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Noise from
Arriving Aircraft
An Industry
Code of Practice
2nd Edition – November 2006

Executive Summary
This voluntary Code of Practice has been compiled by a group
representing airlines, air traffic control, airports, the Civil Aviation
Authority (CAA) and the Department for Transport (DfT). It is
primarily concerned with Heathrow, Gatwick and Stansted airports,
although much of the content is equally applicable to other airports
in the UK and worldwide. Recent successes are noted and
practical steps are set out along with longer-term advice
concerning measures to reduce noise from arriving aircraft. 
The key factor identified is the noise benefit that can be obtained
from greater achievement of continuous descent approaches
(CDAs as defined in this document).
Introduction
1.  During the period 1994-99 Government considered the
feasibility of setting noise limits for arriving aircraft through the
then Department for Transport, Local Government and the
Regions’ (now DfT) Aircraft Noise Monitoring Advisory
Committee (ANMAC). This was considered in some depth,
including the formation of a technical working group whose
work was published in the report ‘Noise from Arriving Aircraft:
Final Report of the ANMAC Technical Working Group’ in
December 1999. This considered all aspects of variability of
noise from arriving aircraft in great detail. The study
summarised the causes of variability of noise heard under the
path of arriving aircraft – illustrated in Fig 1.
1

Noise from Arriving Aircraft – An Industry Code of Practice
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2

2.  In the light of the ANMAC findings, the then Aviation Minister
decided against imposing operational noise limits for arriving
aircraft. On 10 February 2000 he announced that a Code of
Practice should be established to address this issue.
Representatives of the DTLR, NATS, BAA, British Airways,
Airtours (now operating as My Travel) and CAA/ERCD compiled
the original version of the Code which was published in
February 2002.
3.  A review of the Code was undertaken by a similar group (now
including EasyJet and Virgin Atlantic Airways) in 2003/4. The
detailed results of the review were presented to ANMAC.
The review, this document and a condensed version of this
document can be found on-line at www.dft.gov.uk/aviation
4.  Notwithstanding the success of the Code to date the review
group also agreed a number of recommendations which are
outlined throughout this document. Ten key factors that could
lead to further improvements are summarised at the end of
this document. 
Scope
5.  Using the experience and knowledge of all participants, this
2nd edition of the Code of Practice has been produced to
identify steps which could reduce the noise generated by
arriving aircraft. As a result the Code is a technical document
which is primarily written for pilots and air traffic controllers, but
it also includes advice to relevant parties such as airports and
the regulators.
6.  This work has concentrated on Heathrow, Gatwick and Stansted
although it is recognised that much of the Code is potentially
relevant to other airports internationally. It should be noted
that CDA arrival procedures are not possible under normal
operations for approaches to runway 05 at Stansted due to
3

Noise from Arriving Aircraft – An Industry Code of Practice
airspace constraints (although such approaches at night are
monitored for CDA achievement). To a lesser extent there are
also restrictions on the application of CDA due to airspace
constraints at Gatwick. Any change to the airspace around
Stansted would seek where possible to facilitate CDAs to
runway 05.
7.  Nothing in this Code shall take precedence over the
requirement for safe operation and control of aircraft at all
times. For the avoidance of doubt, all recommendations are
to be read as being “subject to the requirements of safety”.

Background
8.  Approach noise is a specific measurement in the International
Civil Aviation Organization (ICAO) noise certification process
whereby aircraft types are assessed and certificated. For fixed
wing aircraft the approach noise certification measurement
point is very close in to the airport (2 km from threshold), where
configuration and flight conditions are very tightly defined. The
ANMAC Technical Working Group report showed that further
away from the airport there is significant variability in arrivals
noise levels for a given aircraft type. The study identified the
many factors which caused this variability, and determined what
measures could best mitigate the higher noise levels for aircraft
type (i.e. those at the upper end of the range of variability). It was
recognised however that the safety requirements of the industry,
especially ATC procedures and operations in poor weather,
place constraints on which factors can be modified to reduce
noise. Within these constraints, this Code identifies measures
that can deliver reductions in arrivals noise.
9.
The report highlighted CDA, in descent from 6000ft to
establishment on the final approach glideslope, as the leading
technique for reducing arrivals noise (this is illustrated at Fig 2).
4

This Code of Practice therefore strongly emphasises measures
intended to improve achievement of CDA.
Figure 2: Benefits of approach noise mitigation
procedures

6
B747-400
CDA: benefit of true CDA
5
approach relative to 5nm level
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10. It is important to note that, for modern jet aircraft (high by-pass
ratio turbofans), the benefits of increased altitude typically
outweigh those gained from a low power/low drag technique
(see paragraph 16) prior to joining final approach, where there
is to some extent a choice or trade-off between the two.
Controllers and pilots should therefore seek to facilitate/achieve
CDA wherever possible. In general a level segment of a given
length will result in less noise at ground level the higher it is
flown. For example a level segment at say 2500ft is likely to
result in a noise level of the order of 8dB greater than if it were
flown at 5,000ft. It is acknowledged that controllers and pilots
are not typically confronted by a simple choice of this sort for
individual flights, but it is important that the broad principle
should be widely understood and applied wherever possible.
This is further illustrated in Fig 3.
5

