Introduction

CAAN is often asked questions like: why are flights flying over my house, what happened to the nighttime curfew, why has the noise been louder the last few months, how is the noise measured and monitored, and what is DNL. To help our supporters and others who may be interested, we have compiled a list of facts, figures, and explanations to some of these questions.

Table of Contents (Click on subject of interest)

Metropolitan Washington Airports

National Airport

Dulles International

Operational Factors

Restricted areas

Aircraft Design

Population Affected by the Airports

Factors that Affect the Level of Noise

Noise Abatement procedures

Nighttime operations

Noise measurements

The 65 DNL Noise Threshold

Noise Monitoring

Noise Measurements for the Washington D.C. Area

Noise mitigation funding

Air emissions/Water pollution and its control

Helicopter activity

FAA Operations

FAA Responses to queries

Metropolitan Washington Council of Governments/APC

Metropolitan Washington Airports
National Airport (Amended 2/21/09)
Located - 4 1/2 miles south of Washington D.C.
Main runway is just 0.7 miles from Jefferson Davis Highway (US Rt 1)
Opened - June 16, 1941
Built by - the Federal Government
Size - covers 860 acres: 733-land, 127-water.
Runway Configuration - There are three intersecting runways at National:

• Runway 1/19 (length - 6,889 feet) [Multiplying the runway heading by 10 gives the magnetic compass reading of the runway; thus the "19" is translated as 190 degrees (due south) and the "1" as 10 degrees (due north)]
• Runway 15/33 (5,204 feet)
• Runway 4/22 (4,911 feet)

National Airport Runway Configuration

* 1L (left)/19R (Right) (11,500 feet)
* 1R/19L (11,500 feet)
* 12/30L (10,500 feet)
* 12/30R (10,500 feet)

Washington Dulles International Airport Runway Configuration

Additional facts about National and Dulles Airports and their operations may be viewed at the Metropolitan Washington Airports Authority website.

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Operational factors. At National, major air carriers "fly the river corridor"; that is, they fly up or down the Potomac River using the longest runway at National, runway 1/19. Sometimes aircraft take off to the north and land from the south. At other times it is the reverse. The reason for reversing the direction is that aircraft should always take off into the wind. Flying into the wind affords more lift and is therefore a safer way to operate. If the wind is less than 9 knots, however, FAA air controllers may elect to have aircraft take off even if there is a slight following wind. At National, this switching from north to south operations will be noticed by residents, and may happen several times a day.

Restricted areas
There are areas in the Federal part of Washington D.C. over which aircraft may not fly. These are called restricted areas. They are the:

- White House
- Capital
- Mall
- Vice President’s house at the Naval Observatory.

Aircraft design (revised 2/07). When reading the takeoff and landing noise levels stated in FAA documentation, it is easy to think that planes make more noise on landing that they do on takeoff. A Boeing 757, for instances, has a takeoff noise level of 72 dbA and a landing noise level of 85 dBA. The confusion comes from the fact that when the FAA certifies a plane's noise levels they place the noise meter micrphones at different locations. For takeoff the microphone is located about 4 miles from where the aircraft starts its takeoff (the so-called brake release point). By the time the aircraft passes over the microphone it has attained some altitude, perhaps 1500 to 2000 feet. For landings the microphone is only about 1.25 miles from the plane as it descends, and the aircraft is usually lower in altitude, maybe 400 feet. Also, when landing the plane has its flaps and landing gear down and these appendages create noise. It's referred to as flying in a "dirty" condition as opposed to the "clean" condition when taking off, wheels and flaps up. Hence, when landing the noise level figure is higher as in the example, 85 dBA. However, it is the takeoff that we hear the most noise. It's all in how one defines the reference points.

