Explanation for the various Approach types in the Airbus A320 family.
There are two approach techniques for a standard ILS Approach.
1. Decelerated Approach
2. Early Stabilzed Approach
The Decelerated Approach is most commonly used since it uses a configuration that allows the aircraft to descend on the Glidepath at minimum power and yet is able to maintain addequate airspeed i.e. not accelerating). The goal is to reach the Glideslope at the Final Approach Altitude at Flaps 1 and S-Speed. When in NAV mode with managed speed, the approach phase will activate automatically when the deceleration pseudo-waypoint (D) is overflown.
Once the approach phase is active and in managed speed mode, the commanded speed will be Vapp. However, the FMGS will maintain Green Dot speed until Flaps 1 is selected. With Flaps 1 selected, the aircraft will slow down to S-Speed and maintain it automatically.
The Glidesplope is intercepted preferably in Flaps 1 at S-Speed and flown in this configuration until about 2500 ft AGL. There Flaps 2 is selected and the deceleration towards F-Speed begins. However, there might be circumstances (Steep Glideslope, Tailwind) where Flaps 2 is selected at Glideslope interception in order to keep the aircraft from accelerating towards VFE (max. flaps/slats extended Speed).
The important limit that you have to respect is at 1000 ft above threshold elevation. At this point the aircraft needs to be "stable", meaning it must be at final configuration (Gear and Flaps), at adequate airspeed (max. Vapp + 10 kts) and on Path (GS and LOC). Should this not be the case a Go-Around has to be flown unless you are in VMC (Visual Conditions). In this case the limit for some airlines is 500 ft above Threshold.
Early Stabilized Approach
The Early Stabilized Approach refers to a technique where the aircraft reaches the Final Descent Point in the landing configuration and at Vapp. In order to get an adequate deceleration pseudo waypoint, the pilot must enter the Vapp speed as a speed constraint at the Final Descent Point.
The reason to use the Early Stabilzed Approach technique is for example when flying a Non-Precision Approach where you want to avoid large configuration changes during the final descent, destabilizing the descent profile. Another reason could be a very low Final Approach Altitude. There are approaches where the Final Approach Altitude is only.
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