SAE AIR 1335A-2000 pdf download Ramp De-Icing
7.4 Icing Conditions for Jets 1 : Jets are less susceptible to icing problems than piston aircraft because:
7.4.1 The greater climb capability of jetliners reduces length of time they are likely to encounter icing conditions. These high rates of climb enable a jet transport to fly through thin stratus type clouds fast enough to prevent heavy ice build-ups. A 2,000 f.p.m. rate of climb carries an airplane through the average layer cloud in about a minute and a half, and through the thickest in about three and a quarter minutes. Thicker cumulus clouds are often avoided due to turbulence, flying around them is the standard procedure.
7.4.2 The speed of the jets reduces icing severity and the extent of conditions under which icing will occur. An airfoil passing through air converts the impact energy into an air temperature rise which increases the skin surface temperature. This temperature increase is commonly referred to as the “ram rise”. Thus, the jetliner’s speed enables it to develop a significant ram rise and this reduces the extent of icing effects. As an example, at sea level an airspeed of 260 knots increases the wet skin temperature to 32 °F (0 °C) when OAT is 24 °F (-4.4 °C). Ram rise thus effectively reduces the thickness of the icing layer. In many cases ram rise is sufficient to prevent icing all the way through many icing layers that would affect piston planes.
7.4.3 Jet liner’s cruise-altitudes are far above most icing conditions. At these altitudes temperatures are so far below freezing that moisture almost always exists as ice and the air is so dry that icing is seldom possible except in tropical thunderheads.
7.4.4 The power of high-performance jet engines reduces the significance of icing drag. That is, a given amount of drag from ice-accretion affects a jet transport less than its piston counterpart because of the jet’s greater thrust margin. Since piston aircraft operate near their productive limit, they are more affected by icing drag or drag due to some other cause.
7.4.5 The airfoils of jets have longer chord lengths and are swept back – both of these factors reduce the drag increment from a given accumulation of ice at the leading edge.
8. IMPROPER DE-ICING:
8.1 “Aileron and Rudder Nibble or Vibration Enroute” – An Actual Occurence: “A short time after departure from Montreal, I felt an aileron “nibble” or “flutter” through the control wheel. I mentioned this to the co-pilot who stated that he did not have too much evidence of it in his control wheel. After being airborne 30 to 45 minutes, the aileron nibble became more evident and a tail vibration or nibble was felt through the rudder pedals. This time the co-pilot acknowledged the condition to be present both in feel and by observing the control wheel oscillating rapidly, as well as the rudder pedals oscillating back and forth in short vibratory movements. Reducing the airspeed 30 to 50 knots, by engine power reduction, corrected the vibration which did not reappear during subsequent descent and landing at scheduled Toronto enroute stop.
SAE AIR 1335A-2000 pdf download
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