Thunderstorms — Page 257, Lesson 213

I want to walk you through the thunderstorm operating procedures. This is the core of what you need to know when you're actually flying near or inside a thunderstorm — these are the actions that keep the aircraft intact and the crew safe. Let's start with the pre-storm area actions, before you even enter the storm. First, if you're using anti-icing or de-icing systems, you must delay activating them until some ice has actually formed. If you turn them on too early, before there's any ice, their effectiveness will be greatly reduced. That's a key point — the ice needs to be there for the system to work properly. Next, in the absence of specific instructions from your manufacturer or operator, you must ensure that ALL anti-icing systems are ON. That includes windscreen heaters. So the sequence is: wait for ice to form, then turn everything on. Now, point viii: disregard any radio navigation indications that are subject to interference from static. The classic example is the ADF — the Automatic Direction Finder. Lightning and static discharge can cause those needles to swing wildly or point to the storm instead of the beacon. Do not follow them. Point ix: turn the cockpit lighting fully ON. Then lower the crew seats and lower the sun visors. Why? To minimise the effect of any lightning flashes. A bright flash in a dark cockpit can temporarily blind you, so you pre-brighten the cockpit and shield your eyes. Point x: follow the manufacturer's or operator's recommendations on the use of the flight director, autopilot, and manometric locks. Manometric locks are the locks that hold your altitude, Mach, rate of climb or descent, and airspeed settings. If those recommendations are not stated, then you should disengage the height lock, Mach lock, rate of climb or descent lock, and airspeed lock. However — and this is important — the yaw damper, if fitted, should remain operative. The yaw damper helps control Dutch roll and keeps the aircraft stable in yaw. Now, here's a nuance: on many aircraft, the autopilot, when engaged in a suitable mode — such as turbulence mode or basic attitude mode — is likely to produce lower structural loads than you would get from manual flight. So the autopilot can actually be your friend in turbulence. But there's a catch: if major trim movements occur due to the autopilot's automatic trim, you should disengage the autopilot. Also note that Mach trim operation may occur on some aircraft, but the Mach trim should remain engaged — do not turn it off. Point xi: continue operating — not just monitoring — the weather radar or other on-board systems. You actively use the radar to select the safest track for penetration, and to minimise the time of exposure while avoiding areas of intense activity. You're not a passive observer; you're actively steering around the worst cells. Point xii: be prepared for turbulence, rain, hail, snow, icing, lightning, static discharge, and windshear. That's the full list of hazards. In turbine-powered aircraft, switch on the continuous ignition system. This reduces the possibility of an engine flame-out due to water ingestion — large amounts of water can snuff out the flame in the combustion chamber. But ensure that limitations on its use, if any, are not exceeded. Also, see AIC 29/2004 — that's an Aeronautical Information Circular about engine malfunction caused by lightning strikes. Point xiii: avoid flying over the top of a thunderstorm whenever possible. Overflying small convective cells close to large storms should also be avoided, particularly if they are on the upwind side of a large storm, because they may grow very quickly. Similarly, do not contemplate flying beneath the cumulonimbus cloud. In addition to the dangers of turbulence, rain, hail, snow, or lightning, there may well be low cloud base, poor visibility, and possibly low-level windshear. Now we move to the storm area — when you are actually inside the thunderstorm. Point i: control the aircraft regardless of all else. That is your number one priority. Nothing else matters if you lose control. Point ii: concentrate on maintaining a constant pitch attitude appropriate to climb, cruise, or descent, by reference to the attitude indicators. Carefully avoid harsh or excessive control movements. Do not be misled by conflicting indications on other instruments. For example, the altimeter may be unreliable due to pressure changes, the airspeed indicator may fluctuate — trust your attitude indicator. Also, do not allow large attitude excursions in the rolling plane to persist, because these may result in nose-down pitch changes. If you let the aircraft roll too far, the nose can drop, and that can lead to a dangerous loss of altitude or even a dive. Point iii: maintain the original heading — it is usually the quickest way out. Do not attempt any turns. Turning in a thunderstorm can expose the aircraft to different forces and may increase structural loads or disorient you. Just hold your heading and fly straight through. That figure shows the formation of rime ice and rain ice — it builds up very quickly, and the pilot's action should be to turn onto a reciprocal heading. But note that this figure is about ice formation, not the storm penetration procedure itself. In the storm, you hold your heading. So to summarise: before the storm, you prepare by turning on anti-icing after ice forms, brightening the cockpit, lowering seats and visors, managing autopilot and locks correctly, actively using radar, and switching on continuous ignition. Inside the storm, you control the aircraft first, maintain a constant pitch attitude by the attitude indicator, avoid harsh inputs, and hold your original heading without turning.