TYPES OF POWER-LOSS EVENTS
The actual mechanism for ice crystal-related engine power loss takes many forms, depending on the design characteristics of each particular engine type (see table below).
|Surge/Stall*||Ice shed into compressor drives engine to surge, then stall causes rotor speeds to decay, and reducing airflow while combustor remains lit.||Thrust loss and high exhaust gas temperature.||Throttle to idle. Cycling of the fuel switch may be required to clear some stalls.|
|Flameout*||Ice shed into the combustor quenches the flame.||Thrust loss and all parameters dropping.||Ignition. Many events self-recover due to auto-relight or having the ignition already on.|
|Engine Damage||Engine blades become damaged as shed ice impacts them.||Typically no effect at time of initial damage, but damaged blades may fail later causing vibration or engine stall.||As appropriate — refer to Quick Reference Handbook.|
WHERE AND WHEN ICE CRYSTAL POWER-LOSS EVENTS HAVE OCCURRED
About 60 percent of recorded ice crystal power-loss events have occurred in Asia. Researchers speculate that this may be due to the fact that the highest sea surface temperatures are also found in this region. Higher temperature air can hold more water. There is a heavy concentration of ice crystal power-loss events between 20 and 40 degrees north latitude with a few events farther than 45 degrees from the equator (see fig. 3).
Engine power-loss events have occurred in three phases of flight: climb, cruise, and descent. However, most events occur during the descent phase, most likely because of a combination of two factors. First, for icing to occur, the ambient temperature must be below the freezing level, and therefore icing tends to occur at the higher altitude associated with the descent phase. Second, the engine is least tolerant to ice shedding at idle power, which occurs in the descent phase. Icing at high power and high altitude is possible due to the existence of high concentrations of ice crystals for long distances, such as in the anvil of a large convective storm, and the fact that ice can build up on warm engine surfaces.