It’s early on in your academic training these days when a teacher refers to the GIGO principle. Simply stated, if you are using a computer, it doesn’t matter how great the machine or the program is if you input bad data. If you put in garbage, it will give you garbage results. Garbage in, garbage out: GIGO.
In flying this is a very real concern, particularly when it comes to programming a GPS. It’s one thing if you inadvertently put in a wrong fix that’s close to the right one, but that’s rare. What’s more likely to happen is that you put in the wrong fix or the wrong piece of performance information, only to suddenly find yourself asking what is going on. When the airplane makes a turn you aren’t expecting, you’ll be scrambling to figure out where the mistake is. It’s great if it happens on the next fix. That usually becomes readily apparent. It’s not so great if you programmed in the wrong fix several legs down the road.
This is an easy mistake to make on a GPS that is programmed with a knob, and it’s an easy mistake to make in a crew environment. I’ll give you an example: I was in a simulator event, and I had the airplane doing exactly what I wanted it to do. Trying to stay ahead of things, I decided to program the climb performance, not registering that the performance I was asking for was for the cruise climb. Asking the airplane to change its profile would cause all kinds of problems on the departure procedure. Following our prescribed procedure, I asked the captain to verify what I was getting ready to do. He did. I hit the button and executed the new plan. To my horror, the airplane began to accelerate and climb like it had a date with Mars.
I quickly turned off the autopilot and autothrottles, and I asked the captain to reprogram “the box” while I hand-flew and kept us out of further trouble. In my peripheral vision, I saw the instructor smile and write furiously. In the debrief, we got kudos for catching the problem immediately and fixing it, but we also got a reminder that GIGO can happen at any time, at any place. It was a great lesson, and it happened in the sim, where nobody could get hurt.
I’ve flown now for more than 20 years, and I have a litany of such GIGO examples—some mundane, some not so much. What I can say is that I don’t tend to make the same mistake twice, but I’ve learned that I am never going to be immune to this kind of error, which is good, as it keeps me on my toes.
But if you want to see how catastrophic GIGO can be, just look at the report for American Airlines Flight 965, which crashed into a mountain in Colombia in 1995 because of a flight management system programming error. It’s a stark reminder of how quickly things can go wrong, even for an experienced crew.—Chip Wright