Flight Test: Pilatus PC-12NG
- Credit: Archant
The New Generation model builds on the PC-12’s established reputation as the bizjet rival that takes unprepared strips in its stride
Words: Dave Unwin
As the propeller blades slow, feather and stop, I can’t help but be impressed. I’ve done quite a lot of gliding over and around mountains, but never in an aircraft with a MTOW of five tons! As you approach a Pilatus PC-12 the initial impression is that ? for a single-engined aircraft ? it really is a big machine. Standing 4.26 metres tall and with a wingspan of 16.28m, it towers over most other aircraft, even twin-engined ones.
The Swiss have always had a reputation for quality engineering, and as Pilatus production test pilot Jan Schatteman and I walk around the gleaming PC-12NG I can see immediately that it is beautifully made.
Starting at the spinner, it is powered by a Pratt & Whitney PT6A-67P turboprop. This engine can produce up to 1,845shp, but is flat-rated to 1,200shp. All that power is converted into thrust via a four-blade (five-blade for the 2016 version) Hartzell prop, which is both fully feathering and reversible.
As I inspect the wings it occurs to me the single-slotted Fowler flaps cover a large proportion of the trailing edge (67%, to be precise), not leaving much room for the ailerons. The reason for the big flaps is to keep down the stall speed, but as small ailerons often result in reduced control authority, spoilers are often fitted to augment lateral control (as they are on the TBM series).
The PC-12, however, doesn’t have them and I make a mental note to check the roll rate. The wings feature elegant winglets, and I wonder if perhaps these contribute to the aileron efficiency, possibly by constraining span-wise flow.
The Honeywell weather radar is housed in a neat pod at the starboard wing tip, while de-ice protection is provided by Goodrich pneumatic boots on the wings and tailplane, and engine bleed-air to the intake. The windscreen and prop are heated electrically ? a much better method than ducting engine bleed-air onto the screen. Bleed-air windscreen heating systems are always noisy, and less efficient at reduced power (like during the descent and on the approach, just when you need them). Using electricity to heat the windscreen is a far better idea, which is why most airliners use similar systems.
I can see the PC-12, in many respects, has been designed and built to far higher specifications than are required. Many of its features are more reminiscent of a transport category aeroplane, although with a maximum ramp weight of 4,760kg, the FAA doesn’t require a type rating. In Europe, however, the EASA requires as the minimum a PPL with HPA endorsement and type rating training. This is typically one week of ground school and a minimum of ten hours flight training with the emphasis on single-pilot IFR.
The next item to catch my eye is the undercarriage. The PC-12 is approved to operate from unimproved landing strips and one glance at the rugged-looking double trailing link main undercarriage and low-pressure tyres reveals why.
The wheel track is commendably wide (as the main gear retracts inwards into the wings, while the nose leg retracts backwards into the fuselage). While studying the nosewheel I note that, for a tricycle undercarriage, it really does seem to provide a lot of ground clearance for the prop and this is maintained even with a flat tyre and the nose leg compressed ? very impressive.
Moving towards the tail, I note the two ventral strakes and large dorsal fin, but what really gets my attention is the giant cargo door aft of the wing. At 1.32 by 1.35m it is absolutely enormous, and as it opens wide and is hinged at the top, loading and unloading are easy. It is held open by a gas strut and closed electrically.
The aircraft not only has powerful LED landing and taxi lights on each undercarriage leg but there are more lights in neat underwing ‘blisters’. No wonder the aircraft is such a firm favourite with Australia’s Royal Flying Doctor Service, which operates a large fleet of them, as well as other freight companies, air ambulance operators and the military.
The cargo door is complemented by the cabin ‘airstair’ door forward of the wing, immediately aft of the cockpit. Both doors are on the port side. I really like this two-door arrangement. If you’re using the aircraft as a freighter, you can fill the cabin to capacity without having to leave space for an aisle. (Most small freighters ‘bulk out’ ? run out of space ? before they ‘gross out’, or run out of weight-carrying capacity, which is why the Cessna Caravan’s cargo pod is such a popular option). Moreover, I imagine most private owners would prefer to check personally the door has been shut and locked.
The PC-12 features a large T-tail (an unusual configuration in an aircraft of this class) with a ‘bullet’ fairing, and is fitted with a stick shaker and a stick pusher. I ask Jan what the stall is like, and he replies with a grin that I will soon find out for myself!
By now I’m itching to find out how the NG flies. I’m keen to get into the cockpit, but as the big cargo door and large cabin have always been major parts of the PC-12’s success story, I examine them first. The cabin’s length (excluding the cockpit) is an impressive 5.16m, and with a width of 1.52m and a height of 1.45m, it really is spacious. At the back of the cabin is the baggage compartment, which has a capacity of 1.13cu m and is heated, pressurised and fully accessible in flight.
Another excellent feature is the design of the lavatory. This is immediately aft of the cockpit, and is closed off on both sides by folding doors (many aircraft use curtains instead of doors).
In the cockpit I find the seats are comfortable and offer plenty of adjustment (even the armrests move, while the headrests have six positions). The rudder pedals adjust over a good range, while I fully approve of the fact that although the passenger seats have three-point restraint systems, the pilot’s seats have four-point harnesses.
