Pilatus PC-21

The next advanced flying training platform that the ADF procures will undoubtedly be staffed in the future by instructors who are currently in primary school – many of their future students are not yet born. Such is the nature of recent generations that manufacturers of some electronic gadgets do not even bother with instruction manuals. The kids of today take little time to figure a device out and then take it beyond the intent of the designer. This is the environment in which this old school military flying instructor finds himself; the challenge of teaching these young people to fly is fascinating. I empathise with the ADF in trying to decide what the next evolutions in military flying training will be. It is difficult to future-proof when buying a long-term training system. The good thing is that the student of today and the future is conditioned for sophistication.

The buzz at Avalon this year was that Project 5428 was back on the front burner after years in the wilderness. This brings back into focus the options available to a stressed ADF in an environment of ‘project paranoia’. Clearly this relatively small budget project has far reaching implications for all aspects of military aviation. It also led to an invitation for me to test fly the Pilatus PC-21. I have flown the T-6 Texan II and would now fly the PC-21 – arguably these are the two serious contenders to become the 5428 ‘advanced’ platform. As an owner of a flying school myself, and former RAAF Qualified Flying Instructor, I can appreciate many of the factors that will decide this competition.

I have had occasion to visit the Pilatus factory several times since I picked up RAAF PC-9/A A23-001with my C-130H in the late eighties. At that time Pilatus had a distinguished history of producing military flying trainers and utility aircraft from a scenic valley in the Swiss Alps. I later became a flying instructor on the PC-9/A and was surprised to find little in the way of training aids and synthetic devices to support the Instructor. I suspect that this may have been mostly to do with the RAAF trying to spend all of the available money on the platform. Certainly the global military training culture at the time seemed to be that support material could be created in-house and simulators were too expensive.

However the flight training world was changing and customers were soon expecting complete integrated ‘training systems’ rather than just training platforms. Interestingly, on that first visit during a tour of the factory my crew and I were shown a mock-up of what would become the PC-12. At the time many considered this to be a risky project as single engine IFR charter did not exist. History has shown that the PC-12 has changed air law and created a new space on the successful aircraft design landscape. It has perhaps also carried Pilatus into the new era of ‘training system’ philosophy to compliment their solid platforms.

Training System

A modern training system includes the ground school product (usually computer based training), synthetic device (the simulator) and platform (the aircraft). It should also include some mission planning and debriefing capability and increasingly an ability to introduce some role specific modules such as weapons system emulation.

The PC-21 computer based training (CBT) product is created by a large and dedicated team based in the factory headquarters building. This team includes former military instructors, computer graphics designers and education experts. The product is extremely interactive and the graphics are exceptional. All the usual feedback, supervision and revision functions are possible.

Certainly CBT has come a long way since my last airliner conversion however the students of today have very high expectations. I was particularly interested in the template software that the team developed internally. This enables the team to convert required content into a CBT module with interactive graphics in a relatively small amount of time. Amendments or additional CBT products can be produced in a timely manner.

The PC-21 simulator is a standard fixed base dome arrangement with control station separate and behind the cockpit. The fidelity is excellent and I’m told uses the same flight model that was developed for the test program engineering sim. Customer simulators are built to individual requirements by a consortium Pilatus has entered into with EADS and AMST. Both EADS and AMST bring considerable experience of high end simulation.

The dome is subject to customer requirements however the sim that I was flying has a BARCO SEER 5 dome. The graphics are extremely realistic and certainly adequate for general flying. The larger SEER 8 dome is recommended for those customers wanting exceptional graphics for intercept training. Certainly the SEER 5 is realistic enough for me to enjoy some superb simulated alpine valley flying – not something we get to do in flat dry Western Australia. I was now well prepared for our flight.

The Aircraft

Of course the key component in the equation is still the aircraft. The decision for Pilatus was similar to what I call the ‘Airbus dilemma’. In deciding a design philosophy the fledgling European Airbus consortium could try to out-Boeing their major competitor or optimise other features to attract buyers. Basically, innovate or die.

