 Planning guidance on aircraft noise advises that " in some circumstances the public perceive general aircraft noise levels as more disturbing than similar levels around major airports . " This is a result of the tonal characteristics of light aircraft engines and the activities they are engaged in , including : repetitive circuit flying at low @-@ altitude near an aerodrome , during which aircraft are audible for long periods ; slow climbing aircraft engaged in parachute drop or glider <unk> activities concentrated around the drop zone or aerodrome , also audible for long periods ; erratic and repetitive engine noise from aircraft engaged in aerobatics ; and piston @-@ engines on full power in areas of low background noise , leading to the perception that such noise is more <unk> . In an attempt to alleviate these problems , the majority of aerodromes implement noise abatement procedures designed to route aircraft away from noise sensitive areas , and more than 50 are required by the government to provide <unk> facilities in which local concerns can be raised with aerodrome operators . 
