FLIGHT TEST: Pilatus PC-6

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Even good things can get better, and by upgrading the cockpit with the capable Garmin 950 integrated display system, Pilatus has found a way to improve its classic PC-6 piston single.

The Garmin 950 has the autopilot as a separate function/customer option rather than integrated within the system, otherwise it is virtually identical to the successful Garmin 1000 system, which is widely fitted in types including the Cessna 172, Diamond DA42 and Daher-Socata TBM 850. All these display systems are supported by Garmin worldwide.

The Garmin system replaces the PC-6's analogue cockpit with two 10.4in (265mm) LCD screens for the electronic flight instrument system pilot flight display, navigation and multifunction displays and supporting GPS PR-NAV navigation, WAAS GPS approaches, instrument landing system, VOR, 8.33MHz VHF radios and S-Mode transponder.


A classic aircraft now has the added benefit of a digital cockpit. Picture: Pilatus 

Additional customer options include satellite telephone, upgraded special mission systems power generation/distribution, TWAS, TCAS and weather radar, among others. Garmin intends to add synthetic vision system (SVS) type terrain overlay and terrain referenced airfield location/orientation, on to the 950 primary flight display at its next software upgrade.

The feasibility study for an avionics upgrade began in 2008 after a contract was placed by the French air force to improve its fleet of five PC-6s. The 950 avionics upgrade has been carried out in partnership with Kuerzi Avionics in Switzerland and it gained its European Aviation Safety Agency-approved supplementary type certificate in January.

The 950 STC costs around $295,000 and requires an aircraft down time for retrofit of around five weeks. Virtually all PC-6 Turbo Porters flying today (around 350) are eligible to have the 950 STC retrofitted as long as they have had the "H4" strengthening modification (maximum all-up weight 2,810kg/6,200lb) and are fitted with an electric trim system.

All new PC-6 Turbo-Porters will be manufactured with the Garmin 950 as standard and Pilatus is aiming for a production rate of at least 12 aircraft a year at its Buochs facility. European and US markets use the PC-6 primarily in the recreational sport support role (free-fall parachutists, off-piste skiers, and so on) but the short take-off and landing and rugged terrain take-off/landing capabilities of the aircraft, now allied to the accurate GPS navigation and SVS display of the Garmin 950 STC, also open up a new world of possibilities for the PC-6 for military special forces or police surveillance/enforcement roles. Other strongly emerging markets for the aircraft are in Brazil, China and South-East Asia in support of remote civil settlements or industrial sites at remote locations.

The PC-6 has a payload of over 1,000kg at maximum internal fuel, a cabin volume of over 3m3 (105ft3) and full length sliding doors on both sides of the cabin. With an all-new purchase price of $1.9 million, Pilatus says that the PC-6 represents a total cost of just 20% compared with the cost of a helicopter with similar load-carrying capabilities. The PC-6 has a similar order of magnitude reduction in direct operating costs when compared with the same helicopter type.

Ground roll of the PC-6 at maximum take-off weight (2,800kg) is 197m (646ft) and landing roll at maximum landing weight (2,660kg) is 127m. Landing videos (available on YouTube) show the PC-6 easily coping with landing on 15-20° up-slope airstrips and into jungle clearings that appear to be no more than a footpath.

I believe the 950 upgrade offered as an STC represents shrewd thinking by Pilatus as it modernises the aircraft overnight at very low cost to an operator. It could also transform the aircraft's marketing appeal and substantially reduce avionics maintenance costs, while an STC approval is much simpler to obtain than a comprehensive aircraft upgrade that the PC-6 does not need, but would have required a complete new aircraft certification programme.

EVALUATION
My evaluation took place from Buochs airfield in ISA conditions and, initially, light winds. My aircraft was the PC-6 company demonstrator, HB-FNI, used by Pilatus for 950 STC development.

The aircraft was fitted with under-wing ferry fuel tanks (of 390kg total capacity, but empty for the assessment) and a four-bladed propeller. With about 500kg (maximum internal) wing fuel, two pilots and an empty cargo compartment, our take-off mass was roughly 1,950kg. My safety pilot was Reto Aeschlimann, the Pilatus chief test pilot and also a PC-6 project test pilot.

 
Pilatus began a study into the PC-6 upgrade two years ago. Picture: Pilatus

The role I set myself was to be that of a "low-time" PC-6 pilot hired to fly the aircraft in mountainous areas. My objectives were twofold: firstly could I manage the 950 system easily in all its modes while flying single pilot in probable turbulence and possibly having to manoeuvre hard along my route? Secondly, would the new displays combine to be a real workload reducer and safety improver for any pilot when faced with possible poor weather and unforgiving terrain?

