Noise Research

Optimized Profile Descent

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Optimized Profile Descent (OPD) is a cockpit based flight technique that involves the continuous, gradual descent of aircraft on a constant slope at idle or at minimal low power settings.

Airframe noise is reduced by the delayed deployment of flaps and landing gear until established on final approach. Instead of using the normal step down arrival procedure, the with an OPD the pilot flies a constant descent angle to the runway with engines at idle power as long as possible. This can conserve fuel, limit emissions, and reduce noise during the descent when the airplane is closer to the ground. Minimal power-ups and level-offs may be required to manage speed and when preparing the aircraft for final approach. At 1,000 feet, the aircraft's power is again engaged to land the craft. When permitted by the air traffic control tower, OPD will be used. For more details, see the Optimized Profile Descent Procedure.

Optimized Profile Descent Procedure

One of the major sources of disturbance in and around airports is noise produced by aircraft landings. The OPD is a not a new technique. Pilots use this minimum power and OPD technique whenever possible to airplanes achieve fuel efficiency and quieter landings. It improves upon standard landing procedures in two ways:

Aircraft fly at higher altitudes for longer periods of time so that less noise reaches the ground.

The optimal landing paths require less work from the aircraft's engine, so the engine produces less noise. Standard air traffic control procedures may require aircraft landings to follow a stair-step flight path to preclude conflicts with other operations. An aircraft descends until it reaches a specified altitude and speed. It then levels off and flies at a constant speed. The aircraft may repeat this procedure multiple times before reaching the ground.

Using published ATC flight procedures designed with an Optimized Profile Descent, the stair step path may be eliminated when possible and aircraft never maintains constant speed or altitude once it begins descent. Using the Optimized Profile Descent technique on published flight procedures with an optimized descent profile allows an aircraft to stay at higher altitudes for longer periods of time. In addition, it requires less work from the engine than standard landing procedures. (Extra work is needed for a descending airplane to level off.)

These two results help to reduce aircraft landing noise by 3 to 6.5 decibels on the ground near the airport. This is a noticeable decrease in sound level. The continuous descent arrival also reduces an airplane's fuel use by about 200 kilograms.

Why Isn't Optimized Profile Descent Used for All Landings at All Airports?

While this approach sounds simple, it is not easy to apply. In heavy traffic, air traffic controllers use periods of constant altitude and speed to manage how far an airplane is from the airport and other airplanes. The continuous descent arrival technique does not allow air traffic controllers to use this technique. While information about an airplane and its flight path can be gathered in other ways, these methods are often less effective.

For example, controllers have access to radar information including lateral position information for the aircraft and runway, groundspeed, and altitude of the aircraft. However, due to the rotation rate of the radar, controllers are usually provided with only one set of readings every 4.8 seconds. Because of these limitations, the optimized profile descent may not always be performed properly.

In some situations, the required separation distances between airplanes would not be maintained if the aircraft were allowed to continue on their flight paths toward the airport. Therefore, an air traffic controller may require an aircraft to level off and follow a standard landing pattern or command the aircraft to perform a go-around. These correction techniques increase the noise reaching the community, counteracting the intended benefits of the continuous descent approach.

Where is the Optimized Profile Descent Used?....

Despite potential problems in heavy traffic, the optimized profile descent procedures enabling a optimized profile descent are suitable for medium to light traffic. Because of its success, the optimized profile descent is used at a number of airports such as Gatwick Airport (located 28 miles from London) and Heathrow Airport (located 15 miles from London). Tests have also been conducted, with favorable results, at Louisville Airport in Kentucky.

References:

Marks, Paul. "Smooth Aircraft Approach Cuts Noise Pollution." NewScientist.com. 24 November 2003. 29 October 2006.

Reynolds, Hayley J. Davison, Tom G. Reynolds and R. John Hansman. "Human Factors Implications of Continuous Descent Approach Procedures For Noise Abatement in Air Traffic Control." 6th USA/Europe Air Traffic Management R&D Seminar, Baltimore, USA, June 27-30, 2005. 29 October 2006.

Scanlon, Lisa. "Quiet Landing: John-Paul Clarke's new procedure could help reduce the noise from landing airplanes and bring relief to millions." Technology Review. 2004. 29 October 2006.

"London Heathrow." AirWise. 2006. 4 November 2006.

Fact Sheet – NextGen and Performance-Based Navigation

Glossary Words:

air traffic control, altitude, decibel, groundspeed, noise, runway, separation, sound level

For definitions of words used in this section go to the NoiseQuest Glossary of Terms.