What to Do About Noise?

 

Optimized Profile Descent (OPD) is a descent profile that starts at Top of Descent and, to the extent possible, comprises idle power descents that minimize thrust required to remain on the vertical path. OPD flight procedures use the capabilities of the aircraft FMS to fly a continuous descent profile minimizing level-off segments, based on the actual performance of the aircraft under current flight conditions along a fixed lateral path. The termination point of an OPD may be on an arrival procedure such as a published Standard Arrival Route (STAR) or at a point in space that allows for radar vectoring.

OPDs are designed to allow use of aircraft automation and piloting techniques to maximize fuel efficiency and minimize environmental impact. Instead of using a typical step down arrival procedure, with an OPD the aircraft flies a constant descent profile with engines at idle power and minimal thrust requirements. This can conserve fuel, limit emissions, and reduce noise. For more details, see the discussion on Optimized Profile Descent Procedures in the next section.

Optimized Profile Descent Procedures

One environmental concern in and around airports is noise produced by aircraftby aircraft. The flight techniques utilized during an Optimized Profile Descent are not new. Pilots use minimum power and optimal glide angle techniques whenever possible to achieve fuel efficiency and quieter landings. OPDs take advantage of these techniques to improve upon standard landing procedures in two ways:

Aircraft fly at higher altitudes for longer periods of time reducing the amount of noise exposure on the ground.

An optimal descent profile requires less work from the aircraft's engine, as a result the engine produces less noise. Non-OPD air traffic control procedures may require arriving aircraft to follow a step-down flight path to resolve conflicts with other operations. During a traditional step-down procedure 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 landing.

Using an Optimized Profile Descent, the step-down flight path can be eliminated when possible and, in doing so, an aircraft may not be required to level off once it begins its descent. This allows an aircraft to stay at higher altitudes for a longer period of time. In addition, it requires less work from the engine than traditional arrival procedures. (Extra work is needed for a descending aircraft to level off.)

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

While this approach sounds simple, it is not easy to apply. Air traffic controllers visually scan a radar display to assess aircraft altitude and speed in order to approximate how far an aircraft is from the airport and other aircraft. The continuous descent approach does not allow air traffic controllers to use this technique. While altitude, speed and other information about a specific aircraft can be gathered in other ways, this information, due to the rotation rate of a radar antenna, is only updated every 4.8 seconds. Because of these limitations, the continuous descent approach cannot always be flown completely. In some situations, the required separation between aircraft cannot be maintained if the aircraft were allowed to continue on their flight paths toward the airport. Therefore, an air traffic controller may issue a level-off altitude, a speed restriction or instruct the pilot to execute a go-around. These correction techniques may increase the noise exposure of the community, counteracting the intended benefits of the continuous descent approach.

When is the Optimized Profile Descent Used?

Due to the issues that could arise during heavy traffic, Optimized Profile Descents are best suited for use during periods of medium to light traffic.

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 [[CommunityTools.Glossary#noise | 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 (ATC), altitude, decibels, ground speed, noise, runway, separation, sound level

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