Some after a hard day at work, you have just fallen into a deep sleep. Suddenly, there is a mighty roar, the windows rattle and the building shakes. You are rudely woken up by a jet taking off from Kathmandu airport. You toss and turn fitfully all night and are a wreck at work the next morning.
As Kathmandu airport is swamped by urban sprawl, more and more families are forced to live directly under the flight path of aircrafts landing and taking off.
So far, the capital's citizens have been mainly worried about air and water pollution. But increasingly, noise from street traffic and aircraft are becoming a concern. Noise pollution can be of two types: a single unprotected short-range exposure that can cause permanent hearing loss, or long-term exposure to less intense sounds. Both are harmful to health.
It is exposure to longterm noise at night that has causes indirect harm because of sleep deprivation. Most airports around the world have flight curfews at night and new airports are now being located on landfills out at sea.
Although advances in jet engine technology has reduced their noise in recent years, a twin-engine jet taking off still emits 150dBA directly under its flight path. Research has shown that is enough to disturb sleep, make the hair on the back of the neck stand up and raise blood pressure.
Kathmandu airport has a noise problem even in the daytime because of the Valley's bowl-shaped topography: this amplifies the sound and prolongs the echo. Planes also have to climb on maximum power to get over the surrounding mountains and options for standard departure that could avoid built-up areas are limited.
In addition, as winter approaches, poor visibility till noon means most flights are bunched up in the afternoon or night. The increase in flight frequency of low-flying military helicopters has made the problem worse. Most domestic carriers operate relatively quiet turbo-props and are not much of a nuisance. The biggest window rattlers are the F-28s operated by Bangladesh Biman. Although a small aircraft, it is powered by older model rear-mounted turbofans. Thankfully, it has an afternoon departure. 
However, the four-engine Airbus 340s operated by Austrian Airlines and its Friday morning 2AM takeoff is a sleep spoiler not just for those living near the airport but for people right across the Valley. The fully-tanked 340 on a nine-hour flight to Vienna has a slower rate of climb and makes two orbits over the airport before heading off. The flights have been suspended for the off season and are due to restart in mid-September. Royal Nepal Airlines' 757s are less noisy but become a major headache when schedules are disrupted and they take off at ungodly hours, waking everyone up.
"My son gets up every night, and this means loss of sleep for the whole family," says Uday Khanal, a physics teacher who lives in Baneswor. It is much worse for Bina Dhakal in Lokanthali who is directly under the flight path of jets taking off, and says she suffers from partial hearing loss due to longterm exposure to jet noise. Even as far away as Sanepa, residents complain that midnight takeoffs disturb their sleep.
It is difficult to quantify the cost of aircraft noise in dollars and cents. An Organisation for Economic Co-operation and Development (OECD) study six years ago identified four categories of impact from noise pollution: productivity losses due to poor concentration, communication difficulties or fatigue due to insufficient rest and health complications caused by lack of sleep. Aircraft noise also lowers real estate property value.
A study of Kathmandu conducted by Japan International Cooperation Agency (JICA ) back in 1989 had warned that air traffic growth at Kathmandu airport could present longterm noise hazard concerns. As residential areas grow around the airport and under the flight path, the problem is bound to get worse.
"We are aware of the problem, but there is sometimes no alternative but to have night flights," says BB Adhikari at the Civil Aviation Authority of Nepal (CAAN). Indeed, if a night curfew is imposed, Kathmandu airport would be open for only six hours in winter. Imposing a 'noise tax' on large planes taking off at night is also ruled out because Kathmandu's landing charges and handling fees are already one of the highest in the world.
"The present extent of the noise problem doesn't warrant investing in noise-monitoring equipment because it is too expensive," says Binod Gautam at CAAN. Privately, officials admit that there just isn't enough of a public outcry yet to warrant such expense.
True, the problem of the occasional noisy jet probably pales in comparison to other woes: the lack of water, garbage and traffic. But one thing is certain: Kathmandu's aircraft noise problem is bound to get worse before it gets better.
mrinmoy_m@SIFY.com
How loud is too loud?
Continued exposure to noise above 85dBA over time will cause hearing loss. To know if a sound is loud enough to damage your ears, it is important to know both the loudness level (measured in decibels, dBA) and the length of exposure to the sound. The harm grows exponentially. For example, the human ear can tolerate 85dBA for 8 hours before it gives up. At 110dBA, the maximum exposure time is 1 minute 29 seconds. Noise levels above 140dBA can cause damage to hearing after just one exposure, for example, to a bomb explosion.
The following are decibel levels (dBA) of common noise sources:
0 The softest sound a person can hear
10 Normal breathing
40 Quiet office, library
95 Traffic at Putali Sadak
120 Disco, thunderstorm
150 737-300 on take off at runway threshold
180 Rocket launch from pad