Noise from Arriving Aircraft – An Industry Code of Practice
Figure 3: Disbenefit of level intercepts relative to 
‘pure’ CDA approach

6
B747-400: 5nm of level flight
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11. In addition to the noise benefit, the use of CDA techniques also
reduces fuel burn and hence emissions thereby producing both
an overall environmental benefit plus cost savings to airline
operators.
12. ICAO Circular 303 notes that: ‘Descent profile optimization and
the use of continuous descent approaches can offer significant
potential fuel-saving benefits’, and that ‘reductions of between
200 kg and 400 kg per flight, depending on aircraft size, are
possible.’
Definition of CDA
13. In the first edition of the code it was strongly recommended
that detailed CDA requirements be published in the UK AIP.
This has been achieved, a definition of CDA is published in the
UK Aeronautical Information Package (AIP) at GEN 1.7 Table
1.7.2 ‘UK Definitions for Terms Used by ICAO’.
6

What is a CDA? 
A noise abatement technique for arriving aircraft in which the
pilot, when given descent clearance below Transition Altitude
by ATC, will descend at the rate best suited to the
achievement of continuous descent, whilst meeting the ATC
speed control requirements, the objective being to join the
glide-path at the appropriate height for the distance without
recourse to level flight.

Specific conditions for Heathrow, Gatwick and Stansted are
detailed in paragraph 15.
14. The use of CDA and LP/LD approach techniques, subject to
compliance with ATC requirements, is outlined at UK AIP ENR
1.1.3 paragraph 2.3.1.
15. The theoretical “ideal” CDA profile for Heathrow, Gatwick and
Stansted is a descent at 3° from 6000ft, as illustrated in 
Fig 4. A number of factors need to be taken into account in
defining CDA:
• ICAO Doc 8168 PANS-OPS Vol II Pt III, paragraph 5.6
requires that, on the intermediate approach segment, “…a
horizontal segment with a minimum length of 2.8km (1.5nm)
should be provided prior to the final approach for Category
C and Category D aircraft …”;
• the standard ICAO safety requirement of intercepting the
final approach glideslope from below;
• at a given altitude, a level segment used to decelerate an
aircraft, at or near thrust-idle, will tend to generate less
noise than an extended level segment at or near a constant
airspeed;
7

Noise from Arriving Aircraft – An Industry Code of Practice
• the monitoring capabilities of the Noise and Track (NTK)
system in use at Heathrow, Gatwick and Stansted, including
altimeter and radar tolerances, software interpolation, etc;
• the distance required by modern jet transport aircraft to
decelerate in level flight; this is reflected in the choice of
2.5nm for the maximum level segment length at the three
airports;
• CDA should start from as high a level as possible given the
constraints of the airspace. In the London TMA it is
recognised that the highest practicable level a CDA can
commence for Heathrow, Gatwick and Stansted is 6000ft.
8

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9

Noise from Arriving Aircraft – An Industry Code of Practice
For practical purposes a working definition of CDA as
defined in AIP for Heathrow, Gatwick and Stansted is as
follows: an arrival is classified as a CDA if it contains, below
an altitude of 6000ft:

– no level flight; or
– one phase of level flight not longer than 2.5nm 
For monitoring purposes, due to the constraints of the NTK
system and the different elevations of airports, CDA
achievement is monitored below a height of 5,500ft above
aerodrome level (aal) at Heathrow, Gatwick and Stansted
airports.

‘Level flight’ is interpreted as any segment of flight having a
height change of not more than 50ft over a track distance of
2nm or more, as recorded in the airport NTK system.

Definition of Low Power/Low Drag (LP/LD)
16. A definition of Low Power/Low Drag is published in the UK
Aeronautical Information Package (AIP) at GEN 1.7 Table 1.7.2
‘UK Definitions for Terms Used by ICAO’.
What Is Low Power/Low Drag?
“A noise abatement technique for arriving aircraft in which
the pilot delays the extension of wing flaps and undercarriage
until the final stages of the approach, subject to compliance
with ATC speed control requirements and the safe operation
of the aircraft.”

