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. Engine Ice Dew Point -20-10010203040 -10 0 10 20 30 -20 Temp C 20%40%60%80% 100%

6. 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.

7. 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

8. Rime Ice White Opaque Porous Brittle

10. Clear Ice Clear Tough Dense Adhesive

11. Icing

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

13. A B Answer B

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

15. Kinetic Heating Advantages/disadvantages: Raise skin temp above ZERO 4no ice will form Warm cold objects to just below ZERO 6increase severity

16. Factors affecting severity Droplet ûsize ûtemperature ûconcentration

17. Factors affecting severity Aerofoil äshape äspeed ätemperature

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

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

21. Icing probability in stratiform cloud

22. Icing reports vs temperature

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

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

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

26. 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

27. Cloud Types and Icing

29. 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!

30. Packed Snow Leading edges Air intakes Air intakes Affects:

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

32. Hoar Frost SoftWhiteLightCrystalline

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

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

35. Rain Ice Clear Tough Dense Adhesive

36. Result of freezing drizzle on approach to Gander

37. Rain Ice Occurs when: Airframe temp. below ZEROAirframe temp. below ZERO Rain is falling from aboveRain is falling from above

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

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

40. T HT MeltingZone SuperCooledRain

41. Rain Ice ClearToughDenseAdhesive

42. 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

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

45. Pressure altitude