For Pilatus the question was do they evolve the PC9 or do they start with a clean sheet of paper to develop a new core design concept. Had Pilatus elected to just evolve the PC-9 it is likely that we would be comparing two essentially identical aircraft because the T-6 Texan II has already followed this road. To ensure a point of difference, and perhaps create a new class of military trainer, Pilatus gambled in a way reminiscent of the PC-12 project.

The challenge for Pilatus was to produce a turbo-prop capable of servicing a greater segment of the training spectrum, while retaining the positive economic and life-cycle attributes of a turbo-prop, and the flexibility to adapt to the changing requirements of the customer. To my mind, the gamble has paid off. This turbo-prop trainer can occupy the space currently serviced by the PC-7 and PC-9 and also challenges the boundary between advanced trainer and LIF. Learning how to operate a sophisticated cockpit takes longer than learning how to go faster. It is logical to put that cockpit into a less expensive platform.

Perhaps the first thing that strikes you when you meet the PC-21 on the ramp is that Pilatus has actually managed to make a sexy looking propeller trainer. This luxury is normally the territory of jet trainers (British designs notwithstanding) and is the first of many ‘jet-like’ characteristics.

The PC-21 owes its sports car looks to the moderately swept high-speed profile wing. Had Pilatus continued with the chunky straight wing used successfully on the PC-7 and PC-9 variants (including the T-6 Texan II) this would have capped the top end performance and roll rate.

At 9.1 metres the wingspan is 1.1 metres shorter than the PC-9 wing. The fowler flaps are big enough to allow a suitable stall speed when configured of 81 knots. The consequently smaller ailerons are hydraulically boosted and are supported by spoilers which begin to deploy at greater than 5 degrees of aileron deflection. The load limit is a very useable +8 to -4G.

The aircraft has been designed to be fast by turbo-prop standards with an impressive maximum speed of 370 knots. To exploit this speed advantage at low level the canopy is bird-strike resistant. The wing leading edge is designed to prevent a bird-strike from penetrating deeply into the wing structure by dissipating the energy span-wise. The zero-zero ejection seat is a Martin Baker Mk 16 with selectable command ejection options. Oxygen is supplied from an on-board oxygen generation system (OBOGS). The automatic air conditioning system is capable of keeping the cockpit environment comfortable in all climates.

I was to fly the PC-21 from the front seat supervised from the back seat by Factory Pilot Matthew ‘Fish’ Hartkop. Fish is a former US Navy F-18E/F Super Hornet Pilot and combat veteran of Iraq and Afghanistan. Fish and I had already planned our mission, stored it on a ‘brick’ and spent several hours in the simulator preparing for the mission.

Mission Data Loader – the ‘brick’

The brick is a small flat data storage device which is inserted into a slot in the front cockpit. The brick is accessed by the aircraft mission computer to obtain any pre-loaded navigation and target plans, simulated weapons load and threats.

The brick is also used to store digital data downloaded during the flight for post-flight debrief. Because the data is digital rather than traditional video it is even possible to bring up displays during debriefing that were not viewed during the sortie.
For most syllabus sorties in a school situation the brick would probably only need standard pre-flight data and mainly be used to download data for post flight use.

In practice a cache of bricks would be available for sorties within the training area. The point being that most syllabus sorties would not require any extra mission planning time than is currently required on the PC-9.

For navigation and advanced role sorties the brick would be loaded using a desktop based mission planning software. I found this software to be quick and simple to use and intuitive even for complex mission planning. Of course standard syllabus sorties could also be available for instant download in a school environment.

Our flight profile was to depart Buochs airport and immediately climb for upper air work to get a feel for the aircraft, a short low nav route through the Swiss Alps, an ILS at a local military airport and finally circuits back at home base.