17. This broadly means the aircraft being in as ‘clean’ a
configuration as possible, for as long as possible. During the
intermediate approach, including the closing heading, and on
final approach, thrust reductions should be achieved where
10

possible by maintaining a ‘clean’ aircraft configuration and by
landing with reduced flap. In practice at Heathrow, Gatwick and
Stansted this is broadly interpreted to mean the minimum drag
configuration (flaps and undercarriage) consistent with ATC
speed controls. In turn ATC speed controls are specified to be
broadly compatible with LP/LD for most types of aircraft.
Operational Issues for Air Traffic Controllers
Continuous Descent Approach Procedure
18. From an Air Traffic Control perspective the aim of a CDA is to
provide pilots with the ATC assistance necessary for them to
achieve a continuous descent during intermediate and final
approach, at speeds which require minimum use of flaps etc.
This has significant benefits in terms of noise produced
beneath the approach area, and in reduction of fuel used.
19. CDA procedures requires ATC to apply specific or minimum
speeds to inbound aircraft and to pass adequate “range from
touchdown” information.
20. Except in exceptional circumstances, CDAs are to be employed
at all times for aircraft inbound to Heathrow, Gatwick and
Stansted. (Note: CDAs for runway 05 at Stansted are still not
routinely possible due to conflicting airspace considerations.)
21. During the night quota period (2330-0600) all inbounds to
Heathrow, Gatwick and Stansted, irrespective of weight or type
of approach, are to be given descent clearance from Minimum
Stack level at a distance from touchdown which ensures that
inbounds are no lower than 6000ft when 20 track miles from
touchdown.
11

Noise from Arriving Aircraft – An Industry Code of Practice
22. In accordance with existing procedures, aircraft are then to be
vectored onto a closing heading that will position the aircraft to
intercept the extended runway centreline no closer than 10nm
from touchdown. Descent clearance below 3000ft is not to be
given until the aircraft is 10nm from touchdown.
23. During daytime operations the minimum joining point and
height are less than the night time criteria. Although absolute
minima are defined in the UK AIP, controllers should endeavour
to keep arrivals as high as possible for as long as possible and
not join the final approach lower than necessary, for minimum
noise impact reasons.
24. Previously aircraft were given ATC clearance to intercept the
ILS in two steps. At times this led to level segments before the
second clearance was given. One of these steps has been
eliminated, reducing the incidence of a level segment as the
aircraft intercepts the ILS. 
ATC Phraseology
Phraseology now approved is: ‘(callsign) when established
on the localiser, descend on the ILS’
.

25. NATS currently operate a scheme at the London airports where
a small randomly selected sample of night-time arrivals tracks
are analysed with a view to improving the accuracy of the track
distance given and pilot compliance.
Speed Control
26. The speeds to be flown during the approach phase are to be
specified by the controller, and will depend on the traffic
situation at the time. Standard speeds are published in the UK
AIP and should be adhered to whenever possible.
12

27. If the traffic conditions permit, a pilot may be requested to
maintain a higher than normal speed, or be advised that there
is “no ATC speed restriction”. The terms “keep your speed up”
and “maintain your speed” should be avoided except when
necessary for ATC separation purposes. The use of such
instructions may put a pilot into such a position that they may
have difficulty in achieving a reasonable approach because of
height/speed/range problems.
28. The standard speeds to be employed are as follows:
• During intermediate approach, i.e. after leaving the holding
facility to base leg approximately 6 miles prior to ILS
intercept: 210kt. 
Note: Pilots of some modern jet aircraft may request the use
of their “minimum clean” speed during this phase of flight;
commonly 220/230kts. Where possible, and subject to
separation requirements, this should be approved.
• Thereafter, and until established on final approach, the
highest possible speed between 160-180kt as required to
ensure accuracy of spacing;
• Established on final approach, until 4nm DME: 160kt
29. Instructed speeds are not subject to tolerance, and pilots will
fly them as accurately as possible.
Ranges from Touchdown
30. To assist pilots in the management of their descent, ranges
from touchdown are to be passed as follows:
• When first issuing descent clearance from stack level (a best
estimate only is required at this stage)
13

Noise from Arriving Aircraft – An Industry Code of Practice
• As soon as possible after contact with final director
• At any time if a previous estimate has become invalid, e.g.
following a change in landing sequence, or if the controller
considers that a range check would assist a pilot with
descent management.
31. If the DME is unserviceable, radar ranges should be passed on
the intercept heading to the ILS (these ranges should be as
accurate as possible).
Operational Issues for Flight Crew
32. All aircrew are encouraged to use all available data to assist in
the achievement of CDA.
33. CDA guidance detailing flight path angle/vertical speed for
pilots should be available to the pilot on the flight deck to
enable the planning and execution of a CDA approach. This
could be either within the FMC system or as charts/printed
material. Charts are provided in Figures 5 and 6, and the
corresponding numerical information is given in Tables 1 and 2.
The CAA intends to disseminate these charts by publication
either in the UK AIP or through an Aeronautical Information
Circular (AIC). 
14

