CFI to CFI
Studying the stall/spin
Spin recovery technique is not all you need to know
Do you think you are a highly proficient pilot who can recover from an accidental stall/spin at pattern altitude? Well, think again: Recovery from such an unfortunate occurrence probably isn't in the cards for you, no matter how good you are.
According to a new AOPA Air Safety Foundation Topic Specific Study (TSS) available on the ASF NTSB accident database page, almost 97 percent of fatal stall/spin accidents occur at or below pattern altitude, mainly because of the lack of time to recover. In a typical light single-engine airplane you'll have between six and 10 seconds to recover from a spin started at pattern altitude, given spin descent rates typically between 5,000 and 8,000 fpm.
Some pilots advocate aerobatic training as a means of avoiding stall/spin accidents, and no doubt aerobatic training can do wonders for both confidence and proficiency. But according to the new ASF study, such training is of little help in avoiding stall/spin crashes when close to the ground, as evidenced by occasional airshow accidents involving very skilled and experienced pilots. The key is to know enough to avoid getting into a stall/spin condition, especially with precious little space between you and the ground.
Consider the plight of a Comanche 250 pilot several years ago. He and his two passengers were anxious to get to Lakeland (Florida) Linder Regional Airport for a week steeped in aviation activity at Sun 'n Fun. Following other airplanes in the pattern, the pilot entered a tight downwind for Runway 9 Left. Witnesses on the ground reported that the Comanche's airspeed seemed slower than that of the other airplanes in the pattern, and it overshot the centerline when turning from base to final. As soon as the airplane turned final it suddenly went into a 90-degree left bank and nosed into the ground. Another classic stall/spin accident.
How did this pilot get himself into this situation? No one knows for sure, but it's a good bet that the sequence of events leading up to the accident went something like this: When the pilot realized he had overshot the runway's extended centerline when turning final, he went into a steep bank to the left and added a lot of left rudder to get the aircraft back to the runway centerline. When he applied excessive left rudder the left wing dropped further, to about a 45-degree angle. At this angle of bank the stall speed increased by at least 10 knots and probably was very near the approach-to-landing speed. He then applied right aileron to arrest the bank, placing the aircraft in an uncoordinated condition. The nose dropped so he pulled back on the yoke to correct the pitch. The airspeed deteriorated further; the airplane stalled and rotated to the left at about 250 feet above the ground. In less than two seconds it was all over and three people were dead.
A pilot's chances of surviving a stall/spin accident are less than the survival rate for many other types of crashes because of the usual low proximity to the ground and the steep angle at which the aircraft strikes the terrain.
One surprising finding of the new ASF study was that 91 percent of the fatal stall/spin "instructional" accidents occurred with an instructor onboard; only 9 percent occurred during student solo. One reason may be that perhaps instructors tend to "push the envelope" and fly the airplane close to its limits during dual instruction.
What can we instructors do to keep our students from falling victim to a stall/spin accident? Concentrate on teaching our students how to avoid conditions where a stall/spin accident is likely to occur, and to be extremely alert when maneuvering close to the ground-such as in the traffic pattern. This is not the time to be distracted by idle conversation, unnecessary radio work, worrying about a rental car, or folding charts.
Make certain that students have a basic understanding of stall/spin aerodynamics. I can recall my primary instructor yelling from the right seat, "Watch your airspeed; don't get too slow or you'll stall the airplane." Maintaining adequate airspeed was about the sum total of my knowledge of stalls at that time. I learned later that there were other elements involved in stalling an airplane aside from low airspeed. Angle of attack (AOA) is a major factor. If you exceed the critical AOA, you will stall, even in a dive. Particularly if the aircraft is not properly coordinated, a spin could result.
A spin is simply the airplane rotating around the vertical axis with unequally stalled wings. The AOA of the descending wing is greater than the AOA of the ascending wing because the angle of the relative wind to each is different. Consequently, the ascending wing is providing more lift than the other; this causes the rotation. This can easily be demonstrated on the ground with a model airplane and the instructor's showing some of the different attitudes in which a stall and a spin can occur. Teach the dangers of the base-to-final overshoot as illustrated in the Lakeland accident.
Teaching the angle-of-attack concept can be difficult during primary training, mostly because a student never sees a stall occur with the nose below the horizon. It is difficult to get students to understand that stalls can occur at any attitude-even in a steep dive-and at any airspeed. This point needs to be driven home.
While teaching stalls to a primary student or executing stalls during a flight review, we expect the aircraft to stall and know that it may try to rotate. We are ready to react with opposite rudder to keep the airplane from spinning, and recovery from the stall or initial stages of a spin is accomplished with little altitude loss. But what if the stall and/or spin comes as a surprise, as it undoubtedly did for the pilot at Lakeland? Add the element of surprise while at or below pattern altitude, and the outcome is usually tragic.
ASF in September is introducing a new safety seminar on maneuvering flight, called "Watch This!" It emphasizes the risks of maneuvering flight, and it is an excellent way to review the hazards of stall/spin accidents and how to prevent them. Have your students attend with you. Check the Web site to find out when the new seminar will be presented in your area.
While waiting for the seminar, check out all of ASF accident database. The Web site is a treasure trove of safety information for both you and your students.
Richard Hiner retired from the AOPA Air Safety Foundation as vice president of training. He can be contacted at [email protected].
By Richard Hiner