Now let's talk about lightning — Page 263, Lesson 236

I want to walk you through the risks and realities of lightning in thunderstorm operations. We're picking up from the point where we've already discussed that if you absolutely cannot avoid penetrating a thunderstorm area, you're accepting certain risks. But here's the critical warning: failure to recognise or anticipate icing conditions, failure to use your de-icing or anti-icing equipment properly, equipment unserviceability, or extended flight through a storm area — any one of these will considerably increase the risks involved. So the message is clear: even if you have to go through, you must be fully aware of the icing threat and ensure your equipment is working and correctly used, and you must minimise your time inside the storm. Now let's talk about lightning. Lightning can occur both within and away from cumulonimbus clouds. The discharges take place in several ways: within the cloud itself, between neighbouring clouds, commonly between a cloud and the ground, and less commonly from the top of a cloud upwards. So it's not just cloud-to-ground — most lightning is actually within the cloud. Here's a key operational fact: most recorded lightning strikes have occurred at levels where the temperature is between +10°C and -10°C. That temperature band corresponds to about 5000 feet above or below the freezing level. So if you're flying near the freezing level, you're in the statistically most likely zone for a strike. Some risk also exists outside this band, particularly at higher levels, so don't assume you're safe just because you're well above or below that band. Strikes are either electrically positive or negative in polarity, although the polarity of the strike is not evident to you at the time it happens. You won't know which type hit you until afterwards. But here's what matters: positive polarity strikes are likely to be the more severe — they cause more damage to the aircraft. Recent investigations have shown that the North Sea is an area prone to a higher than normal frequency of positive strikes, although the overall frequency of strikes per flying hour is similar to that in the rest of Europe. So if you're flying over the North Sea, the total number of strikes isn't higher, but a greater proportion of them are the more damaging positive type. What can indicate conditions conducive to a positive strike? The presence of soft hail has been associated with some positive strikes. So if you're seeing soft hail, that may be a warning that the conditions are right for a positive polarity strike. For further information regarding lightning and aircraft engines, you should refer to AIC 29/2004 (Pink 64) — 'Engine Malfunction Caused by Lightning Strikes'. That's a specific advisory circular you'd want to have in your knowledge base. Now, what actually happens when an aircraft is struck? The brilliant flash, the smell of burning, and the accompanying explosive noise can be alarming and distracting to the pilots. That's a very human reaction — it's loud, bright, and startling. But here's the sobering reality: a serious accident involving a large transport aircraft was investigated, and the report stated that it was due to a lightning strike causing ignition of vapour in the region of fuel tank vents. So lightning can ignite fuel vapour. However, fatal accidents due to lightning strikes have fortunately been very few, and most aircraft receive only superficial damage when struck. So while it's a serious event, the statistical likelihood of a fatal outcome is low. We'll continue with the effect of lightning strikes on direct reading magnetic compasses and other systems in the next part.