Thunderstorms — Page 260, Lesson 218

I want to walk you through the final operational considerations for thunderstorms, starting with take-off and landing problems. When you're close to the ground during take-off, initial climb, final approach, or landing, the aircraft's proximity to the ground makes maintaining a safe flight path very difficult if a thunderstorm is nearby. Some operators give advice on airspeed adjustments to compensate for windshear or turbulence — they may recommend a speed increase of up to 20 knots, depending on the type of aircraft and the degree of turbulence. But the best advice I can give you is this: if there are thunderstorms over or near the aerodrome, delay take-off entirely. If you're approaching to land, hold in an unaffected area or divert to a suitable alternate. For further relevant information, you can refer to AIC 84/2008, also known as Pink 150, titled 'Low Altitude Windshear'. Now let's look at airworthiness and maintenance considerations. Severe weather conditions may cause damage to the aircraft and power plant installations, and some of that damage may be invisible to the naked eye. Flight Manuals and Maintenance documents may quantify levels of turbulence that would trigger a maintenance inspection — similar to the inspections that may be applicable after 'heavy landings'. Hail and lightning damage may often be obvious to crews, but there will be occasions where damage is restricted to parts of the airframe not normally visible from the ground or from the cockpit immediately following a thunderstorm encounter. So here's the critical procedure: if you believe that the aircraft has been exposed to hail, lightning, turbulence greater than 'moderate', or a heavy landing, you must record the fact in the technical log on arrival. That ensures an appropriate inspection is completed before the aircraft is released to service again. Operators should ensure that procedures in their operations manuals for flight crews and maintenance personnel reflect this advice. For light aircraft operators specifically, you should ensure that your aircraft are adequately secured on the ground when severe thunderstorm activity is forecast. Now I want to give you the concluding remarks — these are the hard rules to live by. First: do not take off if a thunderstorm is overhead or approaching. Second: at destination, hold clear if a thunderstorm is overhead or approaching — divert if necessary. Third: avoid severe thunderstorms even at the cost of diversion or an intermediate landing. If avoidance is impossible, follow the procedures recommended in the flight or operations manual or in this circular. Fourth: pilots of turbo-jet swept-wing transport aircraft should ensure they are fully conversant with the control problems that may be met in turbulence with the type of aircraft they fly. And finally: after an encounter with a thunderstorm, consider reporting the event in the aircraft technical log — this will ensure a full and proper investigation of the aircraft occurs.