Initially, jet aircraft noise was not considered a problem as there were so few jets flying. Over the years, though, the Federal Government realized that noise was becoming a problem and required the manufacturers to decrease the level of noise emanating from the engines and airframe. First we had Stage 1 like the old Boeing 707, then Stage 2, epitimized by the Boeing 727, 737-100, the 747's, and the DC-9's. In 1990, the Federal Government mandated that all Stage 2 commercial aircraft over 75,000 pounds be phased out by January 1, 2000, and be replaced with Stage 3 designs. Currently, the international aviation industry is moving towards Stage 4 designs which will reduce noise a little further, although most presently manufactored commercial aircraft already meet the new standards. Top of Page

Population affected by the airports. National Airport operations impacts over 800,000 people (using 1990 census data). These are the people who live in the areas adjacent to the airport or the Potomac River Corridor. Are all of these people affected equally? The answer is no for several reasons. First, of the 800,000 people, those living closest to the River and nearest the airport will hear more noise. People living several miles away will hear less noise. Second, not everyone is annoyed by aircraft noise. The official Government figure is that 12 to 15 percent of a local population are highly annoyed by aircraft noise. A new look at the original research, however, says that at 65 DNL, the number of highly annoyed people is more like 27 percent. Another recent study quotes figures as high as 70 percent.

When Dulles International Airport is included, the total number of people impacted rises to 935,000. Dulles is located in a more rural area, although from 2000 to the present, that has rapidly increased in population due to the development of new communities around Dulles.

Factors that affect the level of noise. Other factors affect the amount of aircraft noise one will hear. Wind direction can increase the noise if the prevailing wind blows from the aircraft towards the recipient. Aircraft orientation can increase the noise or decrease the noise depending on which way the rear of the aircraft is pointing. Humidity also affects the amount of noise one perceives. The time of year increases or decreases the level of noise. Here in the Washington area, in the late Spring through to the middle of the Fall, the noise is somewhat attenuated because the folliage absorbs some of the noise. When the leaves drop off the trees, the noise will be perceptively higher. Top of Page

Noise abatement procedures - Noise abatement procedures can help reduce the impact of jet aircraft noise on citizens living near the airport or along the flight paths. For National Airport, flights are directed to follow the Potomac River, Anacostia Rivers or over the south Arlington area. Planes using Runway 1 fly to the 10 mile DME (Distance Measuring Equipment - indicates the distance to/from the airport) to the northwest or if using Runway 19, to the 5 mile DME to the south. For aircraft using Runway 3, they would fly up the Anacostia River to the 5 mile DME. Alternately, instead of flying northwest up the river when the weather is bad, northbound departures may follow the compass heading of 328 degrees once reaching the Georgetown Reservoir. Under IFR (Instrument Flight Rules) conditions, radar vectors are used together with VOR (VHF omni-directional range) guidance. Propeller-driven aircraft are directed to follow the river where possible until reaching altitudes of 1500 feet for single or twin-engine aircraft and 2000 feet for four engine aircraft. For landings, aircraft will also follow the river corridors.

The noise abatement procedures for jet aircraft incorporate a power reduction at 1500 feet altitude when reaching the 2 mile DME point to the north, or the 3 mile DME point to the south. The specified thrust cutback at that point is calculated using aircraft performance to maintain the requested 500 feet per minute climb-out at maximum weight on a hot day. This reduced rate of climb is maintained until the aircraft reaches the 10 mile DME point (north direction) before any additional power is added. Propeller aircraift have no climb profile restrictions.

It should be remembered that the noise abatement procedures are not mandatory, but are in the official category of "advisory"; which means that the pilots and air controllers can ignore them at their convenience. If they are ignored too often, the Metropolitan Washington Airports Authority (MWAA) should file a complaint with the offending airline or with the FAA. Top of Page

Nighttime operations
There is no nighttime curfew at National Airport. There is a nighttime noise limits for arrivals and departures, and they remained in effect from 10 p.m. to 6:59 a.m. The aircraft noise limits are 72 dBA for takeoffs and 85 dBA for approaches.

Dulles Airport, because of its 10,000 acre size which is large enough to provide a buffer for the surrounding communities, does not have any noise abatement procedures. The airport operates 24 hours a day using any type aircraft.

