Ice Crystal Icing John McGrath, Gulfstream Flight Operations June 26, 2017 Presentation Title Ice Crystal Icing – What is it? • High altitude water is likely to be frozen ice particles not supercooled liquid drops • Icing conditions previously referred to conditions where supercooled liquid drops adhere to cold airframe surfaces – Typically altitudes 22,000 feet and below • Ice crystal icing does not affect cold airframe surfaces – Only some engines 1 Gulfstream Proprietary Information Ice Crystal Icing Ice Crystal Icing – What is it? • Convective activity lofts ice crystals in significant quantities into the upper atmosphere – As small as 40 microns, consistency of flour • No airframe icing • Invisible to aircraft radar and ice detectors • Crews unaware of potential hazards • Greatest hazard is loss of engine power – Over 100 power losses attributed to ice crystal icing over the past 2 decades 2 Gulfstream Proprietary Information Ice Crystal Icing Ice Crystal Icing – What is it? • Ice crystals previously thought to be harmless • Theory - crystals would bounce off airframe and engine surfaces with no accretion • Current analysis – ice crystals can partially melt due to compression effects – Pass through the engine fan section – Enter the core and create a film of moisture on the forward stator vanes – Moisture traps additional crystals – End result is the ice buildup is shed into the compressor causing engine surge, stall and flameout 3 Gulfstream Proprietary Information Ice Crystal Icing When do the events occur? • Study of 46 incidents for which significant data is available revealed common characteristics • Most events occur in the summer months – Relatively warm air – Above 20,000 ft – Near or above convective activity – Visible moisture with light/moderate turbulence – Deviations around thunderstorms or areas of significant precipitation shown on the radar 4 Gulfstream Proprietary Information Ice Crystal Icing When do the events occur? • Twenty eight incidents occurred during descent • Seventeen incidents in cruise • One incident in climb • Power losses at high power indicate extended exposure to very high concentrations of ice crystals • Power losses during descent are explained by low thrust settings with minimum airflow through the engine – Compressor section is more susceptible to ice accretion at low power due to reduced temperature 5 Gulfstream Proprietary Information Ice Crystal Icing Clues On Ice Crystal Icing • Some power losses occurred during conditions reported as “heavy rain” • Based on reports of rain hitting the windshield – Some reports were that the sound was different than rain – With landing lights on, the airborne particles reported as looking different than rain • Another clue is anomalous TAT indications – Erratic and possibly erroneous TAT indications are caused by ice crystals building up on the TAT probe which blocked air flow through the probe – 35 of the power loss event reported TAT anomalies prior to the loss of power 6 Gulfstream Proprietary Information Ice Crystal Icing Types of Convective Weather • Non-classic convective (80% of ICI events) – Weak updrafts – Regions of decaying convection – Regions of high ice water content (HIWC) aloft – Lacks reflectivity at flight level, making it more difficult for pilots to identify HIWC Possible 7 Gulfstream Proprietary Information Ice Crystal Icing Types of Convective Weather • Classic convection (20% of ICI events) – Vigorous updrafts – Typically found over land – Moderate to heavy radar signatures present up to high altitudes – Core areas and danger zones detectible so the flight crew can avoid them HIWC Possible 8 Gulfstream Proprietary Information Ice Crystal Icing Where do the events occur? • Areas of heavy returns at high altitude • Broad areas of decaying convection 9 Gulfstream Proprietary Information Ice Crystal Icing Where do the events occur? • Most events have occurred in tropical and subtropical regions of the world – 30 degrees south and 30 degrees north latitude – Warm, humid surface air – Warmer temperatures = more moisture – Higher latitudes in summer months – 60% of ICI events in Asia 10 Gulfstream Proprietary Information Ice Crystal Icing Characteristics of ICI • High-altitude, cold temperature • Aircraft in the vicinity of convective clouds – Thunderstorms, squall lines, or tropical storms – Storm life cycles ranging from several hours to over 24 hours • Visible moisture • Light-to-moderate turbulence • Weak to modest updraft velocities • Precipitation on heated windscreen 11 Gulfstream Proprietary Information Ice Crystal Icing Characteristics of ICI • Moderate to heavy rain is present below the airplane – Amber and red radar returns – Little or no returns at fight level – Radar reflectivity 5% of average size raindrops • No ice detector response • No significant airframe icing • No hail reported • No lightning reported 12 Gulfstream Proprietary Information Ice Crystal Icing How could ICI affect Our Aircraft • Erratic and possibly erroneous TAT indications • Erratic and possibly erroneous airspeed indications • High LP vibrations on GV and G550 have been reported – Suspect ice on spinner fairing • No G650 reported ICI vibration incidents – BR725 has single piece nose cone • No GIV/G450 reported ICI vibration incidents – 5 G-IV and 1 G450 events of fan blade icing 13 Gulfstream Proprietary Information Ice Crystal Icing G550 High LP Vibration 14 Gulfstream Proprietary Information Ice Crystal Icing Recommendations for Flight Near Convection • No practical way to avoid all ice crystal conditions – Crystals may not be detected by aviation radar • Normal thunderstorm avoidance procedures may help • Avoid convective regions by at least 20 nautical miles • Fly upwind of the cell – Avoid the spreading anvil downstream – Limit exposure to high ice particle concentrations 15 Gulfstream Proprietary Information Ice Crystal Icing Recommendations for Flight Near Convection • Avoid flying in visible moisture over storm cells – Visible moisture at high altitude must be considered a threat – Even with no radar returns, there may be significant moisture in the form of ice crystals at high-altitudes • Utilize radar antenna tilt function to scan reflectivity of storms ahead – Heavy rain below likely indicates high concentrations of ice crystals above 16 Gulfstream Proprietary Information Ice Crystal Icing Recommendations When ICI is Encountered • Select cowl anti-ice ON when SAT is less than 10 degrees and convective activity is encountered or overflown • If increasing EVM indications occur in VMC turning the cowl antiice ON may remedy the situation • If increased EVM persists, perform ice shedding procedure • If ice shedding procedure is not effective: – Reduction of power to control vibrations – Descend to warmer temperature may be required • If air data information is affected, refer to AFM procedure 04-16-20 Suspected Erroneous/Unreliable Airspeed Indications. • LP vibrations above .80 require a post flight inspection 17 Gulfstream Proprietary Information Ice Crystal Icing Ice Crystal Icing PROPRIETARY NOTICE THIS DATA AND INFORMATION CONTAINED HEREIN IS PROPRIETARY DATA OF GULFSTREAM AEROSPACE CORPORATION. NEITHER THIS DATA NOR THE DATA CONTAINED HEREIN SHALL BE REPRODUCED, USED, OR DISCLOSED TO OTHERS WITHOUT THE EXPRESS WRITTEN AUTHORIZATION OF GULFSTREAM AEROSPACE CORPORATION. Gulfstream Proprietary Information
