Departure noise limits Fixed noise

Departure noise limits
Fixed noise monitors at the airport located at approximately 6.5km from start-of-roll (SOR). There are 10 fixed monitors around Heathrow.
There are noise limits applied at these fixed noise monitors for departing aircraft. During the night quota period (2330-0600) departure noise limit is 87dBALmax. the remainder of the night period (2300-2330 and 0600-0700) noise limit is 89dBALmax. There is also a daytime noise limit of 94dBALmax.
The location and distance of the fixed noise monitors were decided in the early 1990’s after consultation. Relating the noise limits to a reference distance 6.5 km from start-of-roll encourages aircraft operators to gain height as quickly as possible and then reduce engine power and noise at the earliest opportunity. There is also a requirement for departing aircraft to attain at least a 1000 feet altitude when passing the fixed noise monitors. We fine airlines. whose aircraft breach the noise limits.