Changing weather conditions at Buochs meant an immediate take-off after my arrival at the Pilatus facility. I would fly the complete evaluation without any chance for any Garmin 950 ground schooling, so the ease with which I could manage the system and assimilate the display information would be an accurate reflection on the success of the STC integration within such a utility aircraft.

Entering the PC-6 Garmin 950 STC cockpit, I was immediately impressed with how clean and uncluttered it looked, with a lot of clear space on the vertical instrument console face for additional optional equipment. The cockpit feels like being inside a military vehicle, but one that is precision engineered and beautifully finished.

The full-width cockpit shelf holds the propeller control (left), throttle (central) and condition lever (right) in a central console. The 950 system preparation/flight planning is performed on internal battery power and there is no memory drop out or screen loss during engine start. However, Pilatus is considering fitting an "essential services" power switch to reduce electrical drain if the 950 system is required to be powered for extended periods by the battery on the ground before engine start.


The PC-6 has a cabin volume of over 3m3 and two sliding doors. Picture: Pilatus 

The 950/1000 systems combine the functions of flight management system control display unit, remote maintenance unit, pilot display panel, guidance display panel, electronic flight bag and system synoptic panel into the rotary switches and push buttons located on the sides and bottom of the two LCD displays.

There is no QWERTY keyboard, no trackball/crosshair designation or control display unit scratch pad to write into. Menu lists are selected, data fields highlighted and data then entered via the rotary knobs "on screen" before insertion.

This takes a little bit of getting used to if you are familiar with the Honeywell or Rockwell Collins systems found on most business jets, but the basics are quickly mastered and I estimate a one or two-day 950 ground school course would be perfectly adequate training for a pilot unfamiliar with an EFIS glass type cockpit. Once understood the 950 gives a wealth of information including being able to tailor the displays to a pilot's individual preference and retain that preference in memory.

The left-hand screen is always used as the primary flight display and the right-hand screen as the navigation/multifunction display. In the event of screen failure a "composite" PFD/MFD can be shown on the remaining live screen with flight plan and/or terrain plan displayed as a picture in picture.

 
The cockpit feels like being in a military vehicle but one that is beautifully finished. Picture: Pilatus

For take-off and landing, the flap position and rudder/aileron/elevator trim bar indicators displayed on the navigation/multifunction displays can be transferred across to the primary display as a composite picture to be directly in front of the pilot, although this drives both screens into composite mode if both are live.

The flap position, fuel contents, rudder/aileron/elevator trim position bar type indicators on the ND/MFD were closely spaced and smaller than I would have liked, but still completely adequate for the role and a typical limitation in such an off-the-shelf system. Although the PC-6 only has a narrow cockpit upper glareshield, the 950 displays are perfectly readable in bright sunshine conditions.

The 550shp (410kW) Pratt & Whitney Canada PT6A-27 engine is quick and simple to start. At 15% NG the condition lever is placed from cut off into low idle. With the engine stable the propeller lever is placed from feather into coarse.

I was ready to taxi less than 45s after start selection. Thereafter, in all flight modes, the aircraft is normally flown single lever, with only the throttle used for thrust control. Only if the pilot wishes to prepare for a possible go-around from a steep approach into critically rising terrain would the propeller lever be set to fine and the condition lever set to high idle.

 
The P&WC PT6A-27 engine is quick and simple to start. Picture: Pilatus

During taxi, the forward field of view over the long tapering nose was better than I expected and there is no need normally to weave the aircraft to clear the groundpath. The tailwheel is set to free castor and the mainwheel brakes dabbed as the following castoring tailwheel makes the aircraft very responsive to turn. For take-off and landing the tailwheel is locked central to prevent directional overcontrol (the PC-6 demonstrated crosswind is shown at 16kt/30km/h), but it then requires more determined individual brake applications by the pilot to stay straight if the aircraft swings.

For take-off, the control column was held just rearwards from neutral and full power applied and regulated by the pilot with reference to the torque gauge shown on the ND/MFD. There was little swing and, as the power stabilised and the vertical airspeed indicator tape display started to register at an indicated airspeed of around 38kt, we seemed to lift off vertically at 45kt without me having to rotate the aircraft or apply any backstick force. It was the shortest powered aircraft take-off I have ever experienced except for the BAe Harrier.

I found the PC-6 easy, pleasant and accurate to fly. The control forces were light and well harmonised. The aircraft felt nimble in roll with a sustained roll rate of around 60°/s. Strong adverse yaw was exhibited with any large lateral stick input, but this was quickly corrected by the fin.

