And be able to take off, no problem, even if one engine quits just as the aircraft is lifting off the runway. And land safely even if one engine quits when the aircraft is as far as it can be from any airport. Aerospace engineers think about everything that can possibly go wrong, and many things beyond that. And then they worry, and plan, and check their calculations, and talk to other people about how to improve their estimates and calculation procedures. They develop simulators to test out every eventuality.
Nothing is left to chance.
Structure Strength of each part, material, weight reduction, life prediction. Break this down into steps involved in manufacturing. Life-cycle cost Minimize cost of owning the vehicle over its entire lifetime. Refine the weight and the design. Flight Simulation Describe the vehicle using mathematics.