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Aviation Hazards

Aviation Hazards. What we must consider: forms of icing. Packed snow Hoar frost Rain ice Engine / airframe icing. Icing. Engine Icing - can occur when the environment is above zero and is due to the intake of air cooling adiabatically Airframe Icing (our main concern)-

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Aviation Hazards

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  1. Aviation Hazards

  2. What we must consider:forms of icing • Packed snow • Hoar frost • Rain ice • Engine / airframe icing

  3. Icing Engine Icing - can occur when the environment is above zero and is due to the intake of air cooling adiabatically Airframe Icing (our main concern)- supercooled droplets freeze on the aircraft body

  4. Engine Ice Due to: 1. Decrease of pressure inside engine manifold 2. Extraction of latent heat due to vaporisation

  5. ICING TYPES: • Rime Ice: Rough, milky, opaque ice formed by the instantaneous freezing of small supercooled water droplets. • Clear Ice: A glossy, clear, or translucent ice formed by the relatively slow freezing of large supercooled water droplets.

  6. Airframe Icing Small supercooled water droplet • Freezes quickly on contact with airframe Large supercooled water droplet • Begins to freeze on initial impact • Latent heat release as droplet freezes

  7. Rime Ice WhiteOpaquePorousBrittle

  8. Clear Ice ClearToughDenseAdhesive

  9. Icing

  10. 150 KT A 150 KT B Question: Which airframe will have the greatest icing?

  11. Answer B 150 KT A 150 KT B

  12. Kinetic Heating Increased pressure at leading edges Friction between aircraft skin and atmosphere Generated by:

  13. Kinetic Heating Raise skin temp above ZERO • no ice will form Warm cold objects to just below ZERO • increase severity Advantages/disadvantages:

  14. Factors affecting severity Droplet • size • temperature • concentration

  15. Factors affecting severity Aerofoil • shape • speed • temperature

  16. Effects on Aircraft Aerodynamics- shape altered All up weight - increases Engine- intakes may become blocked Undercarriage- retraction problems Control surfaces - may jam or become stiff Pitot tubes - blocked Communications- affected Vision- impaired Vibration- due to uneven loading

  17. Airframe Icing • Requires supercooled droplets • Airframe icing is most efficient when the cloud droplets are between 0 0C and -15 0C • Below -20 0C only very small supercooled droplets can exist • Large supercooled droplets are a greater hazard as they spread out to a greater extent

  18. Icing probability in stratiform cloud

  19. Icing reports vs temperature

  20. Icing in stratiform cloud -3 C 0 C 4 C

  21. Accretion Depends on: • Aircraft characteristics • Cloud type • Length of time flying through the cloud, (especially significant for layered cloud)

  22. Forecasting icing • Types of cloud • Temperature of cloud • Horizontal extent of cloud • Changes in airmass characteristics

  23. Icing • Entrainment of dry air at the top of a cloud will reduce the water content and therefore its icing ability • Vertical motion within cloud will increase the liquid water content significantly • Strong vertical motion in convective clouds produce the most severe icing • Vertical motion due to fronts or orography can also give severe icing problems

  24. Cloud Types and Icing

  25. Cloud Types and Icing

  26. Further points • Maritime clouds have fewer, larger droplets • LWC in stratiform cloud can be up to 10X lower than in convective cloud • Icing layer usually around 2-3000ft thick and is seldom >5000ft • Autopilots can mask the effect of icing until it is too late!

  27. Packed Snow Leading edges Air intakes Affects:

  28. Packed Snow Occurs when: • flying through wet snow • in or beneath clouds • with temperature near ZERO

  29. Hoar Frost Soft White Light Crystalline

  30. Hoar Frost Airframe temperature below ZERO Air is cooled below dew point Forms in clear air when:

  31. Hoar Frost can occur • 1. Aircraft parked outside on clear winter nights. • 2. Rapid descent into warmer (clear), moist air, (cold soak). • 3. Frosty morning with warmer, moist air above.

  32. Rain Ice ClearToughDenseAdhesive

  33. Result of freezing drizzle on approach to Gander

  34. Rain Ice • Airframe temp. below ZERO • Rain is falling from above Occurs when:

  35. Rain Ice Rapid descent(after prolonged flight at high level) Ahead of a warm front Circumstances:

  36. Plan view 0 C isotherm Warm Air 0 C isotherm Cold Air Cross Section

  37. HT 0 C isotherm Melting Zone Super Cooled Rain T 0 C isotherm

  38. Rain Ice Accumulates quickly! Clear Tough Dense Adhesive

  39. Moderate or Severe Icing may be expected in: Cumuliform clouds Nimbostratus Active cold fronts Stratocumulus formed from Cu Over hills and mountains Ahead of some warm fronts

  40. Summary • Be thoroughly aware of customer practices • Examine cloud type / structure carefully • Main concern- helicopters / light aircraft • Good communication with flyers helps

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