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Aircraft Noise: Plane Sense on Engines
The issues for older aircraft- and the available solutions.

The issue of aircraft noise and the complaints that generate from it are continually falling upon the desks of most airport managers pretty much everywhere- regardless of the airports’ size or the number of operations at that airport. It is a common joke among airport managers that it takes several months after completing a househunting search- transaction closing and move-in before new local residents discover that there is an airport within their neighbourhood - and once they do finally discover it- they usually start telephoning to complain of noise.

Unfortunately- it is easy for industry insiders to make light of the noise- and in doing so we disenfranchise ourselves from reality. The following paragraphs will attempt to help all of us open our eyes- and minds to this hot and often political issue. First- some mechanical detail:

The noise that is generated by a turbine aircraft emanates from four specific areas- including:
• Engine Fan and Compressor Sections (engine noise – most on take-off);
• Engine Combustion and Turbine Sections (engine noise – most on take-off);
• Engine Exhaust (engine noise – most on take-off);
• Various Airframe components like the under carriage- flaps- airbrakes- and wing trailing edges (aerodynamic noise – most on approach and landing).

Both temperature and humidity has an effect on perceived noise. The colder and the more damp that conditions become- the louder and/or further away the noise is perceived by people on the ground. Rain and snow do however have a sound muffling effect.

In the U.S. the issue of aircraft noise has been researched- panelled- discussed- analyzed- studied and measured for decades. In 1993 the Federal Interagency Committee of Aviation Noise (FICAN) was created by bringing together representatives from the U.S. Air Force- U.S. Army- U.S. Navy- National Park Service- Federal Aviation Administration (FAA)- U.S. Environmental Protection Agency (EPA)- National Aeronautics and Space Administration (NASA)- and the Department of Housing and Urban Development.

One of FICAN’s highest mandates was to Research into community reactions to aircraft noise- including sleep disturbance- non-auditory health effects and speech interference- as well as the development of improved assessment criteria for these effects. Before FICAN came into existence the majority of aircraft noise research took place in the 1960s and 1970s.

Aircraft noise became a legislative issue as the airline and Business Aviation industries began converting their aircraft fleets from propeller to turbojets- and air-travel became more popular. In 1968 the FAA was forced by a bill passed by the U.S. Congress to amend the Federal Aviation Act whereby noise standards had to be considered before a Type Certificate was issued to an aircraft manufacturer. This bill created Federal Aviation Regulations- Chapter 36: Noise Standards: Aircraft Type and Airworthiness Certification to be created and signed into law in 1969. Later in 1972 the Noise Pollution and Abatement Act was passed into law- and then the Quiet Communities Act was added in 1978.

The FAA requirements in Chapter 36 in 1969 specified that no aircraft during either take-off or landing could exceed a noise level of 112 EPNdB (Effective Perceived Noise in Decibels) while the target maximum standard was set at 108 EPNdB. The maximum allowable noise level was lowered in 1988 down to 110 EPNdB. Today it is set at 108 EPNdB.

To place all of this into context- the quietest sound that a human ear is capable of hearing is 16 dB. In general- perceived ‘Loudness’ doubles with every 10 dBs added. Human conversation between two people sitting facing each other will usually register at 50 dB’s on a noise monitor. 110 dBs is equivalent to 64 times the volume or loudness of that conversational human speech.

Without noise suppression- a normal person will feel pain once noise reaches 140 dBs.

During the introduction of Chapter 36 of the Federal Aviation Regulations- the FAA created a noise classification table for turbojet powered aircraft that is divided up into three stages. Noise levels for ‘Stage’ defined aircraft are measured at three points. These points are designed to measure noise levels for take-off; approach to landing; and fly-over- defined as sideline noise. Additionally the number of engines on an aircraft also affects its stage classification.

A Stage 1 noise level means a take-off- flyover- or approach noise level greater than the Stage 2 noise limits.
Stage 2 noise limits for airplanes regardless of the number of engines are as follows:
• For Take-off: 108 EPNdB for maximum weights of 600-000 pounds or more- reduced by 5 EPNdB per halving of the 600-000 pounds maximum weight down to 93 EPNdB for maximum weights of 75-000 pounds and less.
• For Sideline and Approach: 108 EPNdB for maximum weights of 600-000 pounds or more- reduced by 2 EPNdB per halving of the 600-000 pounds maximum weight down to 102 EPNdB for maximum weights of 75-000 pounds or less.

