Aviation, at least in the US, has a surprisingly short list of rules. Part 91 of the federal transportation and other things regulations applies to everyone who flies anything. And as I told students, there is a lot of implied good judgement in the rules. Legal isn’t always smart. Smart comes down to the most important rule in the book: The pilot-in-command has the final authority and responsibility for the flight. The pilot in command can deviate from any of the rules if in his judgement safety demands it. Yes, you will have to explain, especially if something gets bent or broken. But the PIC is the boss, and everything else is based on trying to keep flying things out of undue proximity to the ground and to each other.
If you can’t see the ground, and you don’t have a “fly in clouds” license, don’t fly in the clouds. If you have not recently practiced flying and landing at night, don’t fly at night. If you are going eastbound, more of less, fly at an odd thousand feet plus 500 (if you are visual flight rules). Westbound gets the even thousands, plus 500. Don’t fly so close to the ground that you fly into the ground. Don’t be stupid. Don’t fly a broken airplane unless you label the broken thing so that you don’t get fooled and start to trust it. When around an airport, look out for other planes. The slowest, least-maneuverable thing has the right of way. Emergencies have the right of way (i.e. the guy on fire can land ahead of a blimp.)
If you are an airliner, you can’t go sightseeing off the approved route. Why? Because in 1956 two airliners were doing that, over the Grand Canyon, and one descended onto the other. People died. If your airplane is not certified and equipped for flying in known icing, don’t fly into known icing. Why? Because people did, and crashed, and died. Unless you are cleared for take off, or to cross the runway, and you and the controller agree that there is no one else on the runway, don’t take off, or don’t cross the runway. Why? March 1977, KLM and Pan Am 747s collided on the main runway at Tenerife, Canary Islands, killing 583 people. It also showed that better cockpit communication rules might be needed, because the KLM captain did not listen to his copilot/First Officer when the man asked about the Pan Am being clear of the runway. It wasn’t.
Engineering has its own rules. You can’t build certain things certain ways. You can’t build a 2000 foot-tall radio antenna without guy-wires and other supports. Dams need to be anchored to the bedrock beside them with a watertight seal (see Teton Dam, 1976). You have to allow for resonances in bridges where the wind blows (Tacoma Narrows). There are times where heavy structure trumps airy design.
Lots of areas of endeavor have rules written in blood. I’m not going to go into recent events in New Mexico, other than to say that I feel very, very sorry for the families of the woman who was killed and the man who was injured. Had the Four Rules of firearms handling been applied, it is possible that the accident would not have happened. 1. The firearm is always loaded. 2. Do not touch the trigger until you are ready to fire. 3. Do not point the firearm at anything you are not willing to destroy. 4. Remember what is behind your target. Heck, Fr. Martial smiled when he observed that when I stopped cleaning the desks in order to talk to him, I moved my finger off the “trigger” of the spray bottle and pointed the bottle at the outside wall. (Spraying one’s boss with cleaner/disinfectant is generally considered somewhat gauche.)
“Why can’t I skim the bottom of the clouds? It’s fun!” It’s fun until the clouds get lower, or someone else appears on an instrument flight plan and descends on top of you, or you don’t see a mountain in time.
“Why can’t I stay at 6500′ MSL* until it’s time to climb to get through the pass into Albuquerque?” Because there is a 7200′ ridge in the way. It loves to eat airplanes. For a while it was averaging one a year. Beware of clouds with crunchy middles.
*Mean Sea Level. Then there’s ASL, above sea level. The two are generally, but not always, the same. The most important, however, is AGL. Above ground level, where one should remain between takeoff and landing.