Noise measurements
Noise is measured using a logarithmic scale. Examples are: if the noise power doubles, that would be a 3 decibel (expressed as dB) change; if the power goes up by a factor of four times, that would be a 6 dB increase; for an increase of 10 times, the decibel change would be 10 dB, and for 100 times, 20 dB. One can see that logarithmic scale compresses the measurements and makes them appear to be less than they actually are. When you hear someone say that it is only a 3 dB increase in noise, it means they have doubled the noise power and you will probably noticed it, particularly at night when the ambient noise is quieter. During the day, especially in an urban setting, it may be harder to distinquish a 3 dB increase.

What are some benchmarks for sound level?

- Normal conversation - 45 to 50 dBA (The "A" mean that the sound measurement follows the human ear frequency response curve, roughly 60 to 3000 hertz)
- A food blender at 3 feet - 90 dBA
- A vacuum cleaner at 10 feet - 70 dBA.

These sounds levels are the peak noise level. For aircraft, the term used is SEL (single event level). Different types of aircraft produce different levels of peak noise. The Concorde produces a SEL of 112 dBA while regional jet aircraft produce only about 67 dBA. A difference of 45 dB is an enormous number, specifically a factor of 31,623 times. Making sense of a day's worth of noise data is not easy if one is trying to create an easy-to-use metric. To simplify the noise measuring task, Government scientists created the Leq (equivalent noise level). The Leq basically takes each noise event and devolves it into a one second event with an appropriate amplitude. They then sum all these one second events for the day (24 hours) creating an average for the day. However, the Government recognized that nighttime air traffic would disturb people's sleep so they applied a 10 dB "penalty" to the Leq for the nighttime hours from 10 p.m. to 7 a.m. This number, which is also an average, they called the Day Night Level or DNL (sometimes you will see it written in its older form, LDN). Top of Page

The 65 DNL noise threshold
In 1978, the Federal Government via the FAA established a noise threshold which it thought residents should be expected to tolerate. This threshold level was set at 65 DNL which is, of course, a 24 hour average. It was agreed that if the DNL exceeded 65 dB, the airport operator or local government could implement mitigation procedures such as buying out residents living within the 65 DNL contour (analogous to elevation contours on a map), or sound proof the owner’s home. The 65 DNL number was selected primarily on technological and economic grounds, not on what was good for the residents' health. The Environmental Protection Agency (EPA) argued that for people's health and peace of mind, the threshold should be no higher than 55 DNL. The EPA lost that argument for the following reasons. In 1978, aircraft technology was such that an airport's fleet of aircraft could not achieve any better performance than 65 DNL (over 24 hours). Also, the Government knew that if they used a lower threshold, especially the 55 DNL the EPA wanted, it would have to spend hundreds of billions of dollars to either buy up homes or provide noise insulation for homes, schools, and hospitals. Since that time, the 65 DNL number has been used as the benchmark for receiving Federal funds, although the FAA has softened its stand recently and will consider lowering the threshold to 60 dB in special cases. After the 1978 decision, the American National Standards Institute (ANSI) codified the threshold levels for human activities. The standard covering noise threshold levels is ANSI S3.23. It should be noted that the standard specifies that thresholds above 65 DNL is incompatible with residential living. The Washington area has three communities which are living with noise above 65 DNL on a yearly basis, but as yet have received no mitigation funding because they have not thought to ask for it.