Figure 5 – Flight Path Angles for CDA
6.0
Assumptions
Start altitude:
8000ft
8000ft QNH
1. Calculation
5.5
assumes 20sec of
7000ft
7000ft QNH
level flight (at 210kt
5.0
6000ft QNH
zero wind) before
)
g

5000ft QNH
descent
e
commences.
(d 4.5
6000ft
4000ft QNH
le
2. Assumes ILS
g
n

glideslope is
4.0
t
intercepted at
n
5000ft
10nm.
e
3.5
s
3. Assumes zero
e
wind, sea level
3.0
d
airfield.
ire
4000ft
2.5
q
e
2.0
1.5
1.0
10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27 28 29 30
Distance to run to touchdown (nm)
Figure 6 – Vertical Speed for CDA
2500
Start altitude:
Assumptions:
8000ft
1. Calculation
8000ft QNH
assumes 20sec of
7000ft QNH
level flight (at 210kt
7000ft
)
zero wind) before
2000
6000ft QNH
m
descent commences.
6000ft
5000ft QNH
(fp
t

2. Assumes 210kt
n
4000ft QNH
initially, 190kt on
e
c

base leg (max 6nm),
1500
and 170kt for last
e
D

2nm before joining
5000ft
f
ILS glideslope at
o
10nm.
te
a

3. Assumes zero
1000
wind, sea level
d
4000ft
airfield.
ire
u
q
e
R

500
0
10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27 28 29 30
Distance to run to touchdown (nm)
15

Noise from Arriving Aircraft – An Industry Code of Practice
30
2.2
1.7
1.3
-
-
30
850
650
500
300
150
.
29
2.3
1.8
1.3
-
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fpm
29
900
700
500
350
150
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28
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750
550
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1000
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14
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escent(fpm
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istance
istance
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16

34. A minimum rate of descent of 500 fpm is applicable for ATC
purposes for aircraft above the Transition Altitude following
STARs (this is a unique UK requirement). Although this
requirement does not continue into the approach phase of
flight, some pilots have in the past continued to descend at a
higher rate than necessary. To avoid confusion the UK AIP now
clarifies that the 500 fpm minimum ROD requirement does not
apply below Transition Altitude.
35. Depending on aircraft type and operators’ standard operating
procedures, it is recommended that descent should be
controlled by VNAV or Flight Path Angle (or Vertical Speed)
rather than FLCH or Open Descent.
36. Aircraft separation is achieved by vertical separation and
accurate vectoring supported by the use of accurate speed
control. It is important that ATC heading and speed instructions
are accurately and promptly adhered to. Descent using Vertical
Speed control may require the use of speedbrake or thrust to
maintain the correct speed.
37. Commensurate with safety and establishing a stabilised
approach, crews are encouraged to use the minimum flap
setting required for the requested ATC speed restriction and to
avoid the early lowering of the undercarriage. 
38. Research shows that noise is kept to a minimum by operating
the aircraft on a CDA and in as clean a configuration for as
long as possible. 
39. PANS-OPS (Vol 1 Pt V, 3.2.1) provides that “in noise abatement
approach procedures ... the aeroplane shall not be required to
be in any configuration other than the final landing
configuration at any point after passing ...5nm” from the
threshold; this corresponds to approximately 1500ft aal.
17

Noise from Arriving Aircraft – An Industry Code of Practice
40. Therefore, if possible do not lower the landing gear earlier than
required to satisfy company requirements for a stabilised
approach. This would not normally be until passing or below
2000ft (aal) depending on aircraft type.
41. Operators should ensure that operating procedures encourage
the use of CDA techniques whenever possible especially in
preference to any descent followed by an extended level
segment. Pilots should comply with noise abatement
procedures detailed in flight-deck documentation.
42. In the interests of noise abatement, to minimise disturbance in
areas adjacent to the aerodrome commanders of aircraft are
encouraged to avoid the use of reverse thrust after landing,
consistent with the safe and practical operation of the aircraft,
for example by selecting reverse idle.
Training 
43. The NATS College of Air Traffic Control has introduced a
module that addresses the training issue for Student ATCOs
(Air Traffic Control Officers). During the initial weeks of their
Approach Radar course, Student ATCOs receive a presentation
on the principles and application of CDAs in the approach
environment. This is then put into practice on all subsequent
simulator training runs. This enables the student to be prepared
to apply the principles and application of CDA in the field.
44. As part of ongoing programmes within NATS, presentations are
given to operational staff on the benefits of CDAs. In addition,
the UK Sustainable Aviation Initiative commits signatories to
“completing a CDA outreach programme at all main airports by
end 2006”. This programme is aimed at Air Traffic Control staff
as well as airport and airline staff.
18

