Noise Abatement Procedures

Noise abatement procedures are the techniques, runway choices and routes that reduce the noise aircraft make over the people living around an aerodrome. They range from the thrust and flap schedule flown after take-off to the runway nominated for use at night, the track a departure follows between two villages, and the way an arrival descends. For the crew they are part of the published procedure for the aerodrome, flown like any other constraint.

The international framework is ICAO's PANS-OPS, Doc 8168, Volume I, which sets the aircraft operating procedures and the safety limits within which they apply. The State in which the aerodrome lies decides the noise abatement objectives there. The operator develops procedures for each aeroplane type, and the State of the operator approves them. The pilot flies them, but never at the expense of safety.

Purpose of noise abatement

Aircraft noise is a major environmental constraint on many aerodromes, and ICAO addresses it through a balanced approach with four elements:

1. Reduction of noise at source. Aircraft are noise-certificated under ICAO Annex 16, Volume I. Toulouse-Blagnac, for example, accepts turbofan aeroplanes with a maximum take-off mass of 34,000 kg or more, or more than 19 passenger seats, only if they meet the standards of its Chapter 3, 4 or 14.
2. Land-use planning and management, which keeps new housing away from the noisiest areas.
3. Noise abatement operational procedures, the subject of this article.
4. Operating restrictions, such as night-time bans on the noisiest types.

Enforcement can be real. French aerodrome entries warn that breaches of the local noise rules may be reported to ACNUSA, the airport noise authority, which can fine an operating company up to 40,000 euros. French visual approach charts also mark noise measurement areas around some aerodromes.

In Europe, CAT.OP.MPA.130 requires an operator to establish departure and arrival or approach procedures for each aeroplane type that take account of the need to minimise noise. The procedures must give safety priority over noise abatement and be simple to fly, without adding significantly to the crew's workload in critical phases of flight. In the United States, the FAA sets up formal runway use programmes at individual airports. Where one exists, 14 CFR 91.129(h) requires the pilot of a large or turbine-powered aeroplane to use the noise abatement runway ATC assigns. ATC may still assign a different runway if the pilot asks for one in the interest of safety.

Noise abatement departure procedures

A noise abatement departure procedure (NADP) manages thrust, speed and flap retraction during the climb to 3,000 ft above the aerodrome. PANS-OPS gives two, and EASA guidance (AMC1 CAT.OP.MPA.130) expects an operator to define both for each aeroplane type:

• NADP 1, the close-in procedure, reduces noise near the end of the runway.
• NADP 2, the distant procedure, reduces noise further along the departure path.

Both share the same safety floor. The noise abatement initiation point may not be below 800 ft (240 m) above aerodrome elevation, and up to that point the aeroplane climbs in its take-off configuration at a speed of at least V2 + 10 kt. Below 800 ft the priority is climb performance and obstacle clearance, and neither thrust nor configuration is changed for noise reasons.

The two procedures reflect a simple trade. NADP 1 keeps the flap out and the speed low, so the aeroplane climbs steeply and passes over nearby housing as high as possible. NADP 2 reaches the clean configuration early, so the aeroplane needs less thrust as it climbs away over communities further out. Which one an aerodrome asks for depends on where its neighbours live.

Aerodromes publish their choice in AIP AD 2.21. Toulouse-Blagnac requires the ICAO NADP 1 profile for turbofan departures from runways 32L and 32R, and Nice requires NADP 1 because its objective is close-in noise reduction. Where the aerodrome leaves the choice open, the operator's standard applies, and some operators make NADP 2 their default. On the A320 the thrust reduction and acceleration altitudes default to 1,500 ft, or to the airline's policy, and the crew adjust them on the PERF TAKE-OFF page to match the local procedure. A reduced-thrust take-off also lowers noise (see reduced and derated take-off thrust).

