Damla Benli

                          Noise measurement points

An aeroplane, when tested in accordance with the flight test procedures of 2.6, shall not exceed the noise levels specified in 2.4 at the following points:

a) Lateral Noise Measurement Point: The point on a line parallel to and 650 m from the runway centre line, or extended runway centre line, where the noise level is a maximum during take-off;

b) Flyover Noise Measurement Point: The point on the extended centre line of the runway and at a distance of 6.5 km from the start of roll; and

c) Approach Noise Measurement Point: The point on the ground, on the extended centre line of the runway, 120 m (394 ft) vertically below the 3° descent path originating from a point 300 m beyond the threshold. On level ground this corresponds to a position  2000 m from the threshold.

            NOISE MEASUREMENT PROCEDURES

The applicant should submit to the certificating authority for their review and approval technical procedures for the measurement of aircraft noise certification levels. The technical procedures described in the following sections of this chapter should be considered as generally appropriate for all aircraft types. For procedures specific to Appendices 2, 4 and 6 see respectively Chapters 4, 5 and

         

    Test site selection

For aeroplanes, when the flight path intercept equivalent test procedure is used, and for helicopters, it may not be necessary for the test site to be located at an airport. Details of the proposed noise certification test-site locations should be submitted to the certificating authority for review and approval. Some test-site criteria that could support selection of a non-airport test site include level terrain, reduced air traffic, reduced ambient noise, improved weather conditions (temperature, humidity and wind), improved microphone placement, availability of field surveys, improved locations for aircraft position monitoring and improved pilot sight and handling.

*Terrain:

Uneven terrain having features such as mounds or furrows can result in reflections that could influence the measured sound levels. Vegetation can reduce the amount of sound that is reflected from the ground surface. In most cases this effect results in a reduced sound level, but under some circumstances the level may be higher. Testing over a smooth hard surface, such as a paved area, will generally result in a higher sound level.

*Grass:

For noise measurement points under the flight path 7.5 m (25 ft) radius circles of mowed grass (not exceeding 8 cm (3 in) height) are acceptable. For noise measurement points located to the side of the flight path, the grass may be mowed in a semicircle of 7.5 m (25 ft) radius facing the line of flight.

*Snow:

Snow in the area surrounding the noise measurement points may provide excessive absorption of aircraft sound reflected from the ground. Noise measurement points have been approved when snow within a 15 m (50 ft) radius of the noise measurement points has been removed. However, snow should not be piled at the borders facing the line of flight.

*Ploughed fields:

Earthen or sandy surfaces within a 7.5 m (25 ft) radius of the noise measurement points shall be reasonably tamped down. Ploughed furrows, silt or soft, powdered surfaces are unacceptable.

*Obstructions:

Obstructions in the vicinity of the noise measurement points such as buildings, walls, trees, vehicles and test personnel, if close enough, may be unacceptable because of reflections that influence measured noise levels. There should be no obstructions that significantly influence the sound field from the aircraft within a conical space above a point on the ground vertically below the microphone at each noise measurement point. The cone is defined by an axis normal to the ground and by a half angle of 80º (75º for light propeller-driven aeroplanes) from the axis as illustrated in Figure 3-1.

*Anomalous meteorological conditions:

Certain geographical areas are more susceptible to anomalous meteorological conditions than others (i.e. large variations, or inversions, of temperature or humidity, excessive turbulence or thermally induced vertical winds). The applicant may conduct certification testing only as approved by the certificating authority.

Maximum noise levels

The maximum noise levels of those aeroplanes covered, when determined in accordance with the noise evaluation method of Appendix 1, shall not exceed the following:

a) at lateral and approach noise measurement points: 108 EPNdB for aeroplanes with maximum certificated take-off mass of 272 000 kg or over, decreasing linearly with the logarithm of the mass at the rate of 2 EPNdB per halving of the mass down to 102 EPNdB at 34 000 kg, after which the limit remains constant;

b) at flyover noise measurement point: 108 EPNdB for aeroplanes with maximum certificated take-off mass of 272 000 kg or over, decreasing linearly with the logarithm of the mass at the rate of 5 EPNdB per halving of the mass down to 93 EPNdB at 34 000 kg, after which the limit remains constant.

The maximum noise levels of those aeroplanes covered, when determined in accordance with the noise evaluation method of Appendix 1, shall not exceed the following:

*At lateral noise measurement point

106 EPNdB for aeroplanes with maximum certificated take-off mass of 400 000 kg or over, decreasing linearly with the logarithm of the mass down to 97 EPNdB at 35 000 kg, after which the limit remains constant.

*At flyover noise measurement point

a) Aeroplanes with two engines or less:

104 EPNdB for aeroplanes with maximum certificated take-off mass of 325 000 kg or over, decreasing linearly with

the logarithm of the mass at the rate of 4 EPNdB per halving of mass down to 93 EPNdB, after which the limit remains

constant.

b) Aeroplanes with three engines:

As a) but with 107 EPNdB for aeroplanes with maximum certificated take-off mass of 325 000 kg or over as defined b), whichever is the lower.

 c) Aeroplanes with four engines or more:

As a) but with 108 EPNdB for aeroplanes with maximum certificated take-off mass of 325 000 kg or over or as defined by b), whichever is the lower.

*At approach noise measurement point

108 EPNdB for aeroplanes with maximum certificated take-off mass of 280 000 kg or over, decreasing linearly with the logarithm of the mass down to 101 EPNdB at 35 000 kg, after which the limit remains constant.

      

   EQUATIONS FOR THE CALCULATION OF NOISE LEVELS AS A FUNCTION OF TAKE-OFF MASS

Trade-offs

    If the maximum noise levels are exceeded at one or two measurement points:

a) the sum of excesses shall not be greater than 4 EPNdB, except that in respect of four-engined aeroplanes powered by engines with a bypass ratio of 2 or more and for which the application for a certificate of airworthiness for the prototype was accepted, or another equivalent prescribed procedure was carried out by the certificating authority, before 1 December 1969, the sum of any excesses shall not be greater than 5 EPNdB;

b) any excess at any single point shall not be greater than 3 EPNdB; and

c) any excesses shall be offset by corresponding reductions at the other point or points.

Test procedures

Take-off test procedure

Average take-off thrust2 shall be used from the start of take-off to the point at which a height of at least 210 m (690 ft) above the runway is reached, and the thrust thereafter shall not be reduced below that thrust which will maintain a climb gradient of at least 4 per cent.

A speed of at least V2 + 19 km/h (V2 + 10 kt) shall be attained as soon as practicable after lift-off and be maintained throughout the take-off noise certification test.

A constant take-off configuration selected by the applicant shall be maintained throughout the take-off noise certification demonstration test except that the landing gear may be retracted.

Approach test procedure

The aeroplane shall be stabilized and following a 3° ± 0.5° glide path.

The approach shall be made at a stabilized airspeed of not less than 1.3 VS + 19 km/h (1.3 VS + 10 kt) with thrust stabilized during approach and over the measuring point and continued to a normal touchdown.

The configuration of the aeroplane shall be with maximum allowable landing flap setting.