Appendix 3.1              Review of Noise Criteria for Helicopter Noise





This technical note aims at investigating the appropriate helicopter noise metric other than Lmax to be adopted for evening time criteria for helicopter noise assessment.  This exercise covers a critical review of helicopter noise criteria adopted in Hong Kong and overseas countries, and international standards.  Based on the results of the review, the recommended noise metric/metrics assessment criteria for evening period (1900 – 2300 hours) would be adopted in the helicopter noise assessment of the Environmental Impact Assessment (EIA) Study for Expansion of Heliport Facilities at Macau Ferry Terminal.  


The study was conducted with the following objectives:

(1)        To review the existing Hong Kong helicopter noise criteria;

(2)        To review the helicopter noise criteria in overseas countries.;


To identify the appropriate noise metric/metrics other than Lmax with reference to the review findings on overseas criteria and past research studies.


review of existing criteria in hong kong


In Hong Kong, helicopter noise criteria are a guideline as stipulated in the Hong Kong Planning Standard and Guideline until the establishment of Environmental Impact Assessment Ordinance (EIAO).  As a Designated Project under the EIAO, the helicopter noise levels are under the control of the statutory requirements.  The history of helicopter noise criteria in Hong Kong is de scribed as following paragraphs.


Hong Kong Planning Standard and Guidelines


In June 1989, the Government published a major policy document, the White Paper on 'Pollution in Hong Kong'.  The White Paper placed considerable emphasis on environmental planning, stating that "serious environmental pollution in Hong Kong is an unfortunate by-product of economic success and population growth.  One of the Government's major priorities is to halt the decline in environmental conditions and to do more to improve our environment".


The Hong Kong Planning Standards and Guidelines (HKPSG) was established in 1991 and Chapter 9 provides guidance for including environmental considerations in the planning of both public and private developments.  It applies both to the planning of permanent or temporary uses which will have potential to cause significant changes to the environment or which are sensitive to environmental impacts.  The standards and criteria included in the HKPSG will need to be applied with a degree of flexibility and not in isolation.  But any departure from them should not be accepted without full consideration of all the implications and the long-term adverse effects on living conditions in Hong Kong.


As stated in Section 4.2.3 of the HKPSG, night-time operations of helicopters will generally be more intrusive than daytime operations.  For application in Hong Kong, the helicopter noise is presented in terms of Lmax dB(A) during daytime period (07:00 – 19:00) and the noise criteria for residential development and commercial developments are as follows:





Residential Development             Lmax 85 dB(A)

OfficeEducational Institution                                        Lmax 90 dB(A)


Note: The standard applies to the external façade at operable windows for ventilation of habitable rooms.


Advice from EPD should be sought if it is anticipated that helicopters will be operated:

(a)                 in a tranquil environment; or

(b)                 during late-evening and night-time.



Environmental Impact Assessment Ordinance (EIAO)


In 1998, Environmental Protection Department (EPD) established the EIAO against pollution in the planning stage of new development projects and proposed residential developments with a projected population greater than 200,000 to undertake an environmental impact assessment during planning stage.  This statutory provision includes the issue of helicopter noise.  In the EIA stage, compliance of helicopter noise standards (Lmax) under the HKPSG at all residential and office facades is required when the proposed project is a designated project under the EIAO.  However, this noise criterion is applied for daytime period (07:00-19:00) only.


review of existing criteria in OVERSEAS COUNTRIES


In considering appropriate evening time criteria for helicopter noise to be adopted in this EIA Study, review on existing helicopter noise criteria of overseas countries was carried out, as a guide to the noise levels considered appropriate in sensitive areas.   In this section, the noise criteria & noise metric of different countries and international standards for helicopter noise impact is discussed in the following paragraphs. 


Federal Aviation Administration – FAA


The FAA Advisory Circular Number 150-5020-1, entitled “Noise Assessment Guidelines for New Helicopters recommends the use of a cumulative noise measure, the 24-hour equivalent sound level (Leq(24)), so that the relative contributions of the heliport and other sound sources within the community may be compared.  The Leq(24) is similar to the Ldh used in assessing the impacts.  The helicopter Leq(24) values are obtained by logarithmically adding the single-event Sound Exposure Level (SEL) values over a 24-hour period but without any weighting factors for time periods.


The FAA recommends exterior noise criteria for individual heliports based on the types of surrounding land uses.  The following table shows the recommended noise levels.









