Human factors - I love this stuff. The John Denver crash is a perfect example of this. Something that looks fine and dandy while you are standing on the tarmac becomes a nightmare when airborne.
I’ll share two personal human factors stories - one bad, one good.
The bad one is from an older airplane, the venerable 727. I sat sideways on that thing flying the panel for 18 months, and I can assure you that human factors never trickled down to the 727 FE panel. It was obvious that every system (fuel, hydraulics, electrics, pneumatics, etc) was designed by a different person. On one system (fuel) an illuminated light indicated that something was NOT working (ie a boost pump). On a different system (anti-ice) an illuminated light meant that the system WAS working. And for fuel crossfeed, the light FLASHED ONCE after you activated the switch. Before and after activation it was not illuminated. Multi-position switches also were not consistent. For fuel, a normal flow had all knobs vertical. For electrics, a normal flow had all knobs horizontal. In addition, every system used one of three colors of lights in a different way - an illuminated blue light was good for anti-ice, but bad for fuel. Overall, a human factors nightmare. The only way to overcome it was repitition, repitition and more repitition in the simulator. And even after that guys still screwed things up. If you promise not to sue, I’ll tell you the story of one poor soul:
Fresh out of training and flying the line, he forgot to turn on ANY fuel boost pumps on taxi-out. Not a problem while taxiing and while flying at lower altitudes, because the engines can suction-feed the fuel. As the 727 climbed, he never noticed that the boost pumps were off. Passing 30,000 feet everyone figured it out as all three engines flamed out due to fuel starvation! :eek:
Now for the good. On newer airplanes, and even older ones that we acquire from other airlines, some human factors lessons are applied. For example, on the MD-80s every switch on the overhead panel has it’s “ON” position as forward. In this case “forward” means the same direction you push the throttles to accelerate. So no matter what system you are reaching for, to turn it on you move the switch forward. To turn it off, move it backward. Same thing on the forward console panels - up is on, down is off. Always. Some airplanes came to us with different switchology, but they were modified to our standard before they came on the line. Consistency like this is a VERY good thing, because you do not have to think about which way to throw any switch to get the desired effect.
Human factors design in airplanes is a constantly evolving process. Airplanes made today have learned many lessons from the past - gear handles are shaped like a small wheel, flap handles look like a flap, etc. But the new problems are occuring where advances are being made - namely automation. The phrase “why is it doing that?” has been uttered countless times in simulators and aircraft across the globe. Different philosophies about automation (the most notable being between Airbus and Boeing) result in vastly different methods for accomplishing the same task. The current strive for common automation practices is similar to past battles fought for common mechanical practices. Lessons will be learned (often in blood), and a standard will eventually appear.
Of course these standards would never be required for a homebuilt like the Long-EZ, but you always hope that people are learning SOMETHING from other people’s mistakes.