In common with other large single-engined turboprops, such as the Cessna Caravan and TBM-900, one of the PC-12’s biggest selling points is that it is not only certified for single-pilot operation but is very much aimed at the owner-pilot.
Consequently, I’m curious to see how ‘user-friendly’ the cockpit is. Although the PC-12 is big, the cockpit feels as if it is from an even larger machine.
The test aircraft’s instrument panel is fitted with the advanced Honeywell Primus ‘Apex’ suite. This consists of four identically-sized liquid crystal display screens arranged as a PFD in front of each pilot, with the other two (functioning as MFDs, one for systems and the other for situational awareness) mounted vertically in the centre of the panel. Each screen has a diagonal size of 255mm and is easy to read, even in bright sunlight. Cleverly, each screen can be sub-divided into 1/6, 1/3 or 2/3rd sections, with each containing different data, such as engine parameters or navigation information.
Aircraft configuration, such as trim, undercarriage and flap position, is shown here. It’s an elegant and intuitive system, yet although each one of the three individual undercarriage position icons can show seven different displays, I’d still like three lights adjacent to the undercarriage selector. There are no analogue instruments at all, as the back-up instrumentation consists of a small, self-contained emergency standby instrument system to the left of the captain’s PFD. This neat little unit displays attitude, speed and altitude, and can run off its own integral battery in the unlikely event of a total electrical failure. The installation of the Apex system has meant an alpha/numeric keypad for the Flight Management System is located below the lower MFD, with a large cursor control device aft of the power control lever.
Jan demonstrates how to programme the FMS by moving the cursor with the track ball, while inputs are confirmed by using the ‘enter’ softkey, just like any computer. It appears to be both easy and, more importantly, intuitive. As the flight deck is ‘wireless’, it is possible to input data swiftly and simply. This is very useful when programming the FMS with multiple sectors or a particularly complex flight plan.
Instead of a propeller lever, control is automatic and prop speed never exceeds a nice, slow (and quiet) 1,700rpm. Another transport category-type feature fitted to the aircraft is the Crew Alerting System. There are red ‘Master Warning’ and orange ‘Master Caution’ lights, sensibly sited just above the PFDs, while the actual nature of the out-of-limits condition is displayed on the systems MFD.
As on many turbine-powered aircraft, the switches for most of the electrical systems ? such as the external lights, starter and generator ? are mounted in an overhead panel. The centre console carries just a few switches and rheostats for the internal lights, along with the power lever, fuel condition lever and flap selector. As mentioned earlier, there is no prop control, so I turn my attention to the control yoke. This is liberally studded with switches, buttons and even a trigger, which must be pulled to allow use of the trim control.
One aspect of the cockpit I particularly notice is how big and robust the switches (mostly large rockers) are. Yet I think the switches would perhaps be better colour-coded (they’re all a somewhat anonymous grey).
The start sequence is very straightforward ? simply switch on the batteries, press ‘start’, and at 15%Ng move the fuel condition lever to ‘Ground
Idle’. The engine lights promptly and we move onto the pre-takeoff checks. These include checking the stall protection system (remember it has both a stick shaker and a stick pusher) lowering the flaps to 15° and setting the trims.
Taxying from the Pilatus factory to Buochs airport is an unusual and possibly unique experience as you cross a busy road. The traffic lights are (properly) biased in the pilot’s favour and I’ve never had a long wait!
As the nosewheel steers through the rudder pedals and the hydraulic brakes are both powerful and progressive, taxying is easy. Although I ensure the power lever is on the idle stop, in common with most turboprops, there’s so much thrust it wants to taxi faster than I do.
Rather than ride the brakes, I pull the power lever up over the gate and back into the beta range. Approaching the runway, I push the fuel condition lever to ‘Flight Idle’ and carefully taxi into position. Once lined up on Buoch’s 2,000m Runway 07, I bring the power up against the brakes. A glance at the windsock shows a gentle crosswind from port, while as ambient conditions are essentially ISA, we have a density altitude of about 1,500ft. With two POB, no baggage and 750kg of Jet A-1 in the tanks, we are around 1,040kg below the 4,740 maximum takeoff weight, with a fairly forward C of G.
With 1,200hp at my command the acceleration is excellent but unlike most of the other turboprops I’ve flown, you don’t have to monitor the torque gauge in the PC-12, as the torque limiter automatically protects the engine. Instead, I just push the power lever forward to the stop and concentrate on keeping straight.
Tracking the centreline is easy, despite the crosswind. The airspeed increases quickly and I rotate at 85kt. It is note-worthy how little the pitch attitude seems to change at rotation, but this could be an optical illusion, as the long cowling slopes down and away from the cockpit. I then retract the undercarriage, engage the yaw damper and raise the flaps. The undercarriage comes up with no discernible change in pitch trim, but as the flaps retract the trim changes and the aircraft seems to ‘settle’ slightly, although it’s easily trimmed out (as long as you remember to pull the trigger before operating the trimmer).
