Page 24 - August18T

climb. With insufficient power the wing will quickly enter an accelerated stall.
• If the pilot applies exactly 2G of resistance, the airplane remains level. Airspeed will decrease from the drag of high angle of attack flight, so the pilot will have to add power to maintain airspeed. If airspeed increases, the airplane will climb or the pilot may reduce back pressure – more power means the same G load is sustained at a lower angle of attack. If airspeed decreases, the airplane will descend and its nose will drop below the horizon seeking to attain and maintain the trimmed airspeed.
• If the pilot does not apply at least 2G of resistance with eleva- tor, power or both, the airplane will descend. Its nose will drop below the horizon, seeking to attain and maintain the trimmed airspeed.
Further complicating this situation is the overbanking ten- dency. Unless the pilot corrects for it, once in a steep turn, the wing will continue to bank further. This means the nose will drop even more. The airplane, now sensing more air- speed than that for which it is trimmed, will naturally pitch upward to return to the slower, trimmed speed. Except this pitch change is “up” relative to the airframe, not relative to the horizon. In a steep (and getting steeper) turn, this just tightens the downward spiral, increasing airspeed even more. Airspeed and vertical speed increase incredibly fast. As bank angle and speed increase, G load increases to (and eventually beyond) the airplane’s structural limit.
Spirals
Put simply, a spiral is a steep turn that the pilot allows to go bad. Once in a spiral, one of five outcomes results:
1. The pilot recovers from the spiral using the recovery technique described earlier.
2. The airplane spirals rapidly into terrain.
3. Theairplaneishighenoughattheentryintothespiralthat it has time to accelerate beyond VNE before it impacts ter- rain. Exceeding structural load limits causes the airplane to break up in flight.
4. Thepilotdoesnotrecognizethespiralforwhatitis,ordoes not know the proper recovery technique, or panics. She/he pulls back on the controls, perhaps instinctively. The G load builds and overstresses the airframe; the airplane breaks up in flight.
5. The pilot attempts a recovery but does not apply forward control pressure to unload the wing. The airplane exceeds structural limits in the pullout and breaks up in flight.
Those sequences may sound familiar. The outcome of at-
tempted visual flight in Instrument Meteorological Conditions (“VFR into IMC”) follows one of these patterns. The same goes for a thunderstorm or other strong turbulence encounter, even for an instrument pilot. An airplane’s natural spiral tendency helps explain the hazards of the visual portion of an IFR circle-to- land approach, and to landing at a “dark hole” airport at night. In both of these situations, visibility is reduced; the pilot is usually focused on the runway trying to keep it in sight and unusual visual cues tempt the pilot into flying steep banks close to the ground. Frankly, I think more airplanes impact the ground out of spirals entered from uncorrected steep banks in the traffic pattern than they do from stalls.
Training from this Trainer
Let’s go back to our example. The SNJ pilot clearly intended to make a right-turning departure; he asked for permission to do so. I interpret a “right hand teardrop turn” from Runway 13 for a departure to the north to mean a tight turn to overfly the airfield, as contrasting from a more conventional left turn on course after departure. An airshow-type, Navy-historical air- plane departing from an air show at a Naval Air Station in this “look at me” departure path at least suggests the pilot intended to make a fairly steep turn shortly after lifting off, a turn that could quickly degrade into a spiral. It’s at least consistent with what I see at air shows all the time.
We don’t know yet if there was an engine issue, or t•he pilot pulled into an accelerated stall, or if there was some sort of control issue, or whether there were medical or other issues that led to the flight path that witnesses described. But whether a spiral was a factor in the SNJ crash or not, hopefully you now know a little more about spirals and how to avoid them. T&T
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Thomas P. Turner is an ATP CFII/MEI, holds a master's Degree in Aviation Safety, and was the 2010 National FAA Safety Team Representative of the Year. Subscribe to Tom’s free FLYING LESSONS Weekly e-newsletter at www.mastery-flight-training.com.
22 • TWIN & TURBINE
August 2018