Description
From 1962 until 1993, operations at Heathrow were subject to a simple limit on the number of aircraft movements that were allowed to take place during the night period.
In 1993 a new Quota Count system was introduced based on aircraft noise certification data. Each aircraft type is classified and awarded a quota count (QC) value depending on the amount of noise it generated under controlled certification conditions. The quieter the aircraft the smaller the QC value. Aircraft are classified separately for landing and take-off. Take-off quota count values are based on the average of the certificated flyover and sideline noise levels at maximum take-off weight, with 1.75 EPNdB added for Chapter 2 aircraft. Landing quota count values are based on the certificated approach noise level at maximum landing weight minus 9.0 EPNdB.
Aircraft were originally divided into six QC bands from 0.5 to 16, but following a review by the Department for Transport a seventh category - Quota Count 0.25 - was added in March 2007.
| Noise Classification | Quota Count |
|---|---|
| Below 84 EPNdB | Exempt |
| 84 - 86.9 EPNdB | 0.25 |
| 87 - 89.9 EPNdB | 0.5 |
| 90 - 92.9 EPNdB | 1 |
| 93 - 95.9 EPNdB | 2 |
| 96 - 98.9 EPNdB | 4 |
| 99 - 101.9 EPNdB | 8 |
| Greater than 101.9 EPNdB | 16 |
The quota count doubles with each increase of 3 dB which corresponds to an approximate doubling of noise power. However, due to the logarithmic nature of human aural perception, this 3 dB change is perceived as only a small change in the noise level.
Airports operating the system have a fixed quota for each of the summer and winter seasons. As each night-time aircraft movement takes place, an amount of this quota is used depending on the classification of the aircraft. For example, the Boeing 747-400 is classed as QC/2 on landing and QC/4 on takeoff, while the much larger Airbus A380 is rated QC/0.5 on landing and QC/2 on takeoff. The quieter A380 aircraft therefore use up an airport's noise quota approximately 42% of the rate of the 747, thus providing airlines with an incentive to operate quieter types of aircraft.
Read more about this topic: Quota Count System
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