Stage 3 noise limits are as follows:
• For Take-off: airplanes with more than three engines- 106 EPNdB for maximum weights of 850-000 pounds or more- reduced by 4 EPNdB per halving of the 850-000 pounds maximum weight down to 89 EPNdB for maximum weights of 44-673 pounds or less.
• For Take-off: airplanes with three engines- 104 EPNdB for maximum weights of 850-000 pounds or more- reduced by 4 EPNdB per halving of the 850-000 pounds maximum weight down to 89 EPNdB for maximum weights of 63-177 pounds or less.
• For Take-off: airplanes with fewer than three engines- 101 EPNdB for maximum weights of 850-000 pounds or more- reduced by 4 EPNdB per halving of the 850-000 pounds maximum weight down to 89 EPNdB for maximum weights of 106-250 pounds or less.
• For Sideline: regardless of the number of engines- 103 EPNdB for maximum weights of 882-000 pounds or more- reduced by 2.56 EPNdB per halving of the 882-000 pounds maximum weight down to 94 EPNdB for maximum weights of 77-200 pounds or less.
• For Approach: regardless of the number of engines- 105 EPNdB for maximum weights of 617-300 pounds or more- reduced by 2.33 EPNdB per halving of the 617-300 pounds maximum weight down to 98 EPNdB for maximum weights of 77-200 pounds or less. The Stage 4 noise regulations are applicable to all new type designs introduced after January 1- 2006.

This latest ‘stage’ standard is related to the Stage 3 requirements and is summarized as follows:
• A cumulative margin of 10 dB relative to Chapter 3
• A minimum sum of 2 dB at any two conditions
• No trades allowed.

The Appendix section of the current FAA Advisory Circular 36-1H lists all U.S. Type Certificated and foreign certificated aircraft and helicopters along with their respective certified Stage Noise Levels.

The quietest business aircraft is currently the Cessna Citation 560 Encore which is equipped with two Pratt & Whitney PW535A engines. Its take-off noise level is only 70.3 EPNdB- which is about half of the sound-level of that made by a telephone dial-tone- and is therefore well under the current Stage 4 requirements.

Airports that are located in noise sensitive areas (a densely populated area or a nature reserve- for example)- will often introduce and require aircraft operators to adhere to noise abatement policies and procedures- curfews- aircraft bans- slot limitations- capacity limits- preferential runways- displaced landing thresholds and take-off points- as well as possible restricted engine ground running areas- all as viable countermeasures to reduce the number of noise complaints that airport management receives.

In 1991 the FAA introduced a new section to its regulations titled Part 161: Notice and Approval of Airport Noise and Access Restrictions. This new part was in compliance of the Airport Noise and Capacity Act which was passed into law in 1990. Until the framing of this act- airport noise restrictions had been created and imposed by local municipal and state authorities that had been pressured by public opinion to do so.

What this act and Part 161 did to help airport managers fighting noise complaints all across the U.S.- was to provide defined structural procedures that had to be followed before any noise restrictions were implemented by airport management at a federally approved airport. Part 161 was given teeth by making the provision that any airport that does impose noise restrictions without meeting the requirements specified by this Part- will give the FAA sufficient grounds to rescind all federal funding to that airport.

The bottom-line of this discussion- is that if you have a Stage 2 aircraft- you are probably living on borrowed time. Already Stage 2 aircraft that have a Maximum (Ramp) Weight greater than 75-000 lbs have been grounded since January 1st- 2000. The venerable Gulfstream models that currently fail to meet Stage 3 noise requirements- can reach 70-000 lbs maximum weight- and are therefore likely at the greatest risk of grounding if the current weight limit is reduced.

Fortunately for most current Stage 2 aircraft there are either Engine Retrofit or Hush-Kit modifications available to make Stage 2 aircraft Stage 3 compliant. The table (below) lists how Stage 3 is achieved on some of the Stage 2 aircraft.

