When Aero International (Regional) (AI(R)) was formed in January 1996 from the regional-aircraft businesses of Aerospatiale of France, Alenia of Italy and British Aerospace, its declared policy was to manufacture and market a family of complementary regional aircraft. That family now includes the Jetstream 41 turboprop (with 29-30 seats), the ATR 42 and 72 turboprops (48 and 66 seats), and the two RJ four-engined jet airliners (the RJ85, with 85-92 seats, and the RJ100, with 100-110 seats).
The company is keen to review, revise and update its aircraft, and has recently completed a demanding programme to update the ATR 42 and 72. The aim has been to refine both types by incorporating the latest relevant technology, and to increase the commonality between the two. Both models, from inception, had the same type of wing, tail and fuselage - the 72 having a stretched version of the smaller aircraft's fuselage. Now they share the same engine types and propellers, and commonality is such that pilot type ratings are good for both aircraft, and airline-engineering organisations face far fewer headaches over spares holdings and maintenance procedures. The newest simulators are even designated "ATR 42/72" and need only an easily accomplished change of instrument panel to represent either version.
Both aircraft types have sold well since the 42 was launched in October 1981 - over 500 units to date - although success has not been without its pitfalls. In 1994, an ATR 72 crashed near Roselawn, Indiana, with the loss of all on board. The accident happened in extreme icing conditions with several exacerbating circumstances. The accident, together with another to a Jetstream, nevertheless led to damaged public confidence in turboprop airline safety in the USA - and imposed upon Aerospatiale an onerous responsibility to ensure that the ATR series was more tolerant to icing conditions.
While modifications were being undertaken to counter the airframe-icing problem, work was completed by AI(R) to enhance the general appeal of the 42 and 72. The latest versions, the 42-500 and the 72-210A, have the same Pratt & Whitney 127F engine and the same Hamilton Standard HS568F six-bladed propeller. The electrically synchrophased propeller blades are part of the package which AI(R) is incorporating in the 72-210A to make the aircraft quieter, smoother and cheaper to operate.
Dealing with the ice
The aftermath of the Roselawn accident revealed that ice could build up on the upper-wing surface behind the leading-edge de-icing boots (but only with supercooled rain drops spreading back over the aerofoil before freezing) and interfere with roll control by disrupting the air flow over the ailerons. Wider-chord de-icing boots have been introduced to break up any ice forming behind the leading edge, and spring tab assistance of the ailerons has been incorporated to improve their effectiveness in icing conditions - although the mechanical control runs to the ailerons remain as before. Because of the high-wing configuration of the ATR, it is not possible to see wing-icing from the cockpit but, as a result of the tests AI(R) has done by flying behind a "water bomber" in icing conditions, guidance to pilots on how to identify hazardous conditions from the cockpit has now been provided.
In addition to the "commonality" now offered to operators of mixed ATR fleets, AI(R) has aimed to reduce noise and vibration levels in the cabin by cutting noise and vibration at source through the slower rotating, better synchrophased six-bladed propellers, and by ameliorating noise and vibration through frame damping in the fuselage structure and skin damping to the centre portion of the fuselage.
Flight International was able to sample the effectiveness of these modifications during a flight test from AI(R)'s plant in Toulouse, France. The aircraft used was a production 72-210A. It conforms to the classic mould of high-wing turboprops, with its fuselage sitting comfortably close to the ground on a relatively narrow-track (4.1m) undercarriage, each of the double-wheeled main legs folding neatly into a pontoon on either side of the lower fuselage; the main and nose-wheel doors remain open while the wheels are extended.
The high wing ensures that the engines are kept above the worst of airport debris and water spray from contaminated runways, and the 3.8m-diameter propellers are afforded ample ground clearance. The tail-plane is mounted nearly, but not quite, on top of the slightly swept fin. The primary flying controls are all mechanically operated and each has a horn balance. Roll control is provided by the ailerons working in synchronisation with an hydraulically powered spoiler on each wing. The trailing-edge flaps have two segments on each wing and are electrically controlled and hydraulically operated; asymmetric extension protection is provided.