Noise monitoring
Many large airport operators place noise monitoring equipment within the community to assess the changes in average noise levels. This gives the citizens a crude measurement of the noise impact they are living with. The Metropolitan Washington Airports Authority has such a system. It has 32 -- soon to be increased to 40 -- noise monitoring stations up and down the Potomac River, within Washington D.C. and around Dulles Airport. There are 20 stations monitoring National Airport traffic, and 12 -- being increased to 20 in early 2009 -- monitoring Dulles traffic. Each station is basically a microphone mounted on a pole and a processor. The microphone collects all sounds, community as well as aircraft. It cannot distinguish between community noise and aircraft noise. The data is collected for 24 hours and transmitted by telephone lines to the Airports Authority which then runs the data through another processor. This processor tries to identify from the noise data if there are any aircraft present by "listening" to noise above an empirically selected threshold (typically 70 dBA). If a sound exceeds this threshold for 10 seconds, it is likely to be an aircraft, and is then compared to actual radar data, obtained a few days later from the FAA, to confrim that it is an aircraft. If, however, the aircraft sound falls below the threshold for an instance during the 10 seconds, the sound is assumed to have been made by community activity. Unfortunately, this system ignores the potential for reflected noise sounds which can cancel the actual aircraft sound when it reaches the microphone thus creating a "hole" during the 10 second measuring time. The "hole" negates that aircraft event. CAAN believes that the system's lack of sophisication may be unduly penalizing communities; that is, it is reporting community noise levels higher than they actually are, and conversely, reporting a lower level of aircraft noise than it should be. This fact has been presented to the FAA and our Airports Authority by CAAN and others, but no official action has been taken. Top of Page

Noise Measurements for the Washington D.C. Area

CAAN has been analyzing the Airports Authority's (MWAA) published data for the last 10 years and recompiled this data in a form that can be more readily understood by the each affected communtiy. The data shown in Table1 below give the noise data for the previous three years for aircraft noise expressed in DNL (Day Night Level) for each noise monitoring station. Readers should realize the three year average is itself an average; that is, MWAA publishes the average for each month (itself an average of each day in the month) and then that average is averaged once again. This means that the DNL numbers you see in the table are thrice removed from the reality of what you actually heard on any past date. Therefore these readings are only an indicator of the true situation. Nevertheless, they are the numbers which MWAA and the FAA use to determine if a community will be considered for noise mitigation. To be considered for noise mitigation, the DNL average for the year from aircraft noise alone (not from community or community plus aircraft noise) must be 65 DNL. As the table below shows, over three years, there are three communities which meet that criteria, four if only the last years' data is used. These communities can request noise mitigation from MWAA and should do so if the majority of the residents object to aircraft noise.

The table also shows the aircraft noise level for the last year alone (a year for this data runs from October through Septmenber). Based on this one year criteria, Chain Bridge has moved from below 65 DNL to above 65 DNL. In other communities, some have had higher noise levels this past year while in others the noise level decreased.

The fifth and sixth columns of the table show how the noise levels have flucuated over the past two years. Readers will notice that in some communities the noise went up during the '98 - '99 year and down in the '99 -'00 year. Others went up or down both years. Several communities had dramatic changes in the past year. Cabin John in Maryland had over 6 dB drop while Dumbarton and Aldie in Virginia had 8 dB increases. Last year the Mt. Vernon citizens raised a loud cry of protest about the aircraft noise levels in their area. When the politicians and other community leaders picked up their cause, the FAA responded with "adjustments" to the flight paths. Their noise level then dropped by 11 dB. Strong citizen action can make a difference.

Finally the table shows that, contrary to FAA pronouncements that aircraft noise is decreasing, noise is actually increasing for some Washington area communities, and in some cases substantially (e.g. 8 dB). With Dulles Airport increasing the number of flights significantly, residents around Dulles can expect more noise, even though the aircraft are supposedly getting quieter. To make it worse for citizens around Dulles, two new runways will be added, one by 2006 and a second a few years later.

The table reveals that 14 communities had increases in noise this past year, 15 had decreases, and three were basically unchanged (defined as less than one quarter dB change). The year before, the noise went up in 14 communities, down in the other 11 with 7 unchanged; but the mix was different.