Normally Compatible Community Sound Levels

Type of Area

Lt 24













Source: FAA Advisory Circular Number 150-5020-2, 1983


The maximum recommended cumulative sound level (Leq(24)) from the operations of helicopters at any new site should not exceed the ambient noise already present in the community at the site of the proposed heliport.


Ontario, Canada


There are no specified helicopter noise criteria but it can make reference to the aircraft criteria.  The Ministry of the Environment assesses the impact of aircraft noise on planned noise sensitive land uses and the suitability of development. The noise impact assessment is based on the NEF/NEP contours, approved by Transport Canada.


The NEF rating is based on the Effective Perceived Noise Level (EPNL) which is given by the Perceived Noise Level (PNL), adjusted for the duration of fly-over and the presence of discrete tones. The PNL is the maximum perceived noise level calculated from the third octave band noise levels. The NEF value is then calculated from the EPNL for each fly-over, the number of fly-overs and adjustments for day-time and night-time operations. The NEP is similar to the NEF with the exception that the NEP uses a longer time frame. Neither NEF nor NEP can be measured directly and can only be calculated from measured quantities.


The aircraft noise criterion in terms of an NEF/NEP value in any outdoor area, including the outdoor living area is shown in following table. The criterion applies to the entire 24-hour period. The distance separation from the airport and, consequently, the location of the noise sensitive land use with respect to the NEF/NEP contours, is the only measure that controls the outdoor noise impact.


Time Period


24 hours





No standard for helicopter noise but can make reference to the aircraft noise criteria.  In accordance with the provisions of Article 16 of the Basic Environment Law (Law No. 91 of 1993), the environmental conditions relating to aircraft noise standards are notified as follows.

The standards for regulating the environmental conditions of aircraft noise (hereinafter referred to as "environmental quality standards") are established as follows according to Article 9 of the Basic Law for Environmental Pollution Control and the target dates thereof. The maintenance of the standards is desirable to preserve the living environment and to contribute to protecting people's health.


The values of the environmental quality standards are established for each category of area shown in following table.  Prefectural governors shall designate the category of area.



Category of area

Standard value (in WECPNL)


70 or less


75 or less

Note: Area category I refer to areas used exclusively for residential purpose and Area category II refers to other areas where the normal living conditions shall be preserved.


The values of the environmental quality standards above are measured and evaluated by the following method.

(1) Peak levels of aircraft noise, which is higher than background noise level by 10 dB or more, and the number of such aircraft, shall be recorded in dB (A) for, in principle, for seven consecutive days.

(2) Measurements shall be carried out outdoors and at points selected as representing the points of aircraft noise in the area concerned.

(3) The timing of measurements shall be chosen as representing the duration of aircraft noise at the point of measurements, taking into consideration the flight conditions and meteorological conditions including wind directions.

(4) The aircraft noise shall be evaluated as follows. The WECPNL values for each day will be calculated from peak levels of aircraft noise and numbers recorded under subparagraph (1) using the following equation. The energy mean of daily WECPNL values is used to calculate the noise level in question.





10 log10N





Note: dB(A) stands for the energy mean of all peak levels of any one day, and N stands for a value calculated by the following equation: N = N2 + 3N3 + 10(N1 + N4), where N1 is the number of aircraft between 0:00 a.m. and 7:00 a.m., N2 the number between 7:00 a.m. and 7:00 p.m., N3 the number between 7:00 p.m. and 10:00 p.m., and N4 the number between 10:00 p.m. and 12:00 p.m.


(5) Anyone of the following instruments can be used for measurement: the sound level meter provided for in Japan Industrial Standards C-1502, precision sound level meter under International Electric Standards Conference Pub/179, or any other equivalent instrument. In these cases, A-weighted calibration and slow dynamic response shall be used.


The environmental quality standards shall not be applied to areas around airports where there are 10 or less daily landings and take-offs and to those around airports in remote islands. 

United States of America


There are no specified noise criteria for helicopter noise. The helicopter noise impact will be evaluated in assessing based on the same standards as for aircraft noise.


Anabeim, California


According to Anabeim General Plan/Zoning Code, the maximum recommended cumulative sound level Leq(24) from the operations of helicopters at any new site should not exceed the ambient noise already present in the community at the site of the proposed heliport.   


The exterior noise criteria for individual heliports based on the types of surrounding land uses.  The following table shows the recommended noise levels.