Unfortunately in the case of Stage 3 compliance achieved by undergoing an engine retrofit program- aircraft values have fallen well below the modification costs - so-much-so that many conversions are just not economically viable. I will use the Dassault Falcon 20 series as an example to illustrate. Even though it is probable that there are two or three retrofit kits still in existence- to allow the conversion of several more Falcon 20s- the likelihood of this happening is highly improbable.

Since the Honeywell TFE-731 engine retrofit program started in the late 1980s- there have been 117 aircraft that have undergone the conversion- and now sport Honeywell- instead of their old General Electric CF700 engines. Today 30% of the fleet are available for purchase in a used condition.

Conversions at the peak of this program normally cost around $4-500-000 to have accomplished. This was on top of the initial acquisition price of the candidate aircraft itself. Many Falcon 20F models (for example) trickled onto the used market in the $7-9m range- post engine conversion. Most sold quickly- because there was high demand for these large-mid cabin aircraft that gained almost a doubling of range due to the improved fuel efficiency of the retrofitted engines.

23 Falcon 20 basic models (13% of the 173 model fleet)- six Falcon 20D models (10% of the 61 model fleet)- 13 Falcon 20E models (21% of the 63 model fleet) and 75 Falcon 20F models (54% of the 138 model fleet) have all since been converted. Notwithstanding avionics differences between each model- in the 1990 a Falcon 20C- 5BR (basic model) would trade $2-000-000 (average) less than a Falcon 20F-5BR. Now in today’s market virtually none of the models will break $2-000-000 during a sale- while many- including F Models- sell at or below $1-000-000.

Why has the Falcon 20-5 Market been levelled so quickly- you might ask? It all boils down to age. Production deliveries of the Dassault Falcon 20 started in 1965 and pretty much ended in 1985. The oldest Dash-Five Falcon has celebrated its 44th birthday this year. There is both a force of natural attrition- and also an-industry attrition which determines the useful life of a product like a business aircraft.

Natural attrition is determined by the cost of replacement parts availability and cost. Industry attrition is determined by the banks that lend money to purchasers of these products. Both systems normally run fairly close together- but in the last 50% or so of a product’s life- industry begins to lead the natural state by 15 to 20 years.

In the early 1990s- most banks were quite vocal in letting buyers know that they were reluctant to finance aircraft that were manufactured before 1980. By 2000 that year-model comfort threshold had risen to 1985. By 2005- 1990 was the norm- and now today- in early 2011- while we are all still recovering from the worst recession in living history- that threshold has leapt-up to the smallest gap ever - 2005.

Banks just don’t like old aircraft. Of course you can borrow money to snatch up an incredibly deflated value Dassault Falcon 20F-5BR (80%+ discount from ten-years ago)- but there is a strong likelihood that you will have to put 80% of the money down as your collateral down-payment- while you are allowed to borrow only 20% of its purchase price. This would have been in reverse 36 months ago (20% down and 80% financed).

The same economics apply to the other Stage 2 aircraft that I listed in Table A- however there is probable chance that the Hush-Kit programs for the Gulfstream GII/IIB and GIII series aircraft will continue to live on- with returns provided to the companies that have invested millions of dollars to develop and have approved an FAA Supplemental Type Certificate for the installation of their Hush-Kit designs.

I say this because even though these aircraft burn about 10% more fuel than their younger Stage 3 compliant sister aircraft - the Gulfstream GIV/IVSP - the cabin size and range of these aircraft deliver figures that are near-impossible to equal without an initial cash outlay of $10 million- plus for an equivalent.

The current values of the old Stage 2 Gulfstream aircraft are plumbing the same depths- and in some cases lower- as those of the Dassault Falcon 20 Retrofit series. This fact makes the installation of a Jet-pipe Exhaust after-body Hush-kit still economically viable. Please allow me to demonstrate and conclude with a comparison between the GIII and the GIV via the tables below.

Jeremy Cox draws on a wealth of experience as a pilot- an aircraft engineer/ mechanic and an aviation writer. He currently serves as Vice President at JetBrokers- Inc - a professional aircraft sales company. More information from jcox@jetbrokers.com

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