Firms unveil quieter jet engines

The bombardier aircraft CS series is one of the most quiet aeroplanes. AFP 

By DANIEL ONDIEKI
inShare

Aeroplanes are very noisy. The miracle of flight seems predicated on the generation of extreme amounts of noise. Most of this noise comes from the engines with a contribution from the sound from the airflow around the fuselage.

An observer standing a 100 feet from a jet engine producing take off power would experience 140 Db (Decibels) of sound. Since the decibel scale is logarithmic, this means that this is a trillion times louder than a normal conversation of 40 dB.

The issue of noise is more than having to turn up the volume on your TV or talking slightly louder in a conversation. Scientists have known for a while that noise is harmful to our health. Apart from the obvious hearing loss, there is an increased incidence of heart attacks, lower cognitive performance and poor sleep.

I happen to live nine kilometres from the airport which is reasonably far. Yet at night or in the early mornings I can sometimes make out the faint roar of a jet engine from a plane taking off.

Since the intensity of sound decreases proportionally with the square of the distance from the source, you can imagine what the people living around the airport experience.

For this reason in many countries, communities that live around airports have been able to exert pressure and extract concessions from authorities as concerns noise. The number of night landings is limited and older noisy aircraft have been banned from certain airports.

Each newer generation of airliners has been quieter than their predecessors. On a recent demonstration flight, the new Bombardier CSeries plane almost took off without the assembled phalanx of journalists and employees noticing because of its quietness.

On takeoff airplanes climb higher before levelling off to put more distance between them and the ground. Planes can also take paths that avoid high population areas.

Steep fines and noise monitors installed along takeoff and landing paths encourage airlines to stick to the prescribed noise abatement rules.

When it comes to landing though, the planes are much more restricted since safety rules require that the plane to be aligned to the runway from a long distance.

In addition the instrument landing system which most planes use on final approach is a straight beam. Short of changing runways, people living underneath this beam can expect planes to fly over their houses every day.

It’s here that we may have a slight advantage. Most of our final approach takes place over the Nairobi National Park whose inhabitants are in no position to complain.

 

For takeoff, the people of Utawala have got a weak case. They found the airport there and as it expands they are likely to find their already dire situation getting worse. In time they may also start pushing back against night takeoffs.

Despite all the environmental noise pollution, modern subsonic jet planes are surprisingly silent inside.

So much so that flight crew are not really covered by occupational health guidelines on sound exposure. However, if you require quieter surroundings to sleep, some noise cancellation earphones or ear plugs should do.