The engine starts easily on internal battery. A separate battery supplies the avionics and mission systems during the start procedure ensuring that from strap-in to the end of the runway is time efficient. The nose wheel steering is on all the time via the pedals and feels natural. The take-off roll is kept straight with a little right rudder.

The Pratt & Whitney PT6A-68B 1600shp engine is controlled in a way that is unique to the PC-21. With the Power Control Lever (PCL) selected to full power the power management system limits the output to 1080shp when the aircraft is on the ground or below 90 knots airborne. Above 90 knots the available output is increased until the full 1600shp at 200 knots and above. This feature has become one of those myths around the industry and so I had anticipated that this would be a negative feature for me. In reality it is barely noticeable, especially I suspect for those of us with significant pure jet experience. Meaning this feature makes the aircraft more jet-like because it mimics the reduced thrust at lower airspeeds due to reduced ram effect. I’ve decided that I like this feature in a military trainer but perhaps that is just primacy from my days as a student on the Macchi.

Once clean the aircraft accelerates quickly through 200 knots and I climb for the upper air work. A Trim Aid Device (TAD) automatically assesses engine torque versus airspeed and makes inputs to the rudder trim to compensate. The result is the aircraft is kept pretty close to balanced with feet off the rudder pedals even during basic aerobatics. In the past I’ve not really appreciated the value of the TAD however I am now a firm believer that it is an essential feature. Turbo-prop trainers have almost direct power throughout their speed range. The PC-9/A is not fitted with a TAD so significant changes in power or airspeed requires some pro-active rudder work to keep the aircraft even close to balanced. Arguably this is a distraction for students who will never need this skill on any other ADF fixed wing aircraft.

The roll rate, which can exceed 200 degrees per second, is delightful at all speeds. With the useable roll rate, and crisp roll-stop with central aileron, I was reminded of the Pitts Special. Probably due to the relatively small aileron size there is little apparent secondary yaw. Overall the aircraft is responsive and retains energy more like a jet than the PC-9. Manoeuvring on the buffet is easily controlled with superb stick force per G. Certainly the PC-21 is not as heavy in pitch as the PC-9.

Slow speed handling is benign and stable. Stalling and spinning is unremarkable and exactly what you would expect from a well-designed training aircraft. Standard recovery procedures are immediately effective with an appropriate height loss.

Generally the behaviour of the PC-21 is predictable and the control harmony feels ‘right’ when you throw it around. Throughout the envelope the aircraft is docile and honest and well within the capability of an average ab-initio student. It is a tribute to the development team that the aerodynamic aspects of this trainer are so refined.

Cockpit Avionics

The cockpit has been devised to delineate and separate the software and associated avionics into two categories: certified ‘flight critical’ and role specific ‘mission systems’. This is a clever idea as it allows the core of the aircraft’s avionics to preserve the certification while the remaining space in the cockpit can be adapted to whatever modern needs are required without the need to undergo further expensive certification .

The ‘flight critical’ components include the Primary Flight Display (PFD), back-up flight instruments, engine and alerting displays, Flight Management System (FMS) and auto-pilot and are required for compliance with the full civilian Certification. This is all that is required to legally operate and navigate the aircraft. The ‘flight critical’ components and software are more rigid in design however in reality these certification standards rarely change.

The ‘mission system’ side of the house is intended to emulate an operational platform appropriate to the customer. This includes the two Multi Function Displays (MFD) and mission computer with the associated embedded simulation software (see Embedded Simulation below). The MFDs and open-architecture Mission Computer use flexible and robust software that allow customer requirements to be met in a timely manner. As operational platforms, role equipment and missions change this delineated concept will allow the PC-21 to adapt economically and remain an optimum training platform.

In the front cockpit there is a Head-up Display (HUD) with Up Front Control Panel (UFCP) and in the rear cockpit a HUD repeater and UFCP. All cockpit lighting and displays are NVG compatible which will in due course allow this competency to be introduced earlier. Inputs to the mission system are made via the MFD soft keys, the UFCP and hands-on throttle and stick (HOTAS).

