b-732 original, engine anti ice use

[PEI_3721]

The most relevant definition of icing conditions is that given by the aircraft / engine manufacturer – follow the SOPs. Each aircraft / engine type will have different icing characteristics and thus may have different limitations / operating procedures.

The generic ‘no ice below -40C’ has been shown to be incorrect on several occasions, and the threat of icing, particularly near Cbs (up to 15nm) is even more relevant with modern engines with their refined aerodynamics and close tolerances. Remember that ice can adhere to thin leading edges of fan blades before the thicker airframe surfaces, this is apart from any temperature / pressure changes in the intake.

Cbs can have high concentrations of water vapor at the top and in the anvil; think of this as the dirty smoke from the Cb ‘chimney’ funneling particles upward. Below the anvil, ‘the soot from the smoke’ falls out; this is often soft hail – ‘grauple’ which can represent large quantities of moisture. Hail passing through an engine will at some point melt, if this is in ‘the wrong’ place it might refreeze or stick other particles together.

Most engine types have anti-icing systems; if this is not used and the engine suffers icing then even if you do have the option for additional de-icing it might not clear the ice. Another consideration is the intake lip. Although the engine may not suffer icing, the intake could do. If the intake anti-icing is selected on late and any significant accumulation of ice is shed from the intake then it could go into the engine – shed ice lumps can be larger and denser than any bird.