What caused the crash of Flight 3407?

Sadly, the two pilots who flew it never can tell us — even if they knew, which they may not have because everything appears to have happened at lightning speed.

The National Transportation Safety Board eventually will determine the most likely causes and scenario. It already is doing an excellent job of piecing together the facts and of informing the public — a daunting dual task, requiring delicate balancing of many considerations.

I can only speculate. I was a captain with what is now know as US Airways. I have more than 11,000 hours in the air, and am type-rated in the similarly configured FH227 high wing turboprop airliner.

In fact, that’s the aircraft I flew on the very last airline flight into Olean back in the 1970s.

Here’s what we know about Flight 3407. There was clearly no forward motion after impact. But — how can that be, when planes fly so fast?

The force that keeps airplanes up is called lift — air pressure under the wing. When the force of the air pressure under the wing exceeds the weight of the airplane, it flys. When that lift is lost it stops flying — or “stalls.”

Weight increases the amount of lift (and speed) needed to fly. As the speed increases so does the amount of lift — and visa versa.

Ice—which disrupts the airflow over the wing — reduces lift, adds weight and increases the stall speed.

When both wings have equal lift the result is level flight. Forward speed through the air is the key. If the airplane gets too slow, one or both of the wings will stall. If both wings stall at the same time, the nose drops but the airplane continues straight ahead.

However, if only one wing stalls, the airplane rolls steeply and turns abruptly towards the stalled wing. With one wing “flying” and the other not, the airplane makes very rapid turns, looses all forward motion and descends just about vertically at an extremely high rate.

This is called a “spin” — which is the most dangerous maneuver an airplane can experience when close to the ground.

Since the 1950s, pilots have not been required to learn spins to get their license. Spins are very violent maneuvers—and if a pilot is not trained in them it can be disastrous.

I can personally attest to that. When I was in the Air Force I accidentally got into a spin while flying a light trainer.

The procedure to recover from a spin is to push the controls forward to build up sufficient speed to stop the spin. But the natural tendency is to do the opposite and pull the controls back to stay away from the fast approaching earth.

Not having prior spin training, that’s exactly what I did — and I held the controls back keeping me in that spin right to the ground, resulting in a crash with no forward motion after impact. That’s similar to the impact conditions of Flight 3407.

Much later I trained in spin recovery and discovered how absolutely frightening and disruptive spins can be until you learn how to fly out of them.

All Airline Transport Pilots are trained in stalls—but not in spins. So, what happens if the unexpected occurs, as it appears to have with Flight 3407? And how did they get to that point?

We know there was icing and that their plane had deicing boots that were turned on. But even if the boots were working OK, ice also builds up on other areas, adding considerable weight — which affects the plane’s balance — and increases stall speed.

There also is another factor — autopilots.

Autopilots reduce pilot fatigue, and fly the airplane more accurately and precisely than pilots. However, they are also a double-edged sword. An autopilot can make powerful control inputs that the pilot has no awareness of until he turns the autopilot off. As a case in point, a number of years ago on a BAC 111 jet airliner flight to Chicago we had minor wing fuel tank imbalances, causing the airplane to bank slightly towards the heavier wing. So we started adjusted the imbalance by feeding both engines from the heavier tank.

But we then got distracted and left the cross-feed on too long, causing an even larger opposite imbalance — which we didn’t notice until we switched off the autopilot prior to our decent from altitude.

Unbeknownst to us, the autopilot had kept applying more and more counteracting roll control pressure as one wing got lighter. When we switched off the autopilot, all that control pressure was also suddenly released — and in the blink of an eye the airplane abruptly rolled strongly towards the heavy wing.

Luckily we were very high up and going about 550 miles an hour, so we simply manually leveled the wings and rebalanced the fuel load before landing. But what if we’d been in the same place as Flight 3407?

You just can’t “feel” the airplane when the autopilot is on. That’s why many airline pilots I knew did not usually make approaches using the autopilot. That’s also why it’s always a good idea to turn the autopilot off occasionally during flight, just to see what inputs it’s making to the controls as it compensates for changing conditions. Otherwise, if those inputs are large, and the auto pilot should suddenly kick off, it could instantly put the aircraft in a bad position.

In the case of Flight 3407 the autopilot may have been making just such strong control inputs unbeknownst to the pilots. In addition, apparently due to all that icing weight and disturbed lift, they were very close to a stall.

Then, evidently, a safety feature on the autopilot automatically disengaged it. At that moment things happened lightning fast — and either the airplane pitched severely up because of no longer having strong downward control input from the autopilot, or it momentarily pitched down due to the “stick pusher” engaging automatically because the airplane was too close to a stall. Perhaps the pilot, caught off guard, over-corrected and pulled up too hard.

In any case, the airplane evidently entered into a stall, and spin — rolling severely first to the left and then even more severely to the right, changing its direction by 180 degrees—and, within seconds, descending in an almost a flat attitude all the way to the ground.

We may never know exactly what happened for sure. And like all aircraft accidents, it took several things, in a fateful combination, to cause it.

Jack Liguori is a former airline pilot with turboprop ratings.