The front and rear cockpits can be ‘split’ allowing the Instructor to make inputs to the Embedded Simulation such as driving air-to-air targets or introducing simulated failures to the student cockpit.

With the upper air work complete Fish activated our navigation route and we descend to low level. The left hand MFD is typically where moving map style nav info is displayed with primary course information on the HUD. The turn-points that we selected pre-flight on the Mission Planning System are now automatically ticked over as the computer realises that we are cutting corners. We have updated our desired time on target and a marker on the HUD indicates the speed that I should fly. As I roll the aircraft to crest a sharp ridge and dive into the next valley I recognise that I have been here before. Alpine flying must be the ultimate test for aircraft-simulator comparison and the PC-21 simulator scores high.

At low level the relatively high wing loading of the PC-21 wing ensures a comfortable ride and I become aware of how much ground I can see from the front cockpit ahead of the swept leading edge. As a student on the Macchi we used to do the later low navigation sorties at 300 knots which used to force you to lift your game. On the PC-9 a realistic speed is 210 knots. Here in the Alps the PC-21 was comfortably holding 300 knots with plenty of power to spare. Clearly the PC-21 is a realistic 300 knot low level nav platform.

Our plan to bomb the Pilatus factory is thwarted when skydivers announce their intentions so Fish demonstrates how easily the target can be updated and we simulate bombing a factory in the next valley instead. Fish then talked me through a myriad of other capabilities that can be easily called up from the mission system. I confess that as a non-fast jet operator I was struggling to understand everything that Fish was showing me – suffice to say that imagination seems to be the only limitation. Embedded synthetic simulations such as air-to-air radar and ground mapping modes will likely become increasingly important tools for training pilots and aviation specialists as customers gain experience using them.

Embedded Simulation

Pilatus has devoted significant resources to developing a practical synthetic Air-to-Air Radar for the PC-21. The concept exploits the ‘ADS-B out’ signal which includes data packets stating latitude/longitude position, altitude and vector information of aircraft within range. This signal is continually collected and calculations are made to establish a real-time position in space of multiple targets relative to our aircraft.

To display this information on the selected radar-like cockpit displays (including the HUD) the appropriate HOTAS inputs must be made as per the radar type that is being emulated. In other words, if you are pointing the radar in the wrong direction then you will not see anything. Further, the software has been so refined that limitations and idiosyncrasies of the emulated radar will be imitated. For example, if your wingman gets between you and your locked target your radar will unlock and you will have to lock it again. The PC-21 radar simulation is so realistic that you forget that it is not in fact an actual radar.

The PC-21 that I was flying has been set up to emulate the F-18 cockpit and radar. The intent is to allow the customer to shift some of the hour-intensive core competency training, such as radar proficiency and basic air-to-air intercepts, to a more cost effective platform.

The PC-21 Instructor is able to utilise a split cockpit function to make inputs into the Mission Computer without the knowledge of the student. In this way the Instructor can activate and drive simulated targets such that even a single aircraft may still participate in realistic intercept exercises. The simulated targets may also be pre-loaded via the brick or introduced directly at any time by the Instructor.

Another capability in the embedded simulation suite is the air-to-ground radar emulation. I found this to be a particularly interesting feature as I’ve always been impressed with those with the apparent ‘gift’ of air-to-ground radar interpretation. It is not a gift of course and instead a great deal of flying time on expensive operational platforms has been needed to achieve competency for many non-pilot aviation specialists.

It is realistic to expect all manner of ISR and other aviation specialist training to be possible in the PC-21.

To my mind this software driven radar-like solution is ideal for the training environment. Not only do you avoid the cost, weight, serviceability and safety aspects of operating a real radar, you have the option of inexpensively changing the radar emulation software to match your operational platforms.

The operational role training is further enhanced by embedded simulations for Electronic Warfare and Stores Management System. All of the in-flight data is stored to the brick and can be debriefed on desktop using some game quality 3D graphics and interactive controls. In the case of a multi-aircraft mission all of the bricks can be downloaded, synchronised and presented as one story. The graphic can be customised and changed to optimise the training value.

