The approach of stricter noise-control legislation means good business for engine hushkitters.

Andrew Doyle/LONDON

THE CONCEPT OF hushkitting has been around for almost as long as the civil jet-engine itself. Recent legislation, however, has forced airlines to reconsider this relatively primitive approach to reducing the noise emitted by their aircraft as an alternative to the much more costly options of re-engineing them or acquiring brand-new airliners.

Many airlines really have no choice other than to hushkit - either they cannot afford to re-engine or buy new aircraft, or there is no re-engineing option available for many of their types, or there are no obvious replacement aircraft. Other carriers, such as Northwest Airlines, have taken the hushkitting route because they consider it to be the most cost-effective option in the long term.

Some hushkit manufacturers have targeted specific types - such as Nordam with the Boeing 737-200 - where there are large numbers of relatively young aircraft still in operation. Other hushkit makers have concentrated on what are generally much older aircraft - Quiet Nacelle (QNC) and Burbank Aeronautical, for example, are focusing on the Boeing 707 and McDonnell Douglas (MDC) DC-8. The predominantly cash-strapped operators of these aircraft have not been offered a re-engineing option for many derivatives and cannot see an obvious replacement for these types, or are unable to afford new aircraft.

The AvAero (737), ABS (MDC DC-9) and Burbank Aeronautical (707/DC-8) programmes are all backed by Pratt & Whitney, which is anxious to see the huge installed base of JT8Ds and, to a lesser extent, JT3Ds, continue in operation, as it does not have an equivalent powerplant to offer for new-build aircraft. For example, it is likely that, if 737-200s were withdrawn from service in large numbers, many would be replaced by new-generation 737s or Airbus A320s - the former powered exclusively by CFM International CFM56s - denying P&W significant revenue from spare-part sales.

"We got into these hushkit programmes because we were concerned about keeping the JT8D flying," admits David Sheppard, P&W JT8D programme manager. "Our philosophy when we started in 1988 was to ensure that there was at least one hushkit programme for each JT8D-powered aircraft. We want to keep as big an installed engine base as we can."

Apart from the capital cost of hushkitting, several other factors make the equation more complex. Many operators of non-Stage 3 machines have sold their aircraft and leased them back, opening up the question of whether the operator or the lessor should fund the modification. In addition, there is likely to be a last-minute rush as those operators which have delayed hushkitting for as long as possible try to meet the Stage 3 deadlines (see box, P26).

Also to be considered is the inevitable thrust loss, extra weight, or increased fuel consumption associated with hushkitting. Airlines in Europe face the additional problem of significantly inflated landing fees for non-Stage 3 aircraft.


There is speculation that tougher, so-called "Stage 4", noise regulations may be on the horizon, with the Committee on Aviation Environmental Protection, a branch of the International Civil Aviation Organisation, due to meet in December to discuss the latest proposals. Regulations governing exhaust emissions may also be introduced.

QNC, in common with most other hushkit manufacturers, plays down the impact of its hushkits on the performance of modified aircraft. The company is focusing on the market for the 707 and the US Air Force's "open-skies" derivative of it, the OC-135B, and is developing a Stage 3 hushkit concurrently for the P&W JT3D and TF33, which power the two types, respectively. Ground acoustic and performance testing was completed earlier this year, and production of the first shipset of components has now begun.

According to Martin Gardner, QNC's OC-135B project manager, the thrust loss and increased fuel consumption associated with the hushkit will be "marginal". In fact, adds chief engineer Terry Marshall, as far as the OC-135B and 707-100 are concerned, there will be no thrust loss at all and the hushkitted aircraft will consume less fuel than they did when fitted with QNC Stage 2 hushkits. Gardner also maintains that there will be no payload restrictions, as the 707-300 will meet Stage 3 requirements even at maximum gross weight.

This performance has been achieved using "applied, proven, technology", says Marshall. "The biggest benefit is lighter-weight materials - acoustic technology hasn't changed," he adds. The kit includes an inner acoustic ring at the engine intake, and is constructed from acoustically treated carbon-reinforced-plastic honeycomb.

The potential market for hushkitting 707s is substantial - QNC claims that there are 154 (almost exclusively cargo) 707s on the civil register worldwide, plus a further 40-45 aircraft in the VIP/corporate role. Of these, the company is expecting 100-150 aircraft to require hushkitting, with the break-even point, according to Gardner, being for only 20 aircraft shipsets. The USAF could require up to 200 C/KC-135Bs to be hushkitted, he adds.

The USAF has re-engined a large number of KC-135s with the CFM56 turbofan, but Gardner believes that re-engineing commercial 707s will never be a viable proposition. "It's purely expense," he says. "The cost of re-engineing [with the CFM56] is over $30 million per aircraft - only the US Government has got that kind of money."

He also argues that, for airlines operating 707 freighters, "...there is no kind of equivalent aeroplane". The cost of hushkitting a 707 with QNC equipment, says Gardner, is only $2.75 million, including installation.

