Page 20 - Volume 21 Number 11

Jet Journal
The Pilatus PC-24, which is the first business jet designed to take off and land on unpaved runways, undergoes water pond testing. Although turbine aircraft undergo testing under extreme conditions, no aircraft is immune to hydroplaning, especially if not flown at the proper speed.
Landing on Liquid Ice
No aircraft is immune to hydroplaning. Know your hydroplane speed, plan ahead and use good technique when landing on wet surfaces.
by Thomas P. Turner
Alight jet overran the runway at Chicago Midway Airport in mid-July. Perhaps because the new-model jet was the first of its type delivered to a customer, images of the aftermath received widespread distribution in aviation-oriented media. Preliminary reports state:
“Information from video footage and ADS-B data suggest that the aircraft landed on Runway 31C and steered off the left side of the runway just before reaching the Engineered Material Arrestor System (EMAS) pad at the end of the runway.”
Light rain was reported at the time of the overrun, and the pavement in the photo appears quite wet. Witnesses state it had rained heavily before the jet, arriving from Philadelphia, attempted landing on the 5,141- by 150-foot (1567 by 45.7 meter) Runway 31C. The FAA’s Airplane Flying Handbook tells us:
Dynamic hydroplaning occurs when there is a film of water on the runway that is at least one-tenth inch deep. As the speed of the airplane and the depth of the water increases, the water layer builds up an increasing resistance to displacement, resulting in the formation of a wedge of water beneath the tire. At some speed, termed the hydroplaning speed (VP), the water pressure equals the weight of the airplane and the tire is lifted off the runway surface. In this condition, the tires no longer contribute to directional control and braking action is nil.
Dynamic hydroplaning is related to tire inflation pressure. Data obtained during hydroplaning tests have shown the minimum dynamic hydroplaning speed (VP) of a tire to be 8.6 times the square root of the tire pressure in pounds per square inch (PSI). For an airplane with a
18 • TWIN & TURBINE
November 2017
PILATUS AIRCRAFT PHOTO