45. The major UK based airlines operating into the three London
airports routinely train their pilots in CDA techniques. This is
regarded as best practice and other airlines operating into the
airports are encouraged to introduce similar training initiatives. 
Operational Issues For Airports
46. Runway exit points should be designed and located to help
minimise the use of reverse thrust and runway occupancy
times thus reducing the likelihood of go-arounds.
47. Airports should, where practicable, consider evaluating the
costs and benefits of potential design enhancements, such as
displaced thresholds.
48. Successful CDA is significantly assisted by the installation of
an ILS or equivalent, so airports are encouraged to provide ILS
to all approaches where CDA is expected. When the ILS is
unserviceable or is not provided, the request to achieve CDA is
not negated. Consideration should be given to the
establishment of P-RNAV APVs (Approach procedures with
vertical guidance) as the primary back up to ILS/MLS failure in
preference to reliance on SRA, NDB or visual approaches. In
situations when the ILS/MLS is not available, which are rare, a
greater achievement of CDA is likely if P-RNAV APV
procedures are in place.
49. Regular and timely feedback to all parties involved is essential
for understanding and improving performance against this
Code. In particular, use of NTK systems to analyse CDA
performance will enable each airport company to monitor and
discuss progress with pilots and ATC representatives at the
Company's appropriate technical group (e.g. BAA Gatwick’s
Flight Operations Performance Committee). Each airport’s data
is available for referral to individual airlines, and is routinely
19

Noise from Arriving Aircraft – An Industry Code of Practice
sent to NATS, for their own internal review. Data on CDA
performance is considered at each airport's Consultative
Committee. Working groups of these committees currently
review monthly CDA performance data. This will continue for
the foreseeable future and input to these groups, reporting on
progress against this Code, will continue to be sought from
pilots and ATC.
Non-Operational Factors to Mitigate
Approach Noise

50. The Code of Practice review group identified the following
areas that could be considered in order to further mitigate
approach noise: 
• The approach procedures published in the UK AIP should
clearly state the fact that the 500 fpm rate of descent does
not apply below Transition Altitude. Consideration should
also be given to stating “Continuous Descent Approaches in
effect” on the ATIS to remind crews not familiar with the
London airports.
• Minimum joining altitudes for ILS approaches should be
kept under review. 
• Use of standardised approach procedures including P-RNAV
approaches should be evaluated for potential noise benefits,
bearing in mind safety and capacity issues.
• ATC should continue to evaluate optimum speeds for
intermediate and final approach.
• The industry should continue to evaluate the benefits of
steeper approaches in both the intermediate and final
stages of approach.
20

• Aircraft manufacturers should evaluate the feasibility of
designing aircraft and FMS systems in such a way as to
make it straightforward for the pilot to be able to set and
monitor progress against a CDA profile.
• Guidance should be available to ATC to assist them in
identifying accurately the predicted distance to run for
arriving aircraft.
51. All organisations involved in writing the Code (and other
organisations who are implementing it) are encouraged to
continue reporting progress in their respective Annual
Environmental Reports, or similar, and to exchange best
practice with other organisations around the world.
52. DfT and CAA are encouraged to continue to promote and
disseminate, through their regulatory functions and through
participation in ICAO and other international fora, the use of
CDA where feasible at airports in the UK and abroad.
53. Further reviews of the Code will be undertaken when
considered necessary.
54. ‘The Future of Air Transport White Paper’, published in
December 2003 set out a plan for delivery of increased
capacity to cope with future demand (see box). 
Environment in the Air Transport White Paper
Chapter 12 of The Future of Air Transport White Paper states
that ‘environmental impacts must be taken into account
when increases in airspace capacity are made to allow
effective use of the additional airport capacity that would
result from the White Paper's proposals’.

55. In order to respond to these challenges, NATS may need to
redesign airspace in the London TMA. In doing so NATS will
21

Noise from Arriving Aircraft – An Industry Code of Practice
take into account a number of requirements set out by DfT and
CAA/DAP (see box below).
56. Any such revisions may need to take into account positioning
of holding patterns, standard arrival routes as well as standard
instrument departure routes (due to the interaction of arriving
and departing traffic in the London TMA).
Environmental Considerations in Airspace Design
DfT issued ‘Guidance to the Civil Aviation Authority on
Environmental Objectives Relating to the Exercise of its Air
Navigation Functions’ in 2002. Under section 70(2)(d) of the
Transport Act 2000 the CAA is required to take account of
any such guidance in carrying out its air navigation functions.

Section E (paragraphs 47 to 50) of the 2002 guidance deals
with factors relevant to arriving aircraft. 

Paragraph 48 states: 
‘The Government's aim is that radar manoeuvring areas and
the positions of stacks are designed and managed in ways
that will assist and promote the consistent use of
“continuous descent approach” (CDA) and “low power/low
drag” (LP/LD) operating procedures.’