QNC's first 707/OC-135B hushkit should be installed on the number two engine of a USAF-owned WC-135B test aircraft by the end of November, with first deliveries of hushed OC-135Bs scheduled to take place early in 1996. According to QNC, this should be closely followed by an application for a supplemental type certificate for the commercial 707-100 series, which is almost identical to the OC-135B airframe, with deliveries to airlines commencing soon after. The 707-300-series hushkit should be certificated later in 1996.

The company has also been selling hushkits for the DC-8-50 and -61 for several years, having been established in 1984 to develop a Stage 2 hushkit for the DC-8. Flight-testing of a Stage 3 hushkit for the DC-8-50/61 is under way, and the first flight of an aircraft with a production kit fitted to the number two engine should take place in November, says QNC.

Much of the potential market for hushkitting DC-8-61s (and -63s) was pre-empted in the early 1980s, with a substantial number of aircraft being re-engined with CFM56s, although Marshall sees around 90 candidate -50s and -61s. "We're really only targeting around 50 aircraft," he says, with orders so far from two US operators. The cost of the upgrade, including installation, would probably be higher than for the 707 because there is a smaller overall market for this aircraft, he adds.

Burbank Aeronautical II (BAC II) also believes that many 707 and DC-8 operators will opt to buy hushkits, and the company has decided to join QNC in this market by offering a modification for the 707-300 and the DC-8-50/-61.

According to Ken McGuire, president of BAC II, a market for around 100 Boeing 707-300 Stage 3 modifications and 70 DC-8-50/61 shipsets exists, as well as for potential military sales. The kits will add, about 900kg and cost around $3.25 million, an aircraft.

BAC II expects to complete "baseline" 707 flight-testing this year, achieving certification of the engine test-cell in the first quarter of 1996, followed by flight-testing of a modified 707 in the second quarter. US Federal Aviation Administration certification and initial production is planned for mid-1996.

BAC II certificated a Stage 3 kit for the DC-8-62/-63 in 1990, but claims that it will be "a far more difficult effort" to design a hushkit which will allow the 707 or the DC-8-50 and -61 to comply with Stage 3 requirements.


This is because the DC-8-62/-63 has a larger wing span and more aerodynamically efficient engine pylons than those of the -50/61, and longer fan-exhaust ducts than either the -50/-61 or the Boeing 707, which allows lower thrust settings to be used for approach or take-off at a given weight, and gives a greater fan-duct area for acoustic treatment. "In addition, the DC-8-62/-63 fan-exhaust air exits just upstream of the turbine exit, which substantially reduces sideline noise," adds BAC II.

"This is not true of either the DC-50/-61 or 707, and results in starting sideline noise levels several decibels higher than those of the DC-8-62/63," says BAC II.

Following an agreement earlier this year, P&W will develop and manufacture a re-spaced inlet guide-vane for the JT3D, and assist BAC II in the development of an internal exhaust-gas mixer for these engines.

P&W claims that, because of revised aerodynamics around the engine and nacelle and improved thermodynamic performance, there will be "no degradation in fuel burn, and a possible improvement of up to 2% in the BAC II Stage 3 hushkits for the DC-8-50/-61 and 707". A retrofit programme is planned, to incorporate these improvements in BAC II Stage 3 kits for the DC-8-62/-63.

An affiliated company, Burbank Nacelle, is part of the ABS partnership, which is the sole producer of hushkits for the DC-9. Burbank Nacelle also manufactures acoustic inlets for the FedEx Stage 3 727 hushkit and the ABS DC-9 programme.

The third project on which QNC is working involves hushkitting the British Aerospace One-Eleven, powered by Rolls-Royce Spey engines, following the signing of a memorandum of understanding with European Aviation earlier this year.

Marshall admits that the type will suffer a more significant thrust loss and increase in fuel consumption than the 707 or DC-8, because of the "...extensive noise reduction that has got to be accomplished". He adds: "There will be a thrust loss associated with that engine of 4.5% due to the noise attenuation that is required."

Nordam also became active in the hushkit market several years ago, starting its Boeing 737-200 hushkit programme in 1987 in conjunction with P&W and Boeing, leading to certification in 1992. Major customers to date include Air New Zealand (ANZ), Lufthansa, USAir and General Electric Capital Services.

The Tulsa, Oklahoma-based company's first offering was the so-called high-gross weight (HGW) hushkit configuration, which was purchased by ANZ and Lufthansa, and was designed to offer Stage 3 compliance at the 737's maximum gross weight of 58,150kg.

The HGW has been largely superseded by the low-gross weight (LGW) configuration, which covers weights up to 57,660kg, or those 737s powered by the P&W JT8D-7, -9 and -15. Nordam is planning soon to gain LGW approval for the -17 derivative, which powers the 58,110kg HGW version of the 737-200.

While the HGW aircraft offers noise levels some 30% below those of the LGW machine, probably taking it inside any eventual Stage 4 requirement, the LGW aircraft weighs around 450kg less and is $1 million cheaper per aircraft than the HGW version.


Jack Arehart, director of marketing at Nordam's manufacturing division, says that the LGW is designed for "...carriers merely trying to meet the noise rules and be legal, and get the best operating economics out of the aircraft".

