Continuous descent approach
Continuous descent approach (CDA) or optimized profile descent (OPD) is a method by which aircraft approach airports prior to landing. It is designed to reduce fuel consumption and noise compared to certain conventional descents. Instead of approaching an airport in a stairstep fashion, throttling down and requesting permission to descend to each new (lower) altitude, CDA allows for a smooth, constant-angle descent to landing.
A continuous descent approach starts ideally from the top of descent, i.e. at cruise altitude, and allows the aircraft flying its individual optimal vertical profile down to runway threshold. Some airports apply constraints to this individual optimal profile.
Due to the negative association with the term CDA, new procedures introduced at LAX and other US airport are instead called Optimized Profile Descent (OPD). Although CDA procedures were documented at Louisville airport, the procedures at high capacity airports, such as LAX, required lower altitudes than step down approaches. Not only does this negate the benefits of CDAs, but actually increases noise and pollution.