Paragraphs 49 and 50 state: 
‘the CAA’s Directorate of Airspace Policy (DAP) should
ensure that consideration is given to how the use of CDA
and LP/LD procedures can be promoted in the course of
developing new procedures and when considering proposals
for changes to existing airspace arrangements. Both
procedures should be regarded as “best practice” for use at
all airports where local circumstances (such as terrain
clearance) do not preclude it. The procedures also reduce
fuel consumption and emissions.’

22

57. In a complex TMA environment, safety and operational
efficiency are key factors in airspace design. These factors
need to be optimised with the environmental impact of the
proposed operations. In accordance with the guidance to the
CAA and to proposers of airspace change, the design of
airspace to enable CDA operations is core to the design
process.
58. Mindful of the need to optimise the environmental performance
of airspace designs where possible, NATS has implemented an
environmental assessment process that enables the analysis of
noise, emissions and population exposure for airspace design
options. This analysis capability will form an integral part of the
ongoing airspace design work NATS undertakes in response to
the challenges set out in the Air Transport White Paper.
Other factors
59. External factors can mean that achievement of CDA is more
difficult in certain circumstances, for example periods of
adverse weather or aircraft emergencies. The review document
highlighted seasonal variations in CDA achievement, with
achievement in winter months typically lower than in summer.
The reasons for this variation are unclear at present but will be
subject to further review. 
60. Positioning flights between airports in and around the London
TMA are usually flown at altitudes below 6000ft. Such flights
will be registered by the NTK system as non-CDA approaches.
There are, however, relatively few of these movements. It is
also recognised and accepted that it is not practical to instruct
go-arounds to climb to an altitude of 6000ft, and therefore
these will register as non-CDA on subsequent re-approach to
the airfield. Again these are relatively few in number.
23

Noise from Arriving Aircraft – An Industry Code of Practice
Successes 
61. In compiling the first edition of the Code of Practice early in
2002, a number of initiatives were identified and implemented
that have led to an increase in the number of flights using CDA
techniques, ultimately resulting in aircraft remaining higher for
longer. Some of the successes are outlined below. 
62. The phraseology used by ATC to permit aircraft to descend on
the glidepath was reviewed and this has to some extent
reduced the need for level segments to be flown as aircraft join
the ILS. 
63. There has been clarification in the AIP of the applicability of the
500fpm minimum ROD requirement, removing a potential
source of confusion.
64. In the first edition of the code, it was strongly recommended
that typical approach paths from each holding stack be
published to enable pilots of suitably equipped aircraft to use
the automatic vertical guidance features of the autopilot to
improve CDA achievement, when operating in a radar vectored
environment. Initial Approach Procedures showing flight paths
from the holding stacks to the ILS intercept points have been
published in the UK AIP. Approximate distances to touchdown
are indicated on the Heathrow procedure diagrams to assist
pilots in achieving a CDA.
65. There is now an increased emphasis on training of pilots and
ATCOs with regard to arrivals noise mitigation.
66. The Code of Practice has raised the profile of arrivals noise
mitigation and in particular CDA worldwide, and has sparked
further work in the UK and internationally which is continuing,
involving various sectors of the aviation industry. Some
examples of initiatives with which representatives of the
24

Arrivals Code of Practice group have been involved are; 
• Key Stakeholders in the Eurocontrol CDA focus group
• Advice and guidance on implementation of CDAs at UK and
European International airports
• Input to a US-funded, NASA/Boeing run CDA arrivals study
at Louisville, Kentucky airport
• Advice and guidance to Cambridge University on the Silent
Aircraft Initiative
67. CDA performance has improved since the introduction of the
first edition of the Code of Practice. Figures 7 and 8 show the
increases in overall achievement of CDA across the three
designated London airports. It can be seen that in the night
quota period (2330-0600) a 13% increase in the use of CDA
has been achieved against a 5% growth in the number of
arrivals movements. An increase of 9% is evident in the Day +
night shoulder period (0601-2329) against a growth in arrivals
movements at 6.5%.
25

Noise from Arriving Aircraft – An Industry Code of Practice
Figure 7: CDA Achievement Night Quota Period
(2330-0600) at Designated London Airports

90%
A
80%
D
C
t
n
e
c
r
e
P

70%
60%
2001
2002
2003
2004
2005
2006
to July
Year
Figure 8: CDA Achievement Day + Night Shoulder Period
(0601-2329) at Designated London Airports

90%
A
80%
D
C
t
n
e
c
r
e
P

70%
60%
2001
2002
2003
2004
2005
2006
to July
Year 
Note: figures do not include arrivals to Stansted runway 05
26

