Hush Job

Special "hush kits" make airplanes quieter. Do they also make them more dangerous?

Editor's Note:

For years, public clamor over noise at the Minneapolis/St. Paul Airport has been nearly as deafening as the roar of a departing jet. Now there are indications that a technological fix to the problem--use of federally approved kits to "hush" the noise of DC-9 engines--may be a problem itself. An investigation by the alternative weekly Nashville Scene (excerpted below) has found that a consultant for the sole manufacturer of the DC-9 hush kits reports that faulty construction and installation may make the kits a dangerous hazard. The biggest user of the kits? Eagan-based Northwest Airlines, which uses 83 on their fleet of 179 DC-9s.

Last summer, aviation consultant Peter M. Friedman was hired to inspect parts being installed on DC-9 airplanes at a Trans World Airlines maintenance facility in Kansas City, Missouri. Friedman's specific objective was to perform a routine audit of the airplane's "hush kits," the devices used to muffle engine noise. The kits had been designed and sold by ABS Partnership, a low-profile, privately held company based in Sparks, Nevada. It was ABS that had hired Friedman to make certain the hush kits were of top quality and were being installed properly.

Cory Rasmussen

Friedman's credentials indicated he was the right man for the job. The Federal Aviation Administration (FAA) has designated him one of its "manufacturing inspection representatives," and he is certified by the American Society for Quality Control as a "quality auditor." In some sectors of the aviation industry, Friedman has a reputation as a relentless safety hound. Sometimes his critics describe him as a stickler for technical violations. But no one seems to doubt his knowledge of aviation-safety issues.

ABS had hired Friedman on a "confidential basis," meaning that he could only divulge his findings to the company. Nevertheless, his reports, copies of which have been obtained by the Nashville Scene, were so explosive, and his safety concerns so troubling, that they created a storm of controversy in aviation-safety circles.

Jim Frisbee, who was manager of quality assurance at Northwest Airlines until 1992 and who now works as an international aviation consultant, reviewed the Friedman report at the Scene's request. He says it raises "serious safety problems. Depending on the circumstances, the FAA may well have to ground these planes."

For airline passengers, Friedman's report is chilling. The document warns of numerous problems that could arise from the hush kits and "affect safety of flight" for the DC-9, one of the most common models flown by commercial airlines (U.S. airlines own almost 600 DC-9s, and it is estimated that at least one-third of them are flying with ABS hush kits). The report recommends that ABS take corrective action before a "catastrophic incident" occurs.

Specifically, Friedman's audit says the hush kit sold by ABS simply does not fit properly onto the back of the Pratt & Whitney engine that powers the DC-9. What's more, the report says, engineers and mechanics for each airline must figure out how to attach the kit's parts without the benefit of proper plans or workable instruction manuals. That state of affairs, which is in blatant violation of FAA regulations, increases the likelihood that mechanics will make mistakes when installing the hush kits.

If there is a bad fit, Friedman's report warns, the doors encasing the engine's tailpipe could blow open in midflight. That would be bad news for the DC-9, which typically cruises at speeds around 500 miles per hour. If the doors were ripped open, one of the plane's engines would continue to thrust the plane forward, while the other engine would do just the opposite. In that eventuality, the DC-9 could roll over onto its back, corkscrew down, and crash.

There's another terrifying scenario. If not fitted properly, one of the tailpipe doors could fly free and knock off the plane's tail, which sits just behind the two engines. If that happened in midflight, aviation-safety experts say, a crash would be virtually inevitable.

Friedman's report on the ABS hush kits also warns of mislabeled and obsolete parts, incomplete data, and miscalibrated equipment. It also charges that airline personnel have received "absolutely no" training in inspecting the hush kits before they are installed. The report warns that flight safety may be compromised by "cracked links and hinges," as well as by inadequate installation instructions. Friedman's report also notes that he inspected the ABS door assemblies that encase the engine's tailpipe, and found "each one [was] different from the next." Under the terms of his confidentiality agreement, Friedman declined all comment about his dealings with ABS.

ABS, however, says there is no problem with the kits. In February 1997 a company spokesman told the Scene that it was aware of no "safety of flight" hazards stemming from its hush kits. At that time the firm had already been in possession of Friedman's audit report for five months. In a later letter to the Scene, ABS says the firm is "absolutely certain" of the hush kits' safety. In the same letter, the company says it has been "open and cooperative with the FAA, the DOT, our customers, and the media. We are proud of our product, its in-service record, the professionalism, dedication, and diligence of the team we have in place to support our product and comply with all regulatory requirements."

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