What makes an airplane crash?

Human Error/Pilot Error is the leading cause of airplane crashes. The airplane itself is inherently safe and well-constructed, but human beings can and do make mistakes. There have been cases of a part or feature not having been designed well and causing a problem down the road. One memorable example was the cargo door on the DC-10, which opened outward instead of inward and was prone to blowing out at altitude if not secured properly. However that plane doesn't even fly with major carriers anymore and the problem was rectified decades ago. In fact, most of the aircraft with major North American airlines have been flying, in one form or another, for many decades and have had major design flaws corrected, plus the technology available when designing new aircraft has never been better. Plus aircraft undergo extensive computer and real-world testing before a fare-paying passenger ever sets foot in it. As far as "running out of gas", aircraft always take on more fuel than needed for a flight in case there are weather delays in landing or the plane needs to divert to an alternate airport. For example, on a flight from Toronto to Edmonton, the plane will have enough fuel to go to Vancouver, another 1.5 hours away. The only documented cases of this ever happening - and I can only think of 4 out of however many billions of flights haveoccurredd - one was a miscalculation converting to metric, one was due to a hijacking, one was due to the crew not informing the control tower when they were running low on fuel while waiting to land, the only other one was due to a fuel leak (plane landed without incident). Conclusion, it's very unlikely. Planes are built and crews are trained around the idea of redundancy, as in they build in several solutions to one potential problem so if one solution fails then there is a back-up plan, and a back-up to the back-up plan, etc. For example on a two-man crew, the pilot and co-pilot never eat their meal at the same time, and they also don't eat the same thing, just in the off-chance that the "Chicken Supreme" was undercooked. Aircraft technology systems are the same, with several computers monitoring different functions and overlapping each other. In the event of an emergency, pilots are trained to know where their alternate airports are at all time. Just like it's instinct for you to pull over to the shoulder when you get a flat tire or you overheat, pilotsinstinctualy know to head for Airport Z if they're 25% of the way between A and B. So the chances of having to crash land are slim too. In EXTREMELY rare cases, a pilot may have to "ditch", as in land between airports. The reason the plane "crashes" is that due to the extreme weight and physics involved, a plane needs a perfectly level and smooth service to land one, which is why runways are meticulously planned and maintained. It takes great precision to land the aircraft smoothly even on the best of surfaces like these, so landing on something like a field with imperfections can mean the slightest bump or dip can throw the center of gravity off and cause a crash. Still, the chances of ever getting to this point are millions to one. When crashes and incidents do occur, and although rare they do happen, they are thoroughly investigated by the airlines involved and multiple government agencies. The airline industry is incredibly resilient and learns from its mistakes. In fact, many of the safety systems we take for granted today have come out of tragedies decades past. Like the advent of floor-level lighting to guide people towards exits. Essentially, with every year that passes, airplane travel becomes safer and safer.