In terms of total operational life and maintenance cycles, airplanes last significantly longer than cars. A typical commercial airliner, like a Boeing 737 or Airbus A320, is designed to remain in active service for 20 to 30 years, often logging over 60,000 to 100,000 flight hours. In contrast, the average lifespan of a modern car is approximately 12 years or 200,000 miles. The reason for this longevity is "preventative maintenance"; while a car is often driven until something breaks, an airplane undergoes rigorous, legally mandated "checks" (A, B, C, and D checks) where the aircraft is virtually taken apart and rebuilt to "zero-time" standards multiple times during its life. An engine on a plane is often replaced or overhauled several times before the airframe itself is retired. However, airplanes have a "life limit" based on pressurization cycles—the literal expanding and contracting of the fuselage—which eventually causes "metal fatigue" that cannot be safely repaired. Once an airframe reaches its cycle limit, it is retired to a "boneyard," even if its engines and avionics are still in perfect working order.