As you’d imagine, the combination of 1,200shp turning a big four-blade prop produces considerable amounts of precession and P-factor. Consequently, without the yaw damper you have to adjust the rudder trim whenever you change either the airspeed or power setting if you want to keep the pedal forces neutral and the slip ball centred. With the yaw damper engaged, the automatics keep the slip-ball centred, but it’s slightly disconcerting initially to feel the rudder pedals moving under your feet.
I let the aircraft accelerate quickly to 130kt indicated, and as we’re relatively light, the rate of climb is phenomenal. We’re soon at 10,000ft. An examination of the general handling reveals the roll rate to be brisk, and with surprisingly low stick forces. I had read earlier models were rather heavy in roll, but one of the changes Pilatus installed in 2006 was a servo-tab in each aileron. For such a big machine, I find it pleasant to ‘hand fly’. The control harmony is good, while the stick-free stability is outstanding.
Jan encourages me to make full use of the PFD, and I find if I place and hold the flight-path marker icon on the horizon’s ‘zero-pitch’ reference line then I don’t lose a foot of altitude!
We then move on to slow flight. As the PC-12 has a T-tail, it is fitted with both a stickshaker and a stick-pusher. There is an electrically heated A o A vane in the outboard leading edge of each wing, and when this senses the alpha is approaching a critical value the stall warner sounds and the stick-shaker actuates. If no recovery action is taken then the stick-pusher fires.
This pushes the control yoke forward with a force of around 28kg. As we are a good way below MTOW, with the flaps at 40° I manage to get the IAS down to almost 65kt before the shaker activates, while the pusher fires at about 60. These are pretty slow speeds for an aircraft able to cruise at up 270kt TAS and 30,000ft, so with this in mind we climb up to FL300.
The PC-12 is very much a ‘going places’ machine, and not only is it in its element at altitude but sometimes favourable winds can add 100kt to the groundspeed. From our lofty perch, Jan points out Austria, France, Germany and Italy, before we get back to business. The maximum cruise speed is 280kt TAS, but a more representative (and efficient) speed is between 250 and 260.
With an OAT of –44°C, conditions are essentially ISA ? and at 255kt TAS we’re only burning around 225kg/hr. Jan directs me to perform an emergency descent, as if the pressurisation has failed. As with most turboprops, if you pull the power right back the prop generates loads of drag, and it proves easy to achieve a high descent rate (8,500fpm) without excessive speed. As for the pressurisation, all I can say is I don’t even notice it working, which is exactly what you want.
I level out at 12,000ft and Jan takes control. “There’s a way we can burn even less fuel,” he grins, and I nod enthusiastically. In the briefing Jan had explained that during production test flights and engine change-related maintenance flights, company test pilots perform an in-flight shutdown and re-light within the glide-cone of Pilatus’s base airfield.
I can see we’re practically overhead Buochs, so having informed ATC of our intentions, he pulls the fuel condition lever back, the prop disc turns into four blades, which slow and feather ? and we’re in a 3,600kg glider, high above the Alps.
As an experienced sailplane pilot, I automatically note our speed, sink rate and altitude, and then do a quick ‘final glide’ calculation. We’re gliding at 115kt IAS, while sinking at 800fpm (‘eight down’ in glider parlance), meaning we would have thirty minutes from a 30,000 feet cruising altitude to restart the engine. In the unlikely event of it not restarting we could glide around sixty miles, enabling us not only to reach many suitable airports, but even several different countries.
It does restart, of course, and we carry on with the test. Jan is keen for me to see the automatic side of the PC-12, so we head off to Grenchen, a less-than-1,000 metre GA airfield close to Bern, where the autopilot flies a perfect ‘precision approach’, (aka ‘coupled baro-VNAV’) even though the ground-based navaids make this particular runway non-precision (it only has VOR/DME).
As both a production test pilot and instructor, Jan knows the PC-12NG and its systems both inside out and back-to-front.
Returning to Buochs is easy in the outstanding visibility, but in more inclement weather the exceptional situational awareness provided by the Apex system would’ve been much appreciated, particularly as the 7,000ft-tall Mount Pilatus is inside the circuit when you’re downwind for Runway 25.
Jan demonstrates an impressive short-field landing with full reverse and then it’s my turn. The takeoff is easy but with so much power it’s imperative to be in front of the aircraft as circuit altitude is reached quickly.
The undercarriage and flaps both extend smoothly, although the aircraft does balloon slightly as the flaps reach forty degrees. Jan recommends placing the flight path marker symbol on the virtual runway’s threshold (remember the PFD uses synthetic vision) and then controlling the speed with power. This works out pretty well, and after a smooth touch-and-go the second landing is gentle. I’m pleased, but Jan deflates my ego somewhat by pointing out the trailing-link undercarriage is a real flatterer, and you actually have to apply yourself to make a bad landing.
In conclusion, I can now clearly see why the PC-12 is so popular. It’s a real ‘pilot’s aeroplane’, with good performance and fine handling. I cannot think of another single-engined turboprop I’ve flown capable of hauling such a heavy load (or nine passengers) or flying over 1,800nm from a short, unprepared runway.
Comparisons are meaningless ? the PC-12NG is, quite literally, in a class of its own.
You may also like: