Pilot's Guide to Avionics 2011-2012 - (Page 33)

PILOT’S GUIDE itself that generates static electricity, which lightning releases . Few aspects of aviating match the discomfort accompanying a full-on encounter with a storm producing these two co-conspirators of lightning and turbulence . Turbulence doesn’t automatically portend lightning . Other conditions cause turbulence: the shearing action between layers of air moving in opposite directions; mountain-spurred turbulence from high winds; the boundary layer announcing the approach of a front . While seldom as savage as the turbulence of a lightning-laden thunderstorm, these types of turbulence also justify avoidance because of the discomfort they create . Degrees of Discomfort We seldom bat an eye at light turbulence — when the airplane experiences only slightly erratic changes in altitude or attitude . Should conditions progress into light chop, the ongoing arrhythmic bumps it brings might wear on us . The rapid jolts and noticeable displacement of moderate turbulence should be a wake-up call to make a new decision lest conditions progress to moderate chop with more frequent and pronounced arrhythmic bumps . We quickly recognize encountering severe turbulence, with large degrees of displacement and wide swings in airspeed . Touch the edge of extreme turbulence, and the feeling most coveted is the relief of escaping to smooth air . Typically, those higher levels of turbulence come in the vicinity of a significant storm: Level 3 and above . But pilots can find themselves in the maelstrom with little warning, despite forecasts, even while turning to avoid similar conditions elsewhere . While we generally see something of lightning’s output, we can only infer the location of turbulence, in part because we’ve learned of the conjoined nature of turbulence-generated lightning . This has made detecting lightning a primary way of avoiding both electric and turbulent encounters . Risks Abound in Those Bumps Any encounter with the violence of severe or extreme turbulence instills an appreciation for the chaos of the atmospheric churn . Ignoring its power brings significant risks . Turbulence is a main cause of injuries on airline flights . The injuries generally result from a sudden, unexpected encounter with conditions that announce themselves by tossing unrestrained humans against the ceiling until gravity resumes control and drops the unfortunates . The National Transportation Safety Board studied a seven-year period — 2003 through 2009 — and found 80 incidents of turbulence seriously injuring one or more people on the affected airplane . Earlier this year, airliner captains twice diverted toward treatment for the injuries of passengers tossed about the cabin . In one instance, 30 people on one airliner suffered injuries . The plane itself faces risks depending on how the pilot handles a rough-weather encounter . Go too fast in too much turbulence and the airplane can break up; go too slow and control becomes more difficult . Unfortunately, remaining grounded is the only definitive way to avoid turbulence . With its power to damage electrical and electronic components while burning holes in the airframe, lightning sounds scarier than turbulence . The emphasis, however, should be on joint-avoidance efforts, and this is where technology can help your customers . The symbiotic relationship between turbulence and lightning underpins one of the older, more useful onboard and ground tools for storm avoidance: the spherics device . Thanks to advances in radar displays, digital processing, Doppler radar and lasers, we are closing in on tools to detect turbulence absent electrical discharges . A Hazard-Avoidance Hat Trick Although we seldom tune in AM radio these days, it serves as an omni-directional lightning detector, picking up the burst of radio-frequency energy that occurs with lightning strikes and “playing” this energy as audible bursts of static . Building on the phenomenon, the avionics industry offers pilots several systems capable of detecting both the soft, aerially discharged pulses of airborne turbulence and lightning . A spherics device works on the same principal: Listen for the same radio-frequency emissions of lightning strikes that produce static on AM radio . Because of the sensitivity of these systems, they serve as much as a tool for avoiding turbulence — the harbinger of static-electrical buildup — as for the lightning itself . A spherics device uses a sensitive directional antenna to generate a bearing to the radio frequency; signal processing of the lightning signal to calculate distance; and convert it into a display indication . The spherics hardware available for aircraft offers sensitivities, accuracy levels and features Continued on following page… - 33 -

Pilot's Guide to Avionics 2011-2012

Table of Contents for the Digital Edition of Pilot's Guide to Avionics 2011-2012