From 2014 :
"8 On Arrivals Noise Controls the paper set out ERCD’s details of the monitoring exercise on behalf of the ANMAC Technical Working Group on ground-based visual observations of approaches to Heathrow Airport.
The aim of the study was to compile statistics on the distance to landing for ’wheels down’ with wheels down being used as a proxy for an aircraft not being in an LP/LD configuration.
The incidence of LP/LD at Heathrow was approximately 90% of aircraft at 8 nautical miles from threshold.
For the sample of flights analysed, the average measured noise benefit resulting from the use of LP/LD was approximately 3dB at 7.5 nautical miles from threshold.
Around 55 flights (10% of the total) had their landing gear down prior to reaching 8 nautical miles from threshold. The results from the exercise would help in updating the Arrivals Code of Practice.
9 The following points came up in discussion:
• It would be good to know the factors that lead to the early deployment of landing gear. A workshop would be useful and it was noted that a NATS trial/workshop at Edinburgh airport with the airlines on CDA has led to a big improvement.
• It was considered that short spacing between aircraft and the tight speed controls at Heathrow may be a factor.
• Heathrow would consider the issue with the operators.
• A similar monitoring exercise study was planned for Gatwick in the coming months.
• The exercise indicated that a noise monitor at the London Wetland centre could be useful."
The Wetlands noise monitor is now in place. I think some video work on pics of planes to try to use automatic image recognition for gear deployment has been done.