How are planes tested before they are certified for use?

Before a plane can be certified for use, it must undergo a series of rigorous tests to ensure it is safe for passengers and crew. These tests are conducted by regulatory agencies, such as the Federal Aviation Administration (FAA) in the United States, and include both ground and flight testing.

Ground testing involves testing the plane's systems, such as the engines, electrical systems, and hydraulic systems, to ensure they are functioning properly. Flight testing involves taking the plane up into the air and testing its performance under various conditions, such as different altitudes, speeds, and weather conditions.

The testing process also includes testing the plane's ability to handle emergencies, such as engine failures or other malfunctions, to ensure that the crew can safely handle any situation that may arise.

Once all testing has been completed and any necessary modifications have been made, the regulatory agency will review the data and issue a certification if the plane meets all safety requirements. This certification is required before the plane can be put into commercial use.