“…a North American SNJ-5 airplane impacted terrain following a loss of control during initial climb after take-off from runway 13R (8,000 ft. by 200 ft.) at Kingsville Naval Air Station (NQI), Kingsville, Texas. The pilot and pilot rated passenger were fatally injured and the airplane was destroyed. Visual meteorological conditions prevailed.
Witnesses reported that the airplane took off on runway 13R and had requested a right-hand teardrop turn for a departure toward the north. The witnesses reported seeing the airplane in a steep right bank with some witnesses reporting that the bank angle exceeded 90 degrees. The airplane descended nose low and the right bank angle lessened before the airplane struck the ground”.
Stalls and spins get the lion’s share of coverage in instruction and in article and videos concerning Loss of Control – Inflight (LOC-I). To be sure, stall/spin events are hazards requiring this focus—the record shows that LOC-I events are the most common fatal accident scenario, and most LOC-I events appear to be stalls that often develop into a spin before impact.
There is another LOC-I sequencethat is neither a stall nor a spin. It is a natural outcome of aircraft stability, and a characteristic of all longitudinally (pitch) stable airplanes. Yet it is not mentioned by name, trained, or evaluated for or in the Practical Tests for pilot certificates or ratings. The sequence is a spiral dive, and it’s what witnesses in the SNJ crash seem to describe.
Here’s how the U.S. Airplane Flying Handbook explains a spiral:
Stability, steep turns and spirals
Put another way, a pitch-stable airplane will seek the indicated airspeed (actually, angle of attack) for which it is trimmed. The G load on the airplane will increase only if the pilot resists the airplane’s natural tendency to change pitch if it gets off its trimmed speed. An airplane will not stall on its own. The pilot has to actively pull against the airplane’s stability to make it stall.
Many aircraft are stability-neutral or even slightly unstable in roll. Enter a shallow bank and the airplane may remain banked or slowly return to approximately wings-level flight. But bank steeply enough and most aircraft will not leveltheir own wings. In fact, in a steep turn most airplanes will continue to bank progressively more steeply. This is sometimes called the overbanking tendency, the reason it may take opposite aileron input to maintain bank once established in a steep turn.
You’ve probably seen graphs and diagrams that show the relationship between bank angle and stalling speed. What’s not often well-explained is that this relationshipis only valid in level, coordinated flight. If the pilot does not resist the airplane’s tendencies and its nose drops to seek the trimmed airspeed, the G load does not increase; it increases some if the pilot applies some but not enoughresistance to maintain level flight.
What happensif the airplane enters a steep turn and the pilot provides more or less resistance than is necessary to maintain level flight? We’ll use the 60° bank example simply because we can speak in whole numbers:
- If the pilot adds more than 2Gof resistance, the airplane will climb; and, if there is sufficient power, the airplane will enter a sustained climb. With insufficient power the wing will quickly enter an accelerated stall.
- If the pilot applies exactly 2Gof 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, seeking to attain and maintain the trimmed airspeed.
- If the pilot does not apply at least 2Gof resistance with elevator, power or both, the airplane will descend, seeking to attain and maintain the trimmed airspeed.
One of five outcomes results:
- The pilot recovers from the spiral using the recovery technique described earlier.
- The airplane spirals rapidly into terrain.
- The airplane is high enough at the entry into the spiral that it has time to accelerate beyond VNE before it impacts terrain. Exceeding structural load limits causes the airplane to break up in flight.
- The pilot does not recognize the spiral for what it is, or does not know the proper recovery technique, or panics. She/he pulls back on the controls, perhaps instinctively. The G load builds and over-stresses the airframe; the airplane breaks up in flight.
- The pilot attempts a recovery but does not apply forward control pressure to unload the wing. The airplane exceeds structural limits in the pull-out and breaks up in flight.
Frankly, I think more airplanes impact the ground out of spirals entered from uncorrected steep banks in the traffic pattern, that is, the pilot not doing enough because of distraction and letting the airplane do what it wants, than crash from stall/spin mishaps resulting from the pilot doing too much, i.e., resisting the airplane’s tendencies and intervening (albeit incorrectly).
So, if a pilot plans such a departure, what does that pilot need to be thinking about?
- “If I am going to bank 45° while climbing I will need to exceed 1.4G in the climb or the airplane will descend into a spiral entry.”
- “If I am going to bank 60° I will need to exceed 2G in the climb or the airplane will descend into a spiral entry.”
- “I should not exceed 60° bank in the climb because the G load required will increase exponentially and the airplane will either stall or slide into a spiral entry.”
- “If at any point the airplane begins to descend all I need to do to recover is to reduce the bank angle and unload the wing.”
- “Is this even a good idea at all? What are my margins, and is there any real benefit from the added risk?”