Noise preferential runways

A noise preferential runway is the runway nominated for noise reasons: typically the one whose departure and approach paths avoid built-up areas, or a runway used at night so that departures head out over the sea or open country. Using it may mean accepting a tailwind or a crosswind, so PANS-OPS limits how far noise may decide the choice. Noise should not be the determining factor in nominating a runway when:

• the runway is not clear and dry, for example because of snow, slush, ice or water
• the ceiling is below 500 ft or the visibility below 1,900 m
• the crosswind component, including gusts, exceeds 15 kt
• the tailwind component, including gusts, exceeds 5 kt
• windshear has been reported or forecast, or thunderstorms are expected to affect the approach or departure.

Even inside these limits, the pilot-in-command may refuse a runway that is unsuitable for the aircraft on the day and ask for another.

Noise preferential routes

A noise preferential route is a departure or arrival track, usually published as a SID or STAR, designed to keep aircraft away from noise-sensitive areas (see instrument departures). PANS-OPS protects the aircraft on such routes:

• Turns. A turn should not be required until the aircraft is at least 500 ft above the terrain and the highest obstacle under the flight path.
• Bank angle. Bank for turns after take-off is normally limited to 15°, unless the procedure allows enough speed for a steeper bank.

Aerodromes can make these tracks binding. At Toulouse-Blagnac, turbofan aircraft must overfly the first turning point of the SID unless ATC clears otherwise or there is an emergency. At Nice, departing aircraft may not overfly land below 6,000 ft above the surface unless ATC instructs otherwise. VFR pilots meet the same idea on visual approach charts. French charts mark built-up areas whose overflight must be avoided with a blue circle, and circuits are often drawn to pass around them. In the United States, pilots are requested to stay at least 2,000 ft above the surface over charted national parks, wildlife refuges and wilderness areas; over some designated areas, such as Grand Canyon National Park, federal statutes impose binding restrictions.

Continuous descent operations

On arrival, noise comes mainly from the thrust needed to overcome drag, so the quietest arrival is the cleanest one flown at low power. A continuous descent operation (CDO) is an arrival flown with as few level segments as possible, at low thrust and in a low-drag configuration for as long as practicable, ideally from the top of descent. It is also known as a continuous descent approach (CDA). Compared with a stepped descent with powered level-offs at low altitude, a CDO reduces noise, fuel burn and emissions. ICAO's guidance is its Continuous Descent Operations Manual (Doc 9931).

A CDO needs more than good technique. Doc 9931 stresses that airspace design, procedure design and ATC techniques must work together: the STARs must allow an uninterrupted descent, and crews need a reliable idea of the distance to go, so that the flight management system or the pilot can plan the descent to arrive at the right energy. Aerodromes may add specific instructions. At Toulouse-Blagnac, for instance, the AIP recommends avoiding increases in power or thrust on final approach, and requires instrument approaches to intercept the glide path no lower than 3,000 ft AMSL and to fly the final approach at the ILS glide path angle.

A CDO is not the same as the continuous descent final approach (CDFA). CDFA is a technique for flying the final segment of a non-precision approach without level-offs. A CDO concerns the whole arrival.

Safety limits on noise procedures

PANS-OPS surrounds noise abatement with limits designed to keep it from eroding safety margins:

• Departure. No noise abatement thrust or configuration change below 800 ft, and at least V2 + 10 kt up to the initiation point.
• Routes. No turn below 500 ft above terrain and obstacles, and bank normally limited to 15°.
• Approach. The aircraft may not be required to be in any configuration other than the final landing configuration after passing the outer marker or 5 NM from the threshold, whichever is earlier. Noise procedures may not require an approach angle steeper than 3°, or steeper than the published ILS glide path where that is higher.
• Runway selection. Noise gives way to the wind, visibility, ceiling, runway condition and weather limits listed above.

Beyond these, the commander keeps the final authority: a noise procedure is flown only when it is safe to fly it. If an engine fails after take-off, the crew fly the engine-out procedure for the runway instead of the noise abatement profile. If a noise preferential route leads into a building cumulonimbus or a heavy shower, the pilot deviates as far as necessary and tells ATC. No emergency needs to be declared for such a deviation, and none of these limits relieves the crew of terrain clearance, traffic separation and minimum altitudes.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.