a beta target. Additional information displayed includes the radio altimeter when below 2,500 feet, the outer and middle markers, and glide slope indications are shown through a selectable display. QNH is displayed below the altitude scale and if above the transition level, standard is shown.

The Flight Director consists of a horizontal bar for pitch guidance and a vertical bar for turn guidance. A small black box represents the aircraft and is centred over the two bars to obey the command of the flight director. I had previously flown an early series BAe 125 fitted with a flight director in which the presentation consisted of shallow inverted ”V”s, one being the aircraft and the other the flight director command. The aircraft was flown to superimpose the aircraft “V” over the Flight Director “V”.

A navigation display of equal size to the PFD is situated to the right of the latter (in the left hand seat). This can be changed from a round display to an arc display and the scales can be expanded as required. It displays ground speed and true airspeed readouts, plus true wind direction and speed, including an arrow for orientation. The departure and destination airports can also be entered plus the appropriate Standard Instrument Departure (SID) and arrival plates. A group of standby instruments is to the left of the navigation display and finally the engine instruments are mounted in the centre console.

All systems controls and switches are mounted in the overhead panel and function on the “dark cockpit” principle, that is if they are selected on there is no display. They are automatically monitored and if a system goes outside the normal range, a warning light flashes green turning to amber and the appropriate procedure is displayed.

Captain Boomsa then went on to explain the “Laws” controlling the flight control system computers. Normal Law provides protections plus assistance to the pilot. The aircraft will do what is commanded of it provided it remains within the normal envelope. The system will only modify pilot input if an attempt is made to go outside the envelope, ie overspeed, overbank, overstress etc. The control demands are progressively modified to preserve safe flight as the envelope boundaries are approached. Should the commands go outside the boundaries they are inhibited. With the wings level in Normal Law, the system operates on a 1g flight path. This means that the aircraft can be taken from 130 knots gear and flap down, up to 350 knots hands and feet off and the aircraft will maintain constant height. If the wings are not level, the system changes to a Zero Pitch Law, where provided the bank angle is less than 33 degrees, it will hold the pitch attitude you have selected for level flight.

The next step down is Alternate Law in which there are half the protections plus auto trim, the aircraft being slightly more sensitive than in Normal Law with the roll rate 30 degrees per second as opposed to 15 degrees in normal law.

Direct Lawis the same as a conventional control system in that there is a direct stick to control surface relationship. There are no protections and trim is controlled manually; in effect it is the same as any other aircraft.

Indications are provided on the PFD as to which Law the flight director is functioning in. Normal Law is indicted by green “equal” signs either side of the AH, with Alternate Lawindicted by crosses.

Finally, the throttles have an auto throttle function which provides the correct power for the flight profile being flown, without pilot input.

Returning to our trip, after start up, on looking outside I found that we were positioned at the holding point for runway 27 at Tullamarine, at night, in clear conditions. I had experienced visual simulation briefly before in its early days, but found the A320 set up to be totally realistic.

I managed to line up OK using nose wheel steering and then we were on our way. Captain Boomsa coached me in what to do which was simply to fly the small square to the horizontal and vertical bars. Knowing that the flight control system would take care of the flight profile providing I obeyed the commands of the flight director, I must admit that my instrument scan was limited to the centre of the PFD . I had previously flown a side. stick control in the Huey Cobra and had immediately appreciated its worth. I found however that the break out force to overcome the springs in the A320 was greater than I had expected and I found myself over controlling in roll. The answer as always was to relax on the control and let the aircraft fly itself. I didn’t experience the same problem in pitch.

One thing was immediately apparent and that was the lack of need to trim as the system did it for you. That in itself was a quantum leap!

As I settled down my scan began to widen to take in the ASI and thealtimeter. I must confess that I never really became comfortable with the ASI as there was so much information to take in. A longer session of ground school would have helped me to know what to expect. The altimeter was fine as was the VSI. I particularly appreciated the pointer on the VSI, I found it very easy to read. Heading information at the bottom of the PFD read naturally and didn’t present any problems.

Shortly after takeoff we carried out a wide turn and Captain Boomsa then set us up for an ILS (Instrument Landing System) approach. My glide slope was a little sloppy but we arrived near enough to a point where a landing could have been made. The auto throttle did all the work, pegging the approach speed all the way down. We then executed a missed approach where again the system did all the work with me just trying to keep the little square centred as the pitch bar commanded up.

Next was a most convincing demonstration of the inherent safety built into the flight management system. I was told to apply full back stick whereupon the system took over, limiting the actual control surface deflection and applying climbing power. We proceeded to climb in a controlled fashion with no hint of a stall.

As time was running out it was back to Tullamarine via another ILS and a full stop landing. Time hadn’t permitted a full brief on the throttles so my mentor had to apply reverse thrust after I finally got it down from an over flare. Heavy braking was necessary to prevent us running off the end but we stopped in time. I then blotted my copybook by taxying us onto the grass through over controlling on the nose wheel steering! Fortunately no flashing lights or crashing sounds resulted so I concluded that either the A320 has a low footprint or the ground was solid! My conclusions? The flight instrument set up in the A320 truly represents a quantum leap in flight information presentation. It is easy to read, precise and non-confusing and really provides that essential picture I mentioned at the beginning. I felt that with a little more time I could have been flying the aircraft with a fair degree of accuracy. Unquestionably, the use of colour in the dis- play is a major factor in enhancing information presentation and ease of interpretation. Its the difference between monochrome and colour presentation in a video monitor.

Evidently younger pilots take to it more readily than the older hands which is to be expected they don’t have to be deprogrammed. I think it would be safe to say that what we see in the A320 now, will be the industry norm by the turn of the century. My thanks to Ansett and Captain Fred Boomsa.