Stalling — Page 191, Lesson 230

Let's pick up with the special phenomena of the stall. We've covered the basic 1g stall, where the wing reaches its critical angle of attack in steady, level flight. Now I want to walk you through the situations where the stall gets complicated — where it happens unexpectedly, violently, or during recovery. First, the crossed-control stall. This one occurs when you're flying at a high angle of attack and you apply rudder in the opposite direction to the aileron, or too much rudder in the same direction as the aileron. Think about what that does: you're asking the aircraft to do two conflicting things at once. The tell-tale sign is the ball in the slip indicator being displaced from neutral — that's your instrument telling you the aircraft is no longer in balanced, co-ordinated flight. Here's the dangerous part: crossed-control stalls can occur with little or no warning. One wing will stall a long time before the other, and you can get a quite violent wing drop. Now, the instinctive reaction when the wing drops is to pick it up with aileron — you must resist that. The correct action is to use the rudder to keep the aircraft in balanced, co-ordinated flight at all times, ball in the middle. And this is especially critical at low airspeeds and high angles of attack, where you have little margin. Next, the accelerated stall. This is caused by abrupt or excessive control movement. It can occur during a sudden change in the flight path — for example, during manoeuvres such as steep turns or a rapid recovery from a dive. It's called "accelerated" because it occurs at a load factor greater than 1g. That's the key distinction: in a normal stall you're at 1g, but here the aircraft is pulling more than its own weight in load. Because of that, an accelerated stall is usually more violent than a 1g stall, and it's often unexpected because the airspeed is relatively high. The pilot sees a high speed and assumes there's no stall risk — but the high load factor raises the stall speed, so the wing can stall at an airspeed that looks perfectly safe. Then we have the secondary stall. This one is triggered while you're attempting to recover from a stall. It usually happens because you try to hasten the recovery — either by not decreasing the angle of attack enough at stall warning, or by not allowing sufficient time for the aircraft to begin flying again before attempting to regain lost altitude. The correct technique, with full power still applied, is to relax the back pressure and allow the aeroplane to fly before reapplying moderate back pressure to regain lost height. In other words, don't rush it — let the wing start flying again first. Now, a word on large aircraft. During airline "type" conversion training on large aircraft, full stalls are not practised. To familiarize pilots with the characteristics of their aircraft, only the approach to stall is carried out — that's the stick shaker activation, the warning that precedes the actual stall. And for jet aircraft with swept wings, there are no special considerations during the approach to the stall. That's the end of this section — the swept-wing jet behaves predictably right up to the warning.