In the table below, the names in blue are for National Airport noise monitoring stations. Those in magenta are for the Dulles Airport noise monitoring stations. The DNL values in red are stations where the aircraft noise is 65 or greater, and those in yellow are stations where the DNL values lie between 60 and 65 dB. Top of Page

AUGUST 2005: CAAN HAS LOOKED AT THE MOST RECENT YEARLY NOISE LEVELS AVAILABLE AND COMPARED THEM TO THE 2000 FIGURES, THE YEAR PRECEDING THE 2001 TERRORISTS ATTACKS. THE NOISE LEVEL FOR SOME COMMUNITIES HAS INCREASED AS MUCH AS 4.3 dB (2.7 TIMES THE NOISE). HOWEVER, OTHER NOISE STATIONS HAVE DECREASED BY AS MUCH AS 9.4 dB (A NOISE REDUCTION OF OVER EIGHT TIMES). TABLE 2 MAKES THE NOISE STATION COMPARISONS. SOME OF THESE REDUCTIONS MAY BE ATTRIBUTED TO FEWER FLIGHTS DUE TO THE 9/11 ATTACKS AND PEOPLE'S RELUCTANCE TO FLY, SOME TO THE FINANCIAL PROBLEMS THE AIRLINES ARE HAVING AND STILL OTHERS TO CHANGES IN RUNWAY USAGE.

Washington area communities which would like to learn more about their noise situation should contact CAAN via our email.

Table 3 shows the average noise levels for the year April 2005 through March 2006. It also shows that there is only one noise station with DNL noise levels greater than 65 dB and that is again Arcola, VA which is west of Dulles runway 12/30. However, the Bolling AFB noise station has been inoperative for the whole year, and it usually usually exceeds the 65 dB level. So the noise levels from Arcola and Bolling AFB remain the two prime offenders. For stations with noise levels between 60 dB and 65 dB, one can see that there is now only one, quite an improvement from the year 2000 levels. Progress has being made in reducing the noise levels for many communities over the last year, some rather dramatic, like Avenel (—11.2 dB), Dumbarton (—8.5 dB), and Chevy Chase (—7.5 dB). However, before we cheer, there were some communities which had increases in noise level, like Broad Run Farms (+6.9 dB, almost five times its previous noise level) and Springfield (+4.3 dB, about 2.7 times the noise). It should be noted that no data from the noise monitoring stations has been available because the entire system has been off-line. A new system is currently (Fall 2008) being installed and should be ready for use by early 2009. Top of Page

Noise mitigation funding
There are two sources of money to implement noise mitigation, Airport Improvement Program (A.I.P.) funds and Passenger Facility Charge (PFC) funds. The A.I.P. funds come from Congress via its appropriation/ authorization process. However only a small portion of the Transportation budget is allocated for noise mitigation, less than 10 percent. To obtain A.I.P. money, the airport operator - MWAA in our case - must submit a plan to the FAA for the specific mitigation action it wishes to take. After a long approval process, the project is put on a waiting list with many other fund requests. Eventually, the project may merit funding if other projects do not take precedence. Currently, there is a long waiting list to obtain this type of money.

PFC funds are derived from the passenger ticket fee which presently is $4.50 per ticket. The money is collected by the airlines at each airport and given to the airport operator. The airport operator - for us MWAA - can then use it to expand facilities or use it for noise mitigation. In either case, MWAA must get FAA approval to spend the money; however, approval is usually pro forma provided the PFC money conforms to required broad categories. In the past 22 years, MWAA has never applied for A.I.P. or used PFC funds for noise mitigation.

Communities which are living at 65 DNL or greater due to aircraft noise alone have to request mitigation funds from the Airports Authority; The Authority will not initiate action unless it hears from the individual community. Top of Page

Air emissions/water pollution and its control
Jet aircraft discharge large amounts of pollutants and although jet engines have improved over the years, they are still responsible for considerable air pollution. For instance, a single 747 takeoff is equivalent to running two million gas-powered lawnmowers at once. Current Federal laws exempt commercial aircraft from the clean air laws, so little has been done in the way of monitoring air quality around airports. As a consequence, as air taffic increases, the EPA has no choice but to clamp down harder on the other regional industries to keep air quality goals on target.

Now researchers have reported that there appears to be a health threat from these emissions. Within the past few year, studies have been published that show that people living within three miles of an airport or its flight paths have higher disease rates - 20 to 40 percent higher - for such diseases as heart, cancer, asthma and other respiratory ailments, and pregancy complications.

