Unpaved Extreme – The PC-24 Rolls Up Its Sleeves
The PC-24 obtained certification for use on unpaved dry dirt, sand and gravel in 2018. Our goal being to ensure the Super Versatile Jet delivers maximum flexibility into the future, a post-certification test programme was undertaken in 2019 for operations on grass, wet dirt, sand and snow. Pilatus Aircraft Ltd
The PC-24 is designed to accomplish various missions for executive travel, medevac and transport of people and equipment. Some missions are urgent, and cannot wait until the runway has dried. Comprehensive tests were therefore conducted to have the PC-24 certified for operation on all unpaved runways, in all conditions.
Getting to know your runway
To test how the PC-24 performs on wet unpaved surfaces one has to know how the runway itself reacts to the PC-24. The tests therefore also involved measuring what happens to the surface each time the PC-24 runs over it. How yielding is it? How fast does the water drain away? How long and how deep are the wheel ruts?
While this was going on, the team observed how the PC-24 behaved on the different surfaces. Did the flaps or landing gear accumulate snow or dirt and grass from the runways? Did the engines remain clear of debris thrown up from the wheels? These were all important questions in understanding how the PC-24 reacts to ensure that it can cope safely with daily operations on different surfaces in different conditions.
Gravel runways in winter
In remote areas such as Northern Canada and Alaska many gravel runways are contaminated with snow in winter. A group of engineers and aircraft mechanics travelled out to Kuujjuaq, Canada in March 2019 to test the PC-24 for operation on these surfaces. P02, the second prototype, was equipped with the instrumentation required to measure aircraft performance and with cameras to record snow and slush accumulation on the landing gear, lower fuselage and flaps.
The teams assessed and measured the impact on take-off and landing compared to dry gravel, as well as the effect on aircraft ground handling. How is the steering affected? Is the action of the brakes sufficient? How does the anti-skid system behave? Aircraft visual inspections and analysis of cameras mounted on the aircraft revealed that nothing was ingested by the engines. The results showed that the PC-24 behaved better than predicted on the snow covered gravel runway.
170,000 litres of water for a muddy field
The PC-24 has to perform well on wet dirt runways in order to operate safely in Africa and the Australian outback. For the best chance of finding suitable test conditions the team flew to Woodbridge in the UK, where initial dry dirt tests had been conducted in 2018. The tests were carried out in the conditions which might typically occur after a volume of rainfall equivalent to four litres per square metre per hour. The difficulty lay in finding a means of spraying such a large volume of water in a short time. With the help of a local farmer and a 24 metre (80 foot) farm sprayer we managed to simulate the target conditions using 170,000 litres of water per day. The PC-24 coped extremely well with this difficult scenario and all wet dirt surface tests were completed successfully.
Grass of all types
The European Aviation Safety Agency (EASA) specifies that tests to obtain certification for operations on grass runways must be performed on different types of surfaces. A number of suitable locations were identified and after site inspections, Kunovice in the Czech Republic, Poitiers in France, plus Duxford and Goodwood in Great Britain were selected.
The grass runway at Goodwood was at a high standard due to recent work, so it was perfect for tests on dry grass. A series of take-offs and landings were performed in summer 2019 to collect data for certification purposes. This tied in well with the Festival of Speed, of course! The PC-24 was prepared on location, ready and waiting to make a big entrance at this prestigious event – the only business jet to be officially approved on the new runway.
Kunovice, with its two long grass runways, a paved runway and all the infrastructure required for aircraft tests, proved a perfect location. A detailed set of tests was performed, including single-engine take-offs, engine failure and loss of ground spoilers or anti-skid, all with very good results. After a number of taxi tests on damp grass, the PC-24 was ready to affront its greatest challenge yet: take-offs and landings on wet grass. The heavy rain provided perfect conditions – and that is exactly how the results turned out: perfect! With this conclusive proof of the PC-24’s excellent performance on wet grass, the rough field test campaign came to an end.
No significant issues were noted with the PC-24 throughout the tests, on any type of surface. There was no excessive contamination of the flaps or landing gear. No debris was ingested into the engines. The pilots were satisfied with the performance of the PC-24 and all predictions were as expected or even better. With the final tests to expand the scope of operation on unpaved surfaces complete, the PC-24 has proved it is capable of rolling up its sleeves and getting on with the mission in hand, no matter what the location or the conditions. The PC-24 is now ready for operations on dry and wet runways.