68. In addition to the traditional CDA more sophisticated
techniques have been developed, often referred to as
Advanced CDAs. These call for the vertical profile to be an
integrated part of published arrival procedures.
69. The vertical profile is specified by means of Flight Level or
Altitude constraints at waypoints that are used to define the
procedure. The waypoints specify the lateral profile, whilst the
constraints published at the waypoints specify the vertical
profile, and the speed profile, if applicable.
70. The procedure is designed with the intention that it is flown
using an automated method of operation, whereby the avionics
interpret the coded procedure and calculate the optimum
vertical profile given the constraints published at the
waypoints.
71. Advanced CDAs have been on trial at both Heathrow and
Gatwick during recent years. The Heathrow trial has only been
available to traffic arriving from the East during the night
period. The current trial procedures include a CDA that
commences at 25,000 feet and terminates at the point of ILS
intercept.
72. The Gatwick trial is available on a 24-hour basis during times
of quiet traffic. At present, due to variability in the way in
which different avionics platforms interpret the speed profiles, it
is necessary to provide increased spacing requirements
between successive aircraft. This would result in a capacity
decrease during busy times. The Advanced CDAs are therefore
not utilised during busy traffic, when radar vectors continue to
be used.
27

Noise from Arriving Aircraft – An Industry Code of Practice
73. Procedures providing the vertical profile, enabling a CDA, are
based on Precision Area Navigation (P-RNAV). This technology
also permits the flexible placement of routes, enabling the
avoidance of noise sensitive areas.
74. It is anticipated that the trial procedures will become
permanent in due course. Dialogue with the ATS regulators is
currently underway to determine the process to be followed in
order to introduce these procedures on a permanent basis.
28

Arrivals Code of Practice Group Membership
BAA Gatwick
BAA Heathrow
BAA Stansted
British Airways
CAA, Directorate of Airspace Policy
CAA, Environmental Research and Consultancy Department
DfT, Aviation Environmental Division
EasyJet 
My Travel 
NATS
Virgin Atlantic
Useful Arrivals Noise weblinks
www.dft.gov.uk
www.airbus.com
www.ba.com
www.baa.com
www.boeing.com
www.caa.co.uk/dap/environment
www.cambridge-mit.org
www.eurocontrol.int
www.icao.int
www.nats.co.uk
www.sustainableaviation.co.uk
29

Noise from Arriving Aircraft – An Industry Code of Practice
References
Noise from Arriving Aircraft; Final Report of the ANMAC Technical
Working Group Dec 1999 DETR
Noise From Arriving Aircraft; First Progress Review
The Future of Air Transport – White Paper; December 2003
UK Aeronautical Information Publication
ICAO Circular 303: Operational opportunities for minimising fuel
burn
ICAO Document 8168 Vol I and II: Procedures for Air Navigation
Services: Operations (PANS-OPS)
30

GLOSSARY OF TERMS
Note that in some cases a simplified, more descriptive explanation
of terms is given here, rather than the “official” technical definition,
in order to assist the lay reader better to understand the terms
used.
aal
Aircraft height above aerodrome level (runway
datum).
AIP
UK Aeronautical Information Publication; colloquially
known as the ‘Air Pilot’, published by the Civil
Aviation Authority.
Altitude
The vertical displacement of an aircraft measured
above mean sea level (the altimeter pressure setting
is known as QNH). NB all ATC radar vectoring
operations below the minimum stack level are
conducted with reference to altitude. Most aircraft
operators use altitude throughout the approach.
ANMAC
DfT’s Aircraft Noise Monitoring Advisory Committee.
ATC
Air Traffic Control.
ATCOs
Air Traffic Control Officers.
ATIS
Aerodrome Terminal Information Service.
CAA
Civil Aviation Authority.
CAT II
An approach in visibility less than 550m runway
visual range.
CAT III
An approach in visibility less than 200m runway
visual range.
31

