What is the hardest pilot certificate to get?

The hardest pilot certificate to get is generally considered to be the Airline Transport Pilot certificate, ATP, which is the highest level of pilot certification, or the Certified Flight Instructor certificate with instrument rating for difficulty of checkride. The ATP requires 1500 hours flight time, extensive knowledge of advanced aerodynamics, jet systems, crew resource management, and passing very difficult written and practical tests including ATP-CTP course, and is required to be captain for airlines. Many pilots consider Certified Flight Instructor, CFI, checkride hardest because you must not only fly perfectly but teach while flying and demonstrate deep understanding of all fundamentals, with high failure rate around 40 percent. Other difficult certificates include seaplane rating for challenging water handling, and helicopter ATP. For instrument flying, the hardest approach to get certified for is CAT III approach which requires special training and equipment. Overall, ATP is hardest due to time, cost, and knowledge required, taking years to build 1500 hours. In military, test pilot school is even harder. The difficulty also depends on individual, some find instrument rating hardest due to precision flying in clouds. All pilot certificates require medical, written exam, and checkride with FAA examiner, and hardest is one that demands most experience and theoretical knowledge, which is ATP, often called PhD of aviation, requiring thousands of dollars and years of commitment.