Normally Compatible Community Sound Levels

Type of Area

Lt 24















San Francisco

The noise impacts of helicopter operations were based on the cumulative noise exposure of multiple operations over daily periods.  The noise method that was utilized was Day-Night Average Sound Level (DNL), Ldn.  This noise metric was based on social survey research that was conducted over the years to quantify people’s reaction to noise exposure levels in the community.  It divides 24 hours into two time periods: day (0700 – 2200) and night (2200 – 0700).  For events that occur during the night time hours, a night penalty of 10dB is added to take into account the greater sensitivity of people to sounds that occur during these time periods.


The DNL noise results range from 65 dB DNL to 68 dB DNL by measuring noise levels for the background ambient around San Francisco general hospital.


Boston / Washington

An annual average of DNLs is used by the Federal Aviation Administration to describe airport noise exposure.  Areas with noise impacts less than 65dB DNL are considered “compatible” with residential use; areas at or above 65dB DNL are designated “incompatible” with residential use.


For night time noise, between the hours of 22000 – 0700, an additional 10 decibels is added to compensate for sleep interference and other disruptions caused by night time noise.


New York State, Department of Environment of Environmental Conservation – New York

For noise assessment, equivalent sound level (Leq) correlates well and can be combined with other types of noise analyses such as Composite Noise Rating, Community Noise Equivalent Level and day-night noise levels characterized by Ldn where an Leq(24) is measured and 10dB(A) is added to all noise levels measured between 2200 – 0700.  These different types of noise analyses basically combine noise measurements into measures of cumulative noise exposure and may weight noise occurring at different times by adding decibels to the actual decibel level.


California - FAA

In California, noise levels are described using the Community Noise Equivalent Level (CNEL) metric.  The terminology is the same as the DNL except that it includes a 4.77 dB penalty for each aircraft event that occurs between 1900 – 2200, and a 10 dB penalty for each aircraft event that occurs between 2200 – 0700.




In year 1978, The Federal Government via the FAA established a noise threshold which it thought residents should be expected to tolerate, the threshold level was set at 65 DNL.  It was agreed that if the DNL exceeded 65 dB, the airport operator or local government could implement mitigation procedures such as buying out residents living within the 65 DNL contour, or sound proof the owner’s home.  The Environmental Protection Agency (EPA) argued that for people’s health and peace of mind, the threshold should be set lower, 55 DNL.  However, the aircraft technology at that time could not achieve better performance that 65 DNL, and the Government knew that it they used a lower threshold

, it would have to spend hundreds of billions of dollars to solve the noise problem at the receivers.  After that, the American National Standards Institute (ANSI) codified the threshold levels for human activities, the standard specified that threshold above 65 DNL is incompatible with residential living.


United Kingdom


There is no restriction for helicopter noise but a control plan including noise criteria would be established for individual project.  Followings are some examples of the project relating to the helicopter. 


Noise Insulation Grant Scheme (NIGS)


Night time criteria, which offers to provide noise insulation grants to homes near located military airfields which are exposed to significant night time flying (2300 – 0700) and which are subject to recurring maximum sound levels (defined as greater than 20 movements) of 82dB(A) or greater.


Night time rotary wing criteria, which offers to provide noise insulation grants to homes located near military airfields which are exposed to significant night time flying (2300 – 0700) and which are subject to this nightly average sound level.


Spelthorne Borough Local Plan


Recommended Noise Exposure Categories for New Dwellings Near Existing Noise Sources under this project is as follows:


Noise Levels Corresponding to the Noise Exposure Categories for New Dwellings LAeq, T dB


Noise Exposure Category

Noise Source





Air Traffic

0700–2300 hrs

2300–0700 hrs





57 – 66

48 – 57


66 – 72

57 – 66




Key to Noise Categories (NEC)

A          Noise need not be considered as a determining factor in granting planning permission, although the noise level at the high end of the category should not be regarded as a desirable level

B          Noise should be taken into account when determining planning applications and, where appropriate, conditions imposed to ensure an adequate level of protection against noise.

C          Planning permission should not normally be granted.  Where it is considered that permission should be given, for example because there are no alternative quieter sites available, conditions should be imposed to ensure a commensurate level of protection against noise.

D          Planning permission should normally be refused.


New Zealand


New Plymouth District Plan 


A set of helicopter noise standard is proposed for the helicopters operating from helicopter landing areas under this project.  The maximum noise levels, measured at any point within the boundary of any receiving site within the residential environmental area or measured at the notional boundary within the rural environment area should not be higher than Ldn 50 dB(A) when day-night average sound level over any period of 5 consecutive days or maximum noise levels and its Lmax should not be higher 70 dB(A) on any day between 10 pm to 7 am the following day.