Noise from Arriving Aircraft – An Industry Code of Practice
Category C & ICAO PANS-OPS (Doc 8168) Speed Related aircraft
Category D
Category: Aircraft are divided into five speed
categories. These are based on a nominal threshold
speed defined as 1.3 times the stalling speed in the
landing configuration at Maximum Certified Landing
Weight. The five categories are:
A – <91 kts (e.g. DHC 6 Twin Otter)
B – 91 kts < 120 kts (e.g. ATR 42/72, BAe 146,
Fokker 50/100)
C – 121 kts to 140 kts (B737, A320, B757)
D – 141 kts to 165 kts (B777, B747, A340, MD11)
E – >165 kts. (no current civil aircraft type examples)
CDA
Continuous Descent Approach.
dB
Decibel, a unit used for quantifying sound level,
calculated as 10 times the logarithm (base 10) of a
sound energy ratio.
dBA
dBA is used to denote levels of sound measured on
a decibel scale using a frequency weighting that
approximates the characteristics of human hearing.
These are referred to as A-weighted sound levels;
they are widely used for noise assessment purposes.
Designated 
Heathrow, Gatwick and Stansted – these airports 
London 
have been ‘designated’ by the Secretary of State 
Airports
under Section 78 of the Civil Aviation Act 1982,
leading to the DfT taking responsibility for policy on
most aspects of airport noise.
DfT
Department for Transport.
DME
Distance Measuring Equipment.
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DTLR
Department of Transport, Local Government and
the Regions.
ERCD
Environment Research and Consultancy Department,
CAA.
Eurocontrol
European Organisation for the Safety of Air
Navigation.
FLCH
Flight Level Change – a control logic with set thrust
and the aircraft speed controlled by the elevator.
Flight Level
A surface of constant atmosphere pressure, which is
related to a specific pressure datum, 1013.2mb and
is separated from other surfaces by specific pressure
intervals (ICAO).
FMC/FMGC
Flight Management Computer/Flight Management
Guidance Control.
FMS
Flight Management System.
fpm
feet per minute.
Glideslope
The ILS vertical guidance, set at the London airports
for a nominal 3° descent angle.
Height
The vertical displacement of an aircraft measured
above a specified datum, normally the elevation of
an aerodrome (aal) (the altimeter pressure setting is
known as QFE) or above ground level (agl). In this
Code all heights are aal.
ICAO
International Civil Aviation Organization.
ILS
Instrument Landing System.
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Noise from Arriving Aircraft – An Industry Code of Practice
Initial 
Technical terms used in Instrument Approach 
Approach 
procedure design and related to obstacle clearance 
and 
requirements. The Intermediate Approach segment 
Intermediate  blends the Initial Approach into the Final Approach 
Approach
and is normally aligned with, or not more than 30°
offset from, the final approach track. For the
purposes of this Code, both relate to the parts of the
approach where radar directed marshalling and
sequencing of traffic takes place between the
Terminal Holding Point and the lowest (obstacle
clearance) altitude at which an aircraft must be fully
established on both the Localiser and the Glideslope
(2500 ft at Heathrow and Stansted, and at Gatwick
3000 ft for runway 08R and 2000 ft for runway 26L).
Localiser
The ILS azimuth guidance, coinciding with the
extended runway centreline.
LP/LD
Lower Power Low Drag approach procedure.
MLS
Microwave Landing System.
Nautical 
A distance defined by 1 minute of arc at the Equator,
Mile (nm)
equal to 6076 ft (i.e. 1.151 statute miles, or 1.852 km).
NDB
Non-Directional Beacon.
NTK
Noise and Track Keeping monitoring system; this is a
system that integrates noise data from a number of
microphones, the airport’s Flight Information System,
and the NATS Secondary Surveillance Radar and
flight identification. Heathrow, Gatwick and Stansted
each have similar systems, as does ERCD (which
receives data from the three airports’ systems).
Open 
A control logic with idle thrust and the aircraft speed 
descent
controlled by the elevator.
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PANS-OPS
ICAO Procedures for Air Navigation Services:
Operations.
P-RNAV
Precision Area Navigation.
QFE
Atmospheric pressure at aerodrome level (or at
runway threshold) (i.e. the altimeter reads zero feet
on the ground).
QNH
Altimeter sub-scale setting to obtain airfield elevation
when on the ground (i.e. the altimeter reads the
aircraft’s altitude Above Mean Sea Level).
ROD
Rate of descent.
SEL
The single event Sound Exposure Level is the sound
level in dBA which, if maintained for a period of one
second, would cause the same A–weighted sound
energy to be received as is actually received from a
given sound event.
SRA
Surveillance Radar Approach.
STAR
Standard Arrival Route.
TMA
Terminal Manoeuvring Area.
Transition
The altitude at or below which the vertical position of
Altitude
an aircraft is normally controlled by reference to
altitude.
VNAV
Vertical Navigation.
35

Noise from Arriving Aircraft – An Industry Code of Practice
Key Messages
1. Use of Continuous Descent Approach (CDA) is
encouraged wherever possible to realise the benefits of
reduced noise, fuel burn and emissions.

2.  From Transition Altitude, an arrival containing no level
flight or one phase of level flight not longer than 2.5nm is
classified as a CDA.

3.  The minimum rate of descent of 500fpm does not apply
below Transition Altitude. Airlines should ensure that
ROD requirements are refreshed during line training.

4.  Database suppliers should be encouraged to understand
the Code and ensure that the CDA requirements are
included on noise abatement pages.

5.  The industry and regulators should keep the possibility of
steeper glideslope capability under consideration in the
design of new generation aircraft. 

6.  Advances in technology which would provide key
information in relation to CDA achievement should be
kept under consideration.

7.  Operators should review their Standard Operating
Procedures regarding lowering of landing gear and flaps
to minimise drag and noise on arrival.

8.  Airports should consider the benefits, costs and practical
implications of introducing displaced thresholds. 
9. The industry shall continually seek opportunities to
improve the arrival procedures in order to minimise the
environmental impact. Any new initiatives to reduce
noise must take account of the impact on air quality.
CDA is win-win!  

10. A CDA means HIGHER FOR LONGER!
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