An interesting point regarding air-to-air intercepts and weapons simulation is that Pilatus has prioritised the ‘cadence’ of the events in such an exercise to match that of the emulated operational platform. Due to some clever work in the SMS software the release to impact time is similar for the simulated weapon as it would be for the top line fighter using that actual weapon. This similarity in cadence has apparently proved to be beneficial in the transition to the operational platform.

Setting up the ILS frequency in the UFCP was simple enough and I attempted to fly the approach using the HUD. After chasing myself around the HUD for a while I regressed to the PFD. The aircraft is a stable IF platform (notwithstanding my efforts with the HUD) and thanks to the TAD much easier to keep in balance than the PC-9A. I suggest that while the emphasis of advanced trainers seems to be preparation for fast jets there is much that the IFR PC-21 has in common with modern airliners that I have flown. The FMS and PFD are essentially the same and I suspect that if we had also had a play with the auto-pilot I would have mumbled something about turning on the seatbelt signs. The configuration of the certified avionics will benefit those students going into modern transport cockpits (many of which will in future also include a HUD) every bit as much as those destined for fast jets.

Back at Buochs flying circuits in the PC-21 seemed to be almost too easy and I wondered why. I realised that the PC-21 is free of two PC-9A idiosyncrasies that often made teaching circuits problematic. One is when the PCL is retarded to a torque zone where the propeller pitch angle changes abruptly and setting a specific torque becomes a major distraction for the student. The other is the constant need to make rudder inputs (and hopefully trim) to counteract the yaw caused by power changes. For the average student this battle for balance was often a distraction from the desired work cycle. By contrast setting power on the PC-21 is precise and linear and the TAD inputs keep the aircraft relatively balanced. Due to the heavier weight, and I suspect that great wing, landing the PC-21 feels far more jet-like than the PC-9.

In my first job as a Qualified Flying Instructor I taught the ‘all through’ PC-9 syllabus at 2FTS. From a simple ‘teaching a student to fly’ perspective the PC-9 was suitable to teach the whole of Wings course.

It is fair to say that the PC-21 is in some ways easier to fly than the PC-9 and just as suitable as an ab-initio military trainer. For the record, I do not advocate an all-through concept and prefer a two platform solution. My point is that the PC-21 has not become so sophisticated that it has abandoned this early phase capability. It is just as suitable as a basic trainer as it is for advanced. My instinct is that the PC-21 would be an ideal post-GFPT to LIF platform. The point of difference of the PC-21 is that it can now capably and economically eat into the space currently occupied by expensive LIF platforms – so the transition to LIF can be later after certain operational competencies are achieved. I predict that the expanding ‘training gap’ for non fast-jet operational platforms can also be closed by the PC-21.

Conclusion

The PC-21 is aerodynamically superior in the economic turbo-prop trainer class – particularly in top end performance. It is a delight to fly in all regimes and is a great ‘hands and feet’ aircraft. The PC-21 cockpit philosophy enables training to be customised to suit current operational platforms and economically adapt to future evolutions. Importantly the PC-21 is part of an integrated best practise training system that can be efficiently adapted to meet any military Pilot and aviation specialist training requirements.

Arguably the cockpit and performance of the PC-21 set it aside as the only aircraft that can not only close the gap between advanced trainer and LIF, it can actually service much of the LIF training segment. Once again Pilatus has managed to define the market rather than just follow the herd. For that they should be respected – the PC-21 is yet another winner.

Drew Searle is a former RAAF Central Flying School and 2FTS QFI with 1000 hours on the PC-9A. Searle has also flown heavy airliners for a major Asian based airline and is currently an owner/director of a flying training school and an aviation company that specialises in ex-military and advanced aerobatic aircraft. Searle is also an international Race Director for the Red Bull Air Race.