The standard aircraft offered by AI(R) has a passenger door with integral folding steps, aft on the left hand side of the fuselage and a forward cargo door on the left-hand side. There is baggage or freight stowage space in the front portion of the cabin and next to the lavatory in the area behind the passenger door. The 2.6m cabin is designed for flexibility in its configuration, but a typical layout is 66 seats, four abreast, at 787mm-pitch, with a small galley, a lavatory and baggage compartments.
The cross-section is constant throughout the cabin; headroom between the overhead bins is 1.8m and the central aisle is 457mm wide. Suppression of the so called "parasitic" noises within the cabin has been achieved through improved outflow valves, acoustic muffles around the air-conditioning fans and around the hydraulic pumps in the landing-gear bay.
The cockpit
Getting into and out of the well-laid-out cockpit is easy. Each pilot's seat is adjustable fore and aft, up, down and sideways. Once seated, the pilot can move the seat from its outboard position (which allows space between it and the centre console) to align his or her eyes with the "three-ball" indicator on the windscreen central pillar; the seats have reclining backs, adjustable arm rests and four-point harnesses.
There is good stowage space for flight bags outboard of each seat and stowage for slim documents on the side walls of the centre console. The rudder pedals are adjustable for reach using a small crank handle at the lower edge of the instrument panel, and the fairing between the pedals is calibrated with bold lines to help pilots to move the pedals to the setting which suits them best.
The field of view is good: each pilot can see the wing tip on his side of the aircraft, but only by craning his head close to the side window. There are tinted curtains which can be pulled up from the bottoms of the side windows to reduce glare, and an articulated smoked plastic glare shield mounted above each windscreen. None of the cockpit windows opens, so there is an ingenious fuselage hatch by the captain's elbow which enables documents to be passed in and out of the cockpit; escape on the ground for the crew is provided by a roof hatch.
Normal checklists are commendably brief and helped by the "dark cockpit" philosophy - that is, when a system has been selected for operation using the push-button-selection-indicators (PBSIs), all legends are extinguished until the status of the system is changed by the pilots, or a fault occurs. There is a small central warning panel on the captain's side of the centre instrument panel; the integrity of the legends on this warning panel and the push button indicators is checked by a press-to-test switch before starting the engines.
Starting the engines is straightforward compared with that of many earlier turboprops. The right-hand engine is used as an auxiliary power unit (APU) on the ground, supplying bleed air and DC electrics with a propeller brake applied to lock the PW127's free turbines. Upon unlocking and unfeathering the propeller, the right-hand power unit is ready to use. Starting either engine is simply a matter of selecting "start" on a rotary selector switch on the overhead panel and pressing the adjacent start button. Once the engine is rotating, fuel is introduced using the engine condition lever, which has only four positions - fuel off, feather, auto and a mechanical override to be used if the electronics fail. Once selected to auto after starting, these levers need not be moved again until shutdown.
The ATR 72 is usually fitted with one nose-wheel steering control, on the captain's side, but a second for the first officer can be specified. Taxiing is undemanding. The twin nosewheels are positively controlled by the tiller; the steering is quite high geared and takes little practice to avoid over-controlling. The speed is regulated with the power-levers, in the beta range, so that a little reverse pitch can be applied to slow the aircraft or bring it to a halt. Under these circumstances, the propellers are inevitably somewhat noisy and can be clearly heard changing pitch from the cockpit - and presumably also from outside, in the aircraft's vicinity. The wheel brakes are smooth and powerful. The parking brake is operated by a lever on the captain's side of the console; rocking the handle outboard and moving the lever forward releases the brakes, rocking it inboard latches them on when the lever is pulled back.
The all-up weight for take-off was 16,250kg (maximum all-up weight is 22,000kg) and the fuel weighed 3,000kg. The cabin was fitted with seats, but there was no ballast, and with a crew of three, including a flight-test engineer, the resultant centre of gravity (CG) was fairly forward. Company test pilot Bernard Dorance was in charge from the right-hand seat, while the flight-test engineer was at hand on the jump seat to advise on such matters as instantaneous all-up weight, stall speeds and V2 climb speeds, and to record the results of each test point.
The ATR accelerated rapidly on take-off once the power levers had been moved quickly (but progressively) to the "Alternate Power" detent, about four-fifths of the way forward in the quadrant. "Alternate Power" (using 90% torque) is normally used for take-off in the interests of preserving engine life, but 100% torque can be selected if required by pushing the levers fully forward. The rudder became effective at about 30kt (55km/h), but one's left hand remains on the tiller, in case of an abort, until 70kt, when it is transferred to the control yoke.
The airport elevation at Toulouse is about 500ft (150m), but runway 33 left was of sufficient length for an equal V1, and VR speed of 106kt to be used; V2 was 112kt. The aircraft rotated pleasantly and the climb attitude was readily achieved. Retraction of the gear and flaps produced no noticeable pitch change.
In flight
Once the aircraft was clear and settled into the climb, the power-management (PWR MGT) selector switch which had been set at "take-off" was merely rotated to "climb". This produced a small decrease in torque and no fuss from the propellers. For en route operation, the rotating switch would again be moved to "cruise" when the aircraft reached the top of the climb and again to "take-off" for the approach - to permit a roller landing or go-around if needed.
This PWR MGT switch panel is just to the captain's side of the engine instrument panel and easily reached by either pilot. The power levers would only be used for power reduction in the descent and approach. All changes to the PWR MGT switch, and symmetrical use of both power levers, produced the changes demanded smoothly and quietly, the propellers remaining synchrophased throughout.
During the climb, an arbitrary "snap shot" look at stability showed the ATR-72-210A to be positively stable in all axes. The aircraft is normally flown with the yaw damper selected, but de-selecting it, although making the aircraft directionally a little less taut, was largely a non-event. Yaw remained well damped and Dutch roll could not readily be induced. The aircraft may be dispatched without the yaw damper being serviceable.
Roll control, via ailerons and spoilers, was very pleasant for a turboprop of this size with manual ailerons. The control forces and the roll acceleration, subjectively measured, were also surprisingly constant between the high- and low-speed regimes. Rapid reversals could produce slightly disconcerting protests from the wings as they flexed, however.
Throughout the manoeuvring, the electronic propeller synchrophasing worked splendidly, and there was none of the irritating "hunting" of the propellers which can be encountered with electro-hydraulic systems as they struggle to keep pace with flight conditions. Also, the automatic pressurisation was a pleasure both after take-off when the bleeds opened automatically and during the various in-flight sequences. The operation was quiet and surge-free throughout.
Stalls were tackled next. As might be expected with a high tail-plane, a stick-pusher is fitted. The results of the three power-off stalls are recorded in the table. During the approach to the stall, the aircraft was pleasant to fly and roll control remained effective all the way to the point when the stick pusher took over.
Following the stalls, altitude was reduced so that we could simulate an engine failure at V2 in the after take-off configuration of Alternate Power, 15 degree flap and gear up. If an engine failed in anger under these conditions, the falling torque would be detected, the propeller of the failed engine would automatically be feathered and the live engine's power automatically increased to 100% torque. It was not possible to create these conditions in a production aircraft (although the test had been completed ad nauseum with test equipment during the development and certification flying of the 210A). Instead, Dorance waited patiently for me to achieve the V2 speed of 112kt at 4,000ft with alternate power on both engines and then throttled back the left (critical) engine to 12% torque to simulate a feathered propeller and simultaneously manually increased the torque on the right engine to 100%. The event was comfortably contained with a little right bank and about half right rudder deflection held with modest foot force.
At about 6,000ft, the left engine was shut down and the propeller feathered so that the aircraft could be flown asymmetric at about 130kt to look at its handling qualities under conditions similar to those a pilot would encounter when faced with a single-engined approach and landing. Under the prevailing conditions of light weight and lovely weather, it was easy to fly.
Throughout the flight, the ATR was easy to trim. Trimming in all three axes is electrically controlled via two-pole, split switches, one for pitch on each pilot's outer horn of the control wheel, and the two for roll control and rudder on the top of the centre console between the pilot's seats. I liked the rate of trim change in pitch and roll and readily became used to trimming the rudder which always seemed to need a brief pause before the demand became effective. This, Dorance explained, was because the yaw damper took a second or so to recognise the demand and react to it.
INSTRUMENTS
Similarly, in all phases of flight, the instrumentation was easy to control, read and interpret. The flight director is by Honeywell, and provides each pilot with a CRT primary flight display and a CRT horizontal situation display. These are complemented by standard analogue instruments - airspeed indicator, altimeter, vertical speed indicator and radio magnetic indicator. The engine instruments have combined analogue-digital calibrations and are grouped in two columns at the centre of the instrument panel, each engine having seven parameters indicated: torque, propeller speed, inter-stage turbine temperature, high- and low-pressure turbine RPM and fuel flow, oil pressure and temperature. Systems control is assigned to the roof panel where each major system - electrical, hydraulic and fuel, for example - is represented by a clear schematic diagram with control via PBSIs. The exceptions are the lights (external, cabin signs and so-on) and the windscreen wipers, which have conventional switches and rotary switches, respectively.
The aircraft has one autopilot, by AlliedSignal Bendix/King. Its controller is under the glare shield and atop the engine instrument panel; it can easily be reached by either pilot. Above the controller is a small cathode ray tube which displays the mode(s) selected. The two navigation controllers are conveniently placed either side of it. A coupled autopilot approach using the instrument-landing system (ILS) on runway 33 left at Toulouse was ßown; the locator and glideslope were, in turn, captured smoothly and accurately maintained. Speed (100kt in this case) was easily maintained on the glide slope by use of power. At 100ft above the ground a go-around was flown by pressing the power-lever buttons, to disengage the autopilot and set the attitude-director indicator demand bars for the climb. Alternate power was selected by moving the power levers forward, but only after I had inadvertently over-shot the detent towards maximum torque; the detent is doubtless easily found when one has become accustomed to it, but it is sufficiently "soft" to be overridden easily at first.
The ATR was finally flown manually for another ILS approach and two visual circuits with touch-and-goes before the full-stop landing. Basically the aircraft was enjoyable to fly in the instrument pattern and visual circuit because of its well harmonised and pleasant control forces, and the ease of control for the engine and propellers afforded by their electronic, automatic, regulation - and in this instance because it was a peach of a day with excellent visibility, light winds and no weather. The limiting speed for the selection and use of approach flap (15í) is 185kt, however.
This speed is admirable in that it allows higher than necessary marshalling and approach speeds to be flown if required by air-traffic control - but selecting 15 degrees at 180kt (or retracting it) does cause a significant pitch-trim change. I realise that pilots flying the aircraft every day will become so used to this characteristic that they will almost sub-consciously retrim as required. To the newcomer, however, it is a disappointment, particularly as the other handling characteristics are so pleasant for this class of aircraft. I asked Dorance whether automatic trim compensation had been considered, at least for the 15í case, during the planning of the changes to improve the ATR 72. It had not, which presumably means that my criticism has not been often voiced in the past.
I deliberately maintained higher speeds in the pattern and on the glide slope for the manual ILS - at 150kt and 130kt, respectively. The gear limit for lowering is 170kt, and for retracting it is 160kt; the landing flaps can be lowered 30 degrees at 150kt. These configuration changes cause no significant pitch change with the undercarriage alone, and little with 30í flap. The aircraft handles nicely at the higher approach speeds.
Flap selection is through a conventional lever on the first officer's side of the centre console. The undercarriage is selected, normally by the first officer (but easily by the captain if required), using a lever on the right-hand side of the centre instrument panel. Three gear position indicators are above the lever.
The ATR 72 210A is pleasant to land. The main gear is reasonably compliant and, once the nose gear is on the runway, reverse pitch is easy to select and provides good retardation - but at the cost of some associated propeller noise; the wheel brakes are powerful.
Conclusion
I very much enjoyed flying this turboprop. It has been astutely improved to emerge in its present form as a competent aircraft with pleasant handling characteristics, ease of power "management" and control, and noise and vibration at low levels which are unlikely to be bettered in a current-generation turboprop. The open and relaxed attitude of Dorance, both in letting me get on and fly the ATR and in answering my questions, was much appreciated.
AI(R) appears to be a confident organisation which appreciates the imperative need to re-invest in its proven products to embrace the latest technology and maintain vital passenger appeal. Nick Godwin, vice-president marketing, acknowledges the appeal of jet engines, but stresses that airlines cannot ignore the compelling economics of turboprops - whose air-kilometre costs could be 15% lower than for a jet-powered aircraft - provided that they are used on high-density, high-frequency and relatively short-haul (up to about 565km) sectors where they can give flexibility and make money. Godwin and his colleagues are clearly confident in the continuing success of the ATR. From my brief acquaintance with the ATR 72-210A, I suspect that confidence is well placed.
Source: Flight International