Arehart says that, from a total of around 1,000 737-200s in service, 501 were manufactured in 1980 or later, indicating a substantial fleet of aircraft which are relatively young, at around 15 years old. Nordam has so far sold kits for a total of 139 aircraft.

Of those 139 commitments, nine aircraft built in 1970 or before have been hushkitted. "No-one would have predicted that," says Arehart, pointing out that it is not only the youngest aircraft which operators are prepared to hushkit.

List price of the LGW kit is $1.8 million per aircraft, although they normally sell for around $1.5 million, says Arehart. The HGW kit costs around $2.5 million per aircraft. Although the Nordam 737-200 hushkitting programme is one of the most successful to date, that success did not come cheaply, with around $75 million having been spent on research and development.

Although hushkits are expected to have a detrimental effect on the performance of an aircraft, in terms of weight, thrust and fuel consumption, Nordam's hushkit is claimed by Arehart to help yield increased thrust during the take-off roll through to V2, or the safe climb speed.

There is indeed a thrust loss during the climb, and then weight and drag become the most important considerations, Arehart says. The LGW kit results in an increase in fuel consumption of about 1%.

Arehart believes that Europe will be a major market for the 737-200 hushkit even before Stage 2 aircraft have to be phased out, as landing fees are higher for aircraft which do not meet Stage 3 requirements. "Studies have shown that, on typical European routings, landing-fee surcharges total $175,000 to $200,000 per aircraft per year," he says. In Germany, the additional annual charges amount to around $500,000, one of the main reasons for Lufthansa being among the first customers for the 737-200 hushkit.

Another factor with which Nordam is having to cope, in its marketing efforts is the trend for airlines to sell fleets of aircraft and then lease them back. "Many carriers have chosen to do sale lease-backs, and it is very difficult as an operator to carry out a major capital modification on an aircraft you do not own. The lessor might not want to do it if no-one is going to pay for it," says the company. The result, says Arehart, is often a complex three-way negotiation, which can hinder the timing of a deal.

Rod Muddle, head of planning at British Airways, points out that the lessor would be rewarded through an increase in the residual value of the aircraft it owned. BA has itself sold and leased back 23 of its 737-200s.

"We would probably instigate that [hushkitting] in co-operation with the lessor," says Muddle. "That is one of the solutions. We are currently reviewing whether and to what extent we should hushkit [the 737-200s]."

Some 737 operators are waiting for Nordam's LGW kit for the JT8D-17 to become available before making a decision. "Everyone is waiting to see how the medium-range 737 kit turns out," says Ed Searle, manager of sales and marketing at HeavyLift Engineering, which is about to start modifying 727s with FedEx kits and 737-200s with Nordam's kit.

Nordam also expresses concern that a surge in demand for hushkits may occur towards the end of the century, as some airlines delay hushkitting as long as possible. Arehart says: "We cannot produce the world's requirements in one month. It is an issue we are trying to convey with the industry - we've got to spread this thing out."


While Nordam has attempted to corner the 737 market, it is FedEx Aviation Services which has targeted the 727, with Stage 3 kits certificated for all 727-100s and -200s, supporting take-off weights of up to 90,570kg.

It offers two basic versions of the kit: a "light take-off-weight kit" for 727-100s and JT8D-7-powered -200s, and a "heavyweight kit" for -200s fitted with more powerful versions of the JT8D. The programme is well advanced, with 38 customers - including FedEx itself - having ordered 291 shipsets, of which 181 have been delivered. Delta Airlines is one of the biggest customers, with 58 firm orders and a further 52 options.

Phillip Blum, manager of marketing at FedEx Aviation Services, believes that the programme's success to date is because 727s are still economic to fly when the cost of new aircraft is taken into account. "It's really driven by the economics of the 727," he says. "Comparing the operating and ownership costs with a new aircraft, the 727 will provide unit capacity at a lower cost," he adds.

Blum also believes that many operators are not hushkitting just to satisfy the regulatory requirements. "Some operators are choosing to hushkit early because of noise curfews at airports," he says.

List prices, excluding installation, are $1.8 million for the 727-100 kit, $1.9 million for the 727-200 light take-off-weight kit and $2.5 million for the -200 heavy-weight kit.

FedEx claims that, for both kits, there is "no change in thrust performance at any throttle setting". Extra airframe weight totals 240kg for the light kit, and about 410kg for the heavy kit.

The heavyweight kit may lead to higher fuel consumption on shorter flights, however. FedEx says: "A block fuel-burn increase of 0.5% may be encountered on stage lengths under 500nm [925km]."

Meanwhile, there is an increasing amount of interest in hushkitting emerging from the corporate-aviation sector. According to HeavyLift's Searle, it is the company's existing corporate customers which are "indicating most interest" in hushkitting, and the company has won commitments for the modification of two corporate 727s and three 737s. Although there are relatively few 727s still flying with Europe's major airlines, "...there are quite a number of executive and passenger 727s operating in Europe", says Searle.

Searle has also held discussions with airlines, however, and sees a "very large" potential market for 737 hushkits, particularly from charter operators. "Nearly all larger operators are leasing aircraft these days," adds Searle. "It is the leasing companies I'm talking to as well as the operators."

Source: Flight International