Approach routes are defined as segments – straight or arc of circles – each with a minimal altitude. The steps can be of various length and the descents have various slopes. The design of procedures is influenced by three main factors:

• Obstacles
• Airspace design – keep departures and arrivals apart
• Noise sensitive area

As long as the prescribed altitudes are respected, the management of descent is left to the crew. If your pilot think it’s fun to crash-dive, then push the throttles to stop the steep descent and finally fly low for miles, that’s his choice, but at least four categories of people won’t like it…

• Passengers won’t like the steep descent and aggressive level-off
• Airline managers will hate paying for fuel wasted to stop the descent
• Environmentalists will complain about the additional pollution
• Neighbors will be disgusted by this plane flying low over their place

The airline manager will certainly be the one with most influence on the pilot ! As good pilots will also care for the three other factors, most of them try to fly continuous descents which are economical (low power), enviroment friendly (low consumption), less noisy because of less power and airplane is always higher or at minimal altitude, and more comfortble for passengers.

If I was a marketing / management guy I would call it a win-win-win-win situation. However this is not always possible, mainly for traffic seperation purposes. The idea is to have departing aircraft (extremely noisy) climbing as quick as possible, and direct arriving traffic below departures. This sometimes force procedure designers to plan long level segments which can not be flown on low power.

With the advances of modern navigation (GPS, inertial and multi DME), planes no longer have to fly from beacon to beacon, allowing for more freedom in approach design. With so-called “Continuous Descent Approaches (CDA)”, a continuous descent is no longer an option for the pilot, they are designed so ! CDA are nothing else than long descents, some starting as high as 15′000 feet.

They can not always be flown at IDLE power because all airctafts don’t have the same performance, wind influence and traffic, but where such approaches are available they help reducing fuel consumption, noise and impact and environment.

The UK Civil Aviation Authority published this leaflet about CDAs. You can also check this page about noise on British Airways website.

This post is the fourth in a series about how modern planes are designed and operated with maximal care to the enviroment. The first one was about Jet-A1 engines, and the second about composite materials and Computer Aided Design and the thrid about electrically powered planes.