Low-altitude spins are one of the leading causes of fatal accidents in aviation. While base-to-final stalls get a lot of attention, statistically, the most frequent low-altitude stall/spin happens just after takeoff. Takeoff stalls occur more often but tend to be less deadly than landing stalls. Still, takeoff stalls deserve just as much attention because the risks are significant.

As for your original question, the most dangerous situation, assuming no system failures, depends on the type of aircraft. In swept-wing aircraft, exceeding critical Mach speed at high altitude can lead to Mach tuck, a dangerous nose-down pitch that’s very hard to recover from without plenty of altitude. Low-speed upsets in swept-wing aircraft are also a big concern because recovery often requires thousands of feet, so altitude is your best friend.

In straight-wing aircraft, the risks come from both high-speed and low-speed upsets. Spins in straight-wing aircraft are actually pretty easy to recover from if the pilot is trained and the airplane is working properly. The real danger is altitude. If a spin happens below 500 feet AGL, even a perfect recovery probably won’t leave enough time to avoid a crash.

Spins are often misunderstood as being hard to recover from, but that’s mostly a myth perpetuated by Hollywood and general confusion about stalls and spins. Fatalities from stall/spin accidents are usually because of low altitude and lack of training. Flat spins, for example, are rare and don’t happen on their own. They’re typically caused by spinning with high engine power, which flattens the spin by raising the nose. The real danger of flat spins (and any spin) is running out of altitude before recovery. Reducing power is the key to getting out of a flat spin.

A tail-low spin doesn’t really happen naturally either. Planes are like lawn darts—they naturally want to fall nose-first. If you throw a dart backward, it might tumble for a second, but it’ll eventually stabilize nose-down. Airplanes behave the same way. Airshow maneuvers like tail slides or tail-low hovers might look like tail-low spins, but they’re actually controlled balancing acts by the pilot. The moment those balancing inputs stop, the plane will pitch nose-down like it’s supposed to.

Another dangerous situation is the graveyard spiral. If the bank angle exceeds about 30 degrees, the plane’s natural over-banking tendency can make the bank keep steepening. Without corrective input, the nose drops as the vertical lift decreases, causing airspeed to climb and the spiral to tighten. This cycle continues until the plane either hits the ground or exceeds structural limits. Unlike spins, spirals won’t recover on their own. Most light aircraft will naturally recover from a spin if you release the controls and reduce power, but a spiral requires the pilot to step in and stop it.

Unexpected weather encounters are another thing worth mentioning. Icing or storms can cause major problems, but usually it’s the in-flight upset caused by the weather that leads to an accident. A common example is a VFR pilot flying into IMC. Disorientation sets in, proper bank and attitude aren’t maintained, and the plane enters an over-banking condition. The spiral begins, and the cycle I described earlier takes over. Sometimes, after losing a lot of altitude, the plane exits the clouds, the pilot sees the ground, and they yank the wings level. By then, the airspeed is so high that the sudden change in lift vector from horizontal (in the spiral) to vertical puts a massive aerodynamic load on the plane. This often causes an in-flight breakup—and I’m not talking about your girlfriend.

This is a great topic, and I might actually make a stand-alone post about in-flight upsets and proper recovery techniques. Go out and get some UPRT, and you’ll understand these scenarios a lot better.