I did, however, long for an old-fashioned, big, "fluid tube" type slip ball to aid my rudder inputs and supplement the rather small "split pyramid" roll/yaw indicator in the primary display. I found the display easy to interpret and especially liked that the vertical speed tape was in 5kt increments allowing for accurate airspeed monitoring.

This was especially evident at full flap and idle throttle where the aircraft could be held precisely at an indicated airspeed of 80kt in a steep approach at 20-25° nose-down pitch.

 
Collins found the PC-6 easy, pleasant and accurate to fly. Picture: Pilatus

SITUATIONAL AWARENESS
I believe the future expected Garmin 950 upgrade, which will display SVS terrain overlay and airstrip orientation directly on to the primary display, will grant the PC-6 pilot another increase in situational awareness.

On the ND/MFD, I found engine and ancillary system monitoring to be clear and straightforward. Standard tasks such as radio or navigation aid frequency selection were routine and, although ND selections are done "cross cockpit" for the pilot (always seated on the left), the cockpit shelf provided an excellent right arm rest when turning rotary knobs or selecting menu keys.

Again, I especially liked the ND depiction of terrain, controlled airspace, geographical features, danger areas, and so on, which are all clearly defined on a wide, bright screen and one where the range scale is fully variable. Older EFIS types have much larger, fixed, range scale "jumps".

The unexpected early arrival of a massive thunderstorm over Buochs forced us into an unplanned, medium level (5,000ft AGL), diversion to Altenrhein, on the Bodensee about 120km (65nm) north-east of Buochs. This gave me an excellent opportunity to explore some further modes of the navigation display, including flight plan construction, direct-to navigation and the EFB type functions that not only list airfield details but will automatically reselect the appropriate radio frequencies for the pilot if required. What was obvious was that the Garmin 950 system endows a massive modern avionics capability to any aircraft and all within an intelligent and compact package.

Once the thunderstorm had passed Altenrhein we returned to Buochs at dusk in light rain and poor visibility. The conditions and the terrain put the Garmin 950 to the ultimate test as I had done no pre-flight planning, but used the navigation display to fly home at around 1,000ft AGL and under visual flight rules.

Despite the poor conditions I found the navigation display inspired total confidence with respect to the amount of information it provided without cluttering the screen and, through this, aid my situational awareness in a part of Switzerland I had never seen or flown over.

The terrain map overlay gave me a fully defined picture of which valleys ahead and to the side were the ones I could use for "escape" and which ones were "dead ends" should the weather worsen.

At no time did I lose the additional topographical ND information of roads, railways, rivers, lakes and towns. On top of this I had a completely clear picture of the lateral and vertical controlled airspace around me surrounding the military, civil airfields and international airports (Zurich) we passed en route.

The Garmin 950 made a complex navigation route back to home base feel almost relaxed. My final approach to Buochs was by using the ND to position the aircraft on to Runway 07 visual finals from behind the mountain immediately to the east of the field.

I celebrated my arrival with a typical test pilot, poorly executed, three-point landing.

CONCLUSION
The refinement but simplicity of the Garmin 950 STC is unquestionably an ideal match to the ruggedness of the PC-6. My objectives were clearly answered from my short evaluation - the Garmin 950 will be easy to manage for a PC-6 pilot when airborne (after a short ground-school training course), be easy to view and be easy to interpret.

Additionally, the Garmin 950 STC endows the PC-6 pilot with a quantum leap forwards in terms of workload reduction and safety improvement in comparison with the old analogue cockpit, and all at an affordable price.

Pilatus describe the PC-6 as a niche aircraft, but with the navigation accuracy and situational awareness capability that the Garmin 950 STC now delivers and the future display enhancements it can support, I think this description undervalues the aircraft.

A police force or an air force could buy and operate five PC-6s for the same price as one helicopter of similar load-carrying capacity and still be able to land/take off or insert/extract personnel in 99% of planned situations in the most rugged and hostile of terrains.

It was a pleasure for me to fly and evaluate such an iconic and superb STOL utility aircraft. That the PC-6 Turbo Porter is still in production after 50 years is ample testimony to the rightness of its initial design.

Beyond this, however, the Garmin 950 STC propels the PC-6 into the 21st century and, without exaggeration, I believe it means that the aircraft could still be in production in another 50 years. Once again I was highly impressed by a current Pilatus aircraft type.

If versatility times capability times affordability were a utility aircraft equation then the conclusion now equals the PC-6 Turbo Porter upgraded with the Garmin 950 STC.