V1GO - All approaches into Heathrow Gatwick and Stansted are monitored for compliance with Continuous Descent Approach (CDA) procedures at all times.
CDAs are seen by the government as a key factor in noise reduction in the vicinity of the three London airports.
For monitoring purposes, a descent is deemed to have been continuous provided that no segment of level flight longer than 2.5 nm occurs below 6000ft QNH.
Level flight is interpreted as any segment of flight having a height change of not more than 50ft over a track distance of 2nm or more as recorded in the airport Noise and Track-Keeping system.
Due to constraints of the tracking system and differences in elevation of the airports, CDA achievment is monitored from a height of 5500ft aal.
It is recognised that CDAs to runway 05 at Stansted are not possible at the moment due to airspace constraints and to a lesser extent there are restrictions at Gatwick.
Hope this helps.
