Precision and non-precision approaches are two different types of instrument approaches used in aviation to guide an aircraft from the enroute phase of flight to the landing phase.
A precision approach is an instrument approach that provides accurate and precise guidance to an aircraft to align with and land on a specific runway. The most common type of precision approach is the Instrument Landing System (ILS), which provides lateral and vertical guidance to the aircraft by transmitting radio signals to the onboard receiver. The ILS allows the aircraft to descend to a very low altitude above the runway and make a landing under low visibility conditions.
A non-precision approach is an instrument approach that provides lateral guidance to the aircraft but not vertical guidance. Non-precision approaches are generally used in situations where the airport is not equipped with an ILS or the aircraft is not equipped with the necessary equipment to receive ILS signals. Examples of non-precision approaches include the VOR (Very High Frequency Omnidirectional Range) approach and the NDB (Non-Directional Beacon) approach. In non-precision approaches, the aircraft typically descends to a minimum altitude at a predetermined point along the approach path, and from there the pilot must visually acquire the runway environment and land the aircraft.
While precision approaches are more accurate and provide greater landing capabilities in low visibility conditions, they require more sophisticated equipment and are often more complex to execute. Non-precision approaches are less accurate and less capable of landing under low visibility conditions but are simpler to execute and require less sophisticated equipment.
Both precision and non-precision approaches are critical in aviation and are used to guide aircraft safely from the enroute phase to the landing phase of flight.