ADs, NPRMs and service bulletins

An aerospace reporter discovered a 20-year-old Boeing 747 crash near Madrid through aviation industry publications and FAA records, which revealed a potential link to the TWA Flight 800 disaster through similar fuel tank vulnerabilities. By systematically searching trade magazines, library databases, and NTSB records, the reporter obtained a detailed investigation report showing how a lightning strike ignited a fuel sensor spark, leading to catastrophic wing failure.

More plane crash sources

By Bonnie Britt The Tribune Review

On July 24, in the Seattle Times, aerospace reporter Byron Acohido wrote, "The crash of TWA Flight 800 was not the first time witnesses on the ground watched as a Boeing 747-100 burst into flames and tumbled to earth."

The story went on to describe a crash 20 years ago that drew little public attention: A former TWA 747-100 converted into a freighter for the Iranian air force - a sister ship to the one that crashed off Long Island - exploded in flight near Madrid, Spain.

How did he know that?

Hot tip

On a tip, Acohido headed to the library where he spent half a day pressing through four years of indexes on microfiche from Aviation Week & Space Technology, the industry bible.

When he didn't find the reference in the trade magazine's table of contents, he pushed through it again, 1975-1979, page by page. He found a brief reference in a column item and another reference to an FAA airworthiness directive (AD) triggered by the crash. The AD called for inspection for dangerous fuel leaks that could cause fire and explosion.

The tip was legitimate. Where were the details?

Acohido says, "It happened 20 years ago on Spanish soil. It was an Iranian jet. I assumed be impossible to confirm." Hungry for elaboration of the crash mentioned briefly in the two Av Week stories, Acohido looked up Spanish authorities. When that went no where, he called in the calvary.

"We have a great library. I asked for a universal search. The librarian found three or four references to the crash, plus a couple of remotely related clips, including excerpts from a magazine article that talked about major disasters involving large aircraft.

NTSB

"The article made reference to the National Transportation Safety Board finding implicating lightning in the Madrid crash. It turned out the NTSB and a bunch of agencies had retrieved and closely examined the wing that exploded in Madrid. A light bulb went off. There had to be an NTSB report."

Acohido checked the NTSB's Web site (www.ntsb.gov) but saw no reference to the Madrid incident or the 1976 report. He says, "You can't trust their Web site since it is not complete."

Then he went low tech. He called the records department at the agency and politely requested a copy of the report. Within 24 hours, Acohido had the 50-page report via Federal Express. The report - Special Investigation Report: Wing Failure of Boeing 747-131 near Madrid, Spain. May 9, 1976 - is available from the National Technical Information Service (U.S. Department of Commerce) in Springfield, Va.

Acohido copied it to an aircraft wing expert. The report detailed clear and compelling evidence that a moderate lightning strike (which the aircraft is designed to withstand) most likely ignited a stray spark on a fuel sensor inside a partially-full fuel tank. A small explosion followed by an intense localized fire began a sequence that led to the wing coming apart and releasing a huge ball of burning fuel less than a minute after lighting struck the wing.

"The NTSB text gives step-by-step hard evidence in very technical prose. You have to read between the lines. My wing expert and other knowledgeable sources helped me get a layman's grasp of what the report said."

Next stop, FAA

The next step was to obtain the Federal Aviation Administration's airworthiness directive from the AD database. An AD is an order from the FAA to the industry to fix a flaw in a particular model of aircraft. ADs come with deadlines. Acohido was certain an AD had been issued after the 1976 crash since the encyclopedic Av Week referred to it. Guessing there might be other fuel tank glitches, he pressed the FAA for all ADs relating to 747 fuel tank problems.

He says his newspaper is discussing building and maintaining its own database of airworthiness directives.

The FAA maintains indexes for their databases of notices of proposed rule-making and the airworthiness directives.

When you are not sure what you want, ask for the AD index to the model aircraft (i.e. 747-100 or 737-100, 200 and 300) that interests you. It contains all regulations pertaining to everything on that model that may be flawed, except what didn't get past the rule-making process.

When you know which AD you want, also ask for the electronic file on the Notice of Proposed Rule-Making (NPRM) associated with that AD. It contains the industry discussion of what went wrong, how serious the flaw is, economic factors in making a fix and logic about deadlines. An AD is a congressionally mandated FAA answer to each and every letter that makes up the NPRM file.

Contents of many items in the two databases - NPRMs and ADs - provide long satisfying looks at the process leading to orders for industry-wide fixes of known defects.

To be thorough, ask for copies of the original letters that make up the NPRM file. They reveal much more than the FAA's electronic summary of who said what in the rule-making discussion.

"From experience," Acohido says, "I know you don't just want the ADs that say a flaw must be fixed in a certain way. You also want the NPRMs since they provide the discussion and criticism of the proposed fix."

The final rule or AD gives the industry the recipe to fix the aircraft part that's flawed in general terms, typically referring to Boeing service documents for specific steps.

Service bulletins

You guessed it: the Boeing documents, called service bulletins, are another gold mine.

Says Acohido, "Deeper behind the NPRMs are the service bulletins - the manufacturer's explanation and drawings on how to make the fix. You can get them from the FAA." Doing so calls for imagination. After the TWA crash, Acohido recalls, "We physically had to go down to the FAA for the service bulletins and were stonewalled at that level."

Often the service bulletin will contain a single profound line revealing the manufacturer's logic about why a fix must be made.

ADs seeking to fix weak locks on 747 cargo doors were supported by Boeing service bulletins, which noted what could happen if a door ever came open at altitude: "It can cause rapid decompression."

Given the choice of inspecting for weak locks or installing stronger locks, many airlines procrastinated, until a cargo door came open on United Flight 811 off Hawaii in 1989. Nine passengers were sucked out a gaping hole in the fuselage during the resultant rapid decompression. The FAA then mandated stronger locks on all 747s within 30 days.

The Boeing service bulletins supporting ADs mandating inspections and fixes for leaking 747 fuel tanks note succinctly: "Leaks can cause fire."

Where besides the reticent FAA (or the manufacturer) can you find service bulletins in a hurry?

Make friends with the faculty at a college where aircraft mechanics are trained. Ask to see the data on the service bulletin database for the fixes that interest you.

When you return with it, Acohido says "Your artists will love you."

On Aug. 21, the Seattle Times ran a generous, above the fold graphic based on detailed diagrams of the 747, its wings, its fuel bays and areas prone to leaks sourced to Boeing's service bulletin.

Bold type asked: "Did fuel leak cause explosion?"

"Federal aviation and Boeing service records contain extensive documentation about where the wing and belly tanks on 747s are susceptible to leaks that can cause fire."

Bonnie Britt can be reached by e-mail at bonnieb@cris.com