WHO aircraft noise guidelines explained: 45 dB Lden and 40 dB Lnight

In 2018 the World Health Organization's office for Europe published new guidelines on environmental noise, built on eight systematic reviews of the research. For aircraft they are the strictest of any source: below 45 dB Lden on average and below 40 dB Lnight at night. This guide explains what the two numbers mean, how they were chosen, how firm they are, and how they compare with the levels governments actually use.

What the WHO recommends

For aircraft the WHO makes three recommendations, all rated strong:

• Average exposure: keep aircraft noise below 45 dB Lden, because above that level it is linked with harm to health.
• Night exposure: keep aircraft noise below 40 dB Lnight, because above that level it is linked with disturbed sleep.
• Action: where people are exposed above those levels, governments should take suitable measures to reduce the noise, including changes to infrastructure such as runways and flight paths.

Both levels are calculated or measured outdoors, at the most exposed wall of the home, as a long-term average, usually over a year. Lden is the average over 24 hours with 5 dB added to evening noise (19:00-23:00) and 10 dB to night noise (23:00-07:00), to reflect how much more it bothers people then. Lnight is the plain average from 23:00 to 07:00. Our guide to Lden, DNL and Lnight explains these measures in more detail.

Aircraft get the lowest levels of any transport source:

The main reason is that, at the same average level, aircraft noise annoys more people than road or rail traffic. The 2018 guidelines replace the WHO's community noise guidelines of 1999 and sit alongside its night noise guidelines of 2009, which set 40 dB Lnight for all sources with 55 dB as an interim target.

How the two numbers were chosen

The WHO's panel picked the health effects that matter most and, for each one, a "relevant" increase in risk. It then read off the noise level at which each increase is reached:

• Annoyance: 10% of people highly annoyed, reached at 45.4 dB Lden. Highly annoyed means answering at the top of a standard survey scale, "very" or "extremely" annoyed.
• Coronary heart disease: a 5% rise in risk, reached at 52.6 dB Lden. The studies found 9% more of it for each 10 dB.
• Children's reading: a one-month delay, reached at 55 dB Lden.
• High blood pressure: the one study that qualified found no clear rise in risk.

Annoyance gave the lowest level, and the panel judged that below it there was probably no relevant rise in the other risks, so 45.4 dB was rounded to 45 dB Lden.

For the night, the benchmark was stricter: no more than 3% of people highly sleep-disturbed. But the surveys of aircraft noise only had reliable data from 40 dB Lnight upwards, and at 40 dB about 11% were already highly sleep-disturbed. Rather than extrapolate below the data, the panel set 40 dB. It said openly that this level may not fully protect health, and that anything lower would probably mean banning night or early-morning flights altogether.

The curves behind the two numbers, from the WHO's reviews:

How strong the evidence is

A strong recommendation, in the WHO's terms, is one that can be adopted as policy in most situations. The panel rated the two levels strong because the evidence on annoyance and sleep was of moderate quality. It rated the call for action strong because studies of runway openings, closures and new flight paths showed that changing the noise changes how many people are annoyed.

The ratings for each effect:

So the 45 dB level rests on annoyance, the best-studied effect, not on heart disease. What the research says about each effect is in is living near an airport bad for your health?

The annoyance curve has its critics. In a 2018 paper, Truls Gjestland argued that the studies chosen were not representative of people living around airports and that some did not follow standard methods. The review's authors rejected most of his critique in 2019. National surveys published since then fall around the WHO's curve: the FAA's survey found 15-23% highly annoyed at 50 dB DNL, and the UK's 2023-24 survey found 12.6% at 50 dB Lden, where the WHO's curve gives 18%.

How the WHO levels compare with the rules governments use

In the EU, the Environmental Noise Directive sets no limits. Airports with more than 50,000 flights a year must be mapped every five years, from 55 dB Lden and 50 dB Lnight. In the 2022 round, 2.4 million people were above 55 dB Lden from aircraft and 0.7 million above 50 dB Lnight. EASA estimates that at the WHO levels those figures rise to 14.9 million and 5.3 million. Since 2020, the directive has also set out how to estimate the number of people highly annoyed, highly sleep-disturbed or at risk of heart disease, a method revised after the latest review of the health evidence.

In the UK, the lowest observed adverse effect levels are 51 dB LAeq,16h by day and 45 dB LAeq,8h at night, under the air navigation guidance in force from 1 October 2026. These are averages over the 92 summer days without an evening penalty, so they are not directly comparable with Lden. The UK's own recent surveys found effects at or below those levels: 1 in 10 highly annoyed at about 43 dB LAeq,16h in the CAA's survey, and 1 in 10 highly sleep-disturbed at 44 dB LAeq,8h (43 dB Lnight) in the ANNE study.

In the US, the FAA treats 65 dB DNL as the threshold for significant exposure and for homes being compatible with an airport. DNL is a 24-hour average with 10 dB added from 22:00 to 07:00 and no evening penalty, so it is roughly comparable with Lden. At 65 dB it is 20 dB above the WHO level: 100 times the sound energy, and about four times as loud. The FAA's 2021 survey found 60-71% of people highly annoyed at 65 dB DNL. Its noise policy review has not changed the threshold.

Why an average only tells part of the story

Lden and Lnight turn a year of planes into one number. The WHO itself notes that averages may hide effects such as awakenings, and that measures based on the number of loud events may suit them better, though such measures are not widely used.

The UK's ANNE study shows why counts matter. It found 1 in 10 people highly sleep-disturbed where somewhere between 5 and 20 planes on an average summer night were louder than 60 dB outside. How that plays out at night is covered in aircraft noise and sleep.

How to find out whether a home is above the WHO levels

Few homes have an official figure at the WHO levels, because official maps start higher. What you can do:

1. Check the official noise map. If the home is inside the 55 dB Lden band of an EU strategic noise map, it is at least 10 dB above the WHO's level; inside the 50 dB Lnight band, the same at night. The UK's contours start at 51 dB LAeq,16h and 45 dB LAeq,8h. In the US, the level that counts for FAA policy is 65 dB DNL, 20 dB above the WHO's. Our guide to official airport noise maps explains how to read them.
2. Don't read "outside the map" as "below the WHO level". EASA's figures suggest about six times as many people in Europe are above 45 dB Lden as are inside the 55 dB band.
3. Count the loud planes, by day and at night. Look at the number of flights between 23:00 and 07:00, and when the first ones arrive, on typical days in each runway direction.

A Flight Noise report does the counting for one address: every loud plane from the last twelve months of recorded flights, by day and at night, with real days replayed.