Some thoughts;-
- Global warming is put aside, but not eliminated (see refs).
- Engine design. Problems were reported with aircraft engines as early as 1989/90. Serious research and regulatory activities started in the mid – late 90s after some aircraft suffered multiple engine rollbacks.
Modern engines use very high efficiency aerodynamic components with close tolerance fittings. Whereas older designs could suffer some ice accretion without obvious problems, the new systems degrade rapidly. An analogy is with super-critical wing sections suffering from ‘bug splatter’.
Even so, larger engines appear to manage ice crystal icing easier than smaller engines, but performance/degradation depends on individual designs – see centrifuge issues below. In addition, use of internal anti-icing heat adds to the possibility of melting some crystals providing the ‘glue’ (freezing water) for other crystals to stick together. With older/unheated engines the crystals tended to bounce off (possible origin of no airframe ice [accretion] below -40C).
- Changes in design and location of probes. TAT probes encountered problems in similar timescales as engines (also some reports of A310 / Concord pitot problems – flight test?).
New pitot designs perhaps did not consider ice crystal capture/build up, or they enhanced the particle melting ‘glue’ aspects.
Airframe aerodynamic efficiencies resulted in probe locations where there is more catchment of ice crystals. High curvature flow around the aircraft nose tends to centrifuge out the heavier water / crystal content, but smoother low curvature flow results in more lightweight ice crystals entering the tube; again specific design issues with probe, aircraft, and location.
- Avionics. Availability of modern colour radar may encourage crews to fly closer storm centres than previously. The older ‘cloud and clunk’ WXR gave a single boundary defined by skilful use of tilt/gain – stay out of this area and a bit more; new radars have several ‘automatic’ colours thus a choice of acceptability – keep out of the red, but yellow / green may be acceptable. This false reasoning has been reinforced with sales talk of ‘cleaver’ electronic features; pilots overlook this and also that most aircraft WXR do not detect ice. Ice crystal conditions at best might only show as a green zone.
Thus the exposure to ice crystals - frequency of encountering the conditions and the duration in the conditions has increased.
- Changes in operational complexity – airspace limits, e.g. does RNP / RVSM (or crew’s perception of safety limits ) increase the probability of encountering areas of Cbs. Crew’s awareness of the icing threats depends on training and incidents reported. Modern airframes appear to tolerate more icing encounters – better design / efficient systems, but this may not apply universally to all aircraft or all aspects of a single type.
The industry appears to be less aware of icing risks; have we forgotten many of the rules of thumb – don’t fly in/under the anvil of Cbs.
Complacency?
http://icingalliance.org/meetings/RI...ersion_nss.pdf
IASCC - International Air Safety & Climate Change conference - presentations, workshop 1, day 2, Eric Duvivier, EASA - "High Altitude Icing Environment"
http://www.ukfsc.co.uk/files/Safety%...Oct%202009.pdf