Water pollution from airport activities are from many different toxic chemicals. Although airports must conform to the clean water laws, the EPA often grants exemptions, and pollutants are allowed to run into nearby waterways. At National Airport, deicer and anti-icing chemicals, at the rate of 100,000 gallons per year, are allowed to run into the Potomac River. MWAA is currently looking at ways to contain this outflow, but there is little real estate to build a collection facility. At Dulles International Airport, there is a holding pond for the collection of chemical runoff; however, any overflow from this pond will feed into the Potomac River via smaller tributaries. Monitoring of chemical outflows from these airports has been lax at best, and even when measurements were taken by the EPA, and chemicals were found to be far above the Federal limits, nothing was done about it.

Helicopter activity
Helicopters have been an increasing source of noise in the Washington area. The military, which accounts for 90 percent of the helicopter traffic, have increased their activity by 40 percent since 1997. Although there are designated routes for helicopters, not all pilots use them. Also, prohibited areas like Arlington National Cemetery are often ignored by the FAA and helicopter pilots, even though all parties agreed to the prohibition in 1992. Tracking the military helicopters flights is not possible because their flight data is classified and is not sent to MWAA for analysis. Although there is a helicopter association who works with local goverment agencies, there is no current mechanism to limit helicopter activity. Helicopters are suppose to fly at 1000 feet above the ground (except for emergency helicopter operations, and flying up the Potomac River from National Airport), but often do not obey this rule. Top of Page

FAA operations
The FAA divides air traffic control into three functional areas, airport tower operations, TRACON operations, and enroute operations. Each has a specific area of responsibility.

• Airport Tower Operations. The Tower operators are responsible for the orderly flow of air traffic into and out of the airport. They are also responsible for aircraft movements around the airport. Their responsibility zone is anything within five miles of the airport.

• TRACON Operations. Terminal Radar Control (TRACON) picks up responsibilty for the departing aircraft from the tower operator and directs it into the Enroute System. The TRACON air controllers maintain separation of all aircraft within 50 miles of the airport. It is their job to sequence arriving aircraft to the designated runway.

• Enroute Operations. The enroute system is responsible for air traffic flying between regions of the country and normally operates from about 17,000 feet to a typical ceiling altitude of 37,000 feet, although the Concorde flies higher than that. There are 21 enroute centers across the country and as the aircraft flies from one area of the country to another, it is handed from one center to the next until the aircraft reaches the TRACON where its arrival airport is located.

FAA responses to queries.
Many of our supporters are frustrated by the FAA response to the question: "Have you changed the flight patterns so that I am seeing more planes over my neighborhood?" Their answer is often, "No, we have not changed any procedures." And their answer is correct as far as it goes. They have not change their procedures which are the way they handle aircraft, but they do have wide latitude in where they tell the aircraft to fly, and that, many times, is what they have done, moved the planes over to a new route for some period of time. Their reasons for this could be, for instance, to improve airport capacity, adjust to seasonal weather patterns, or military activities (not too often). If there is a crush of airline flights trying to take off within a short time period like the day before Thanksgiving, air controllers may send the planes out of the noise abatement pattern earlier than the 10 mile DME (or 5 mile DME to the south), thus flying them over communities which normally do not experience air traffic. Readers should remember that the FAA is constantly trying to improve what they call the "safe, expeditious and orderly flow of traffic", which will improve or minimize the air time for the airlines. Their radar screens do not show what is on the ground and except for restricted air space, meaning prohibited airspace like the White House, and their TRACON boundary lines; they are not especially concerned about the noise in residential communities.

Metropolitan Washington Council of Governments/CONANDA
The Washington area has a regional authority (usually referred to as "COG" (Council of Governments) which corrdinates intergovernmental activity between the District, suburban Maryland and suburban Virginia. COG has a committee called the Aviation Policy Committee (APC) (the old name was Committee on Noise Abatement and Aviation at National and Dulles Airports (CONAANDA)). This body works to reduce the impact of noise around the two airports. People living in the Washington area may call the APC office at 202/962-3355 to learn of their activities. Top of Page