Aircraft evolution is really quite fascinating—right up to the Boeing 737 Max 8.
Initially, the Wright Brothers (Wilbur was the real inventor, Orville was the trusty sidekick) actually bent the wings to cause it to turn. Fortunately, if wings are fabric covered wood slats held up by metal cables, bending them is easy. Soon, elevators (the little wings at the tail) controlled whether the aeroplane pointed up or down, and ailerons (movable sections of the main wings) determined whether a plane would angle and turn; the rudder helps turns but is mainly to keep the back of the plane coordinated with the front.
The United States entered World War II in 1941 with most of its aircraft still made of wood frames covered by fabric AND two sets of wings, but more modern planes were arriving and more under development. By 1945, the US Army Air Corps (there was no US Air Force until 1947) was flying multi-engine, high altitude aircraft with pressurized cabins. Next, jet engines replaced many propeller-driven airplanes. Soon passenger aircraft were taking business from the railroads.
The biggest change came when the technology changed from mechanical controls to computers. Small general aviation aircraft, for example, have cables connected from the pilot’s yoke (the thing that looks like a partial steering wheel) and the rudder pedals to the various control surfaces. The pilot pulls back on the yoke and the plane points its nose up; push and the nose goes down. There are other factors that that play a parrt, but you get the idea.
Fly-by-wire describes having a computer between the pilot and the aircraft control surfaces. When the pilot pulls back on the yoke, it is really a computer interface that gives a command to the elevators to move. It’s designed so that to the pilot, it feels the same regardless if it’s mechanical linkages or fly-by-wire. So far, so good.
Basic general aviation planes are built to be stable, and therefore forgiving. The Cessna 172 that I learned to fly, for example, could recover itself from some unusual situations (like a spn) if I just let go of all of the controls. I never tested this, but like most student pilots, I was harder on that little plane than it was on me.
When you add computers, there are all kinds of possibilities, starting with sophisticated autopilots. A military fighter aircraft ideally needs to be highly maneuverable, which means you sacrifice stability. However, by adding a computer, it’s not just the commands from the pilot, but hundreds of little adjustments by the computer. These invisibly make the aircraft act stable but still give the pilot control.
In a modern military aircraft, the pilot is the weak link. The aircraft can accelerate to speeds that would cause the pilot to black out. The aircraft can fly longer than the pilot can remain alert. The pilot’s main job is to provide judgment; even so-called “drones” are remotely piloted.
Planes like the Boeing 737 Max 8 have an upgraded computer system. The new 737 seemed so similar to previous versions, except for the computer and software, that the Federal Aviation Administration didn’t require the exhaustive testing required of a brand new aircraft. It’s possible that the new software has some flaws, flaws that reportedly cause the plane’s nose to drop and not respond when the pilot pulls the yoke back to correct it.
This is only a guess, based on various news reports. When a thorough investigation is complete, including reviewing the data from the flight recorders—the “black boxes”—then we should know more.