Why we have to use ANTI ICE Below 10 degree
Bottums Up
True mmrassi, but why would one ignore such indications? And my point was more that even at seemingly high temps, one can still encounter icing.
Anecdotally I've been told by a colleague, sitting in the rear of the cabin who could hear the change in "air noise" with the selection/deselection of anti ice, that there was still a significant rim of ice on the intake lip when the anti-ice was turned off.
Anecdotally I've been told by a colleague, sitting in the rear of the cabin who could hear the change in "air noise" with the selection/deselection of anti ice, that there was still a significant rim of ice on the intake lip when the anti-ice was turned off.
Originally Posted by Douglas/Boeing 717 FCOM
General
Ice protection is provided by the airplane anti-ice systems.
NOTES: Icing can occur on the ground under the following conditions:
• OAT is less than 6°C (42°F), and
• Visible moisture is present (clouds, fog with visibility less than 1 mile, rain, snow, sleet, ice crystals, etc.) or,
• OAT and dewpoint are within 3°C (5°F) of each other or,
• When operating on ramps, taxiways, and/or runways where slush/standing water may impinge and freeze on exterior surfaces.
In flight, icing can occur under the following conditions:
• TAT is less than 6°C (42°F), and • Visible moisture is present, or
• Ice is built up on edges of windshield and other visible portions of the airplane.
Ice protection is provided by the airplane anti-ice systems.
NOTES: Icing can occur on the ground under the following conditions:
• OAT is less than 6°C (42°F), and
• Visible moisture is present (clouds, fog with visibility less than 1 mile, rain, snow, sleet, ice crystals, etc.) or,
• OAT and dewpoint are within 3°C (5°F) of each other or,
• When operating on ramps, taxiways, and/or runways where slush/standing water may impinge and freeze on exterior surfaces.
In flight, icing can occur under the following conditions:
• TAT is less than 6°C (42°F), and • Visible moisture is present, or
• Ice is built up on edges of windshield and other visible portions of the airplane.
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How about for the simple reason that people have spent years in university becoming specialists in their field (designing engines) and they've determined that it's required. Until you're as well versed in meteorology, fluid and aerodynamics just do it. We have people in our company that have barely passed high school yet are convinced that the Boeing engineered are idiots and completely wrong with regards to some of the ways we are supposed to fly the 737.
I haven't followed this thread well enough to decide if their are arguments of points or just open discussions
For what its' worth. the general concept is to control the amount of ice that forms and/or sheds. It's pretty difficult in some icing conditions to eliminate all ice since mother nature throws all kinds of stuff at you.
On the subject of inlet ice, the available amount of heat at worst conditions permits ice formations up to a point where the insulating effects of the blanket of ice against the inlet skin causes enough heat load to dislodge a layer of ice. Such layer is suppose to be handled by the engine without affecting the flight.
There are many other effects going on relative to the aircraft and other surfaces but I am trying to stay within my interpt of the OP.
For what its' worth. the general concept is to control the amount of ice that forms and/or sheds. It's pretty difficult in some icing conditions to eliminate all ice since mother nature throws all kinds of stuff at you.
On the subject of inlet ice, the available amount of heat at worst conditions permits ice formations up to a point where the insulating effects of the blanket of ice against the inlet skin causes enough heat load to dislodge a layer of ice. Such layer is suppose to be handled by the engine without affecting the flight.
There are many other effects going on relative to the aircraft and other surfaces but I am trying to stay within my interpt of the OP.
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Now my point is what if our actions beyond the book, induce damage to a system, specially in a long period of time?!
If you have time, and access to Boeing 747 manuals over the last 20 years or so, you can trace the evolution of current procedures to combat ice crystal icing on engines and TAT systems. Event,investigation,procedure,--another event,investigation ,procedure etc etc. Newer more efficient engines seem to be more prone so I don,t believe the latest procedures will be the last. Someone will be the guinea pig to initiate the next change!!
