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  • When 767 Bellcrank ADs Were News
    Posted by Sean Broderick 4:50 PM on Jan 27, 2014

    The most interesting aspect of an otherwise unremarkable FAA mandate on Boeing 767 elevator bellcrank assemblies that's getting a lot of attention is how the original problem came to light.

    The directive, issued today, is the latest in a series of FAA orders addressing issues with the bellcranks, which are key components that translate control column inputs into elevator movements. The issue hasn't been tied to any in-service incidents, but its discovery came during the probe of one of the more infamous NTSB investigations ever conducted: the October 31, 1999 crash of EgyptAir Flight 990.

    NTSB's full report includes a painstakingly detailed explanation of the bellcrank issues (including the diagram below), which came to light in early 2000. The simple explanation: while digging for explanations as to how Flight 990, en route from JFK to Cairo, went from a routine cruise at FL 330 to hitting the Atlantic just off the coast of Nantucket in less than one minute, Boeing discovered that failed shear rivets in the assemblies could evade the manufacturer's routine inspection procedure. Operators were ordered to perform alternative checks, which turned up more instances of latent failures. 


    blog post photo

    In theory, Boeing and NTSB found a combination of latent failures could jam a 767's elevator, which--as FAA explained in a March 2001 emergency airworthiness directive (AD)--"could result in reduced controllability of the airplane."

    Though the issue hadn't (and still hasn't) ever been linked to an in-service incident, EgyptAir pointed to the revelations as a plausible explanation for what happened onboard Flight 990. NTSB and Boeing tested every possible elevator failure scenario that could explain what happened to Flight 990, including several bellcrank-related ones. Their determination: nothing suggested by the evidence pulled from the Atlantic in the crash's aftermath would have prevented seasoned pilots, like the ones on Flight 990, from recovering their aircraft.

    While some (including, a trip deep into the paid archives shows, yours truly) pointed to possible links between the findings and the accident, FAA's directives on the issue--the new mandate replaces three dating from the EgyptAir 990 probe days--were careful to ensure perspective was maintained.

    "The FAA has received no factual information that indicates that this condition is related to an accident involving a Boeing Model 767 series airplane that occurred off the coast of Massachusetts," the agency noted in each of the directives. "The cause of that accident is still under investigation."

    NTSB eventually ruled out mechanical failure. The board's final report, adopted in March 2002, features one of the most carefully constructed conclusions ever published by the usually plain-speaking agency:

    ...the probable cause of the EgyptAir flight 990 accident is the airplane's departure from normal cruise flight and subsequent impact with the Atlantic Ocean as a result of the relief first officer's flight control inputs. The reason for the relief first officer's actions was not determined. 

    Though NTSB's analysis doesn't include the phrase "deliberate act," the board's message was received. From EgyptAir's comments on a draft of NTSB's final report:

    NTSB’s conclusion that the probable cause of the accident is the deliberate action of the relief First Officer is not supported by any evidence of intent or motive that would explain the First Officer’s alleged conduct. Indeed, the NTSB omits any discussion of motive and intent and of the facts in the record that squarely contradict a theory of deliberate pilot action. Equally, if not more disturbing, is the NTSB’s total disregard of the relevance of the unequivocal evidence of either sheared or deformed bellcrank rivets, not only on EgyptAir 990, but also on other Boeing 767 aircraft.

    The newest AD mandates work that Boeing recommended back in 2007 and is largely being done, a fact that United--one of only three commenters on FAA's draft of the rule, published 10 months ago--points out.

    "Effectively we are complying with the proposed rule, and other airlines may also be, for safety and other reasons," United told FAA. "For United and other airlines, there may be no benefit for a new superseding AD."

    Delta and the American/US Airways combination, which operate the largest 767 fleets in the world, didn't bother to weigh in at all.

    Meanwhile, the newest directive doesn't reference any in-service incident, EgyptAir, or any accident off the coast of Massachusetts or anywhere else. 

    This time around, it seems, FAA left out the story's best part.

    Tags: om99, tw99

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