FAA to Issue 'Emergency Airworthiness Directive' On Boeing 767 Elevator Control System
WASHINGTON, Aug. 15 /PRNewswire/ -- The Boeing 767 elevator control
system, suspected by Egyptian investigators and U.S. aviation experts as a
possible cause of the EgyptAir Flight 990 crash last October, is the target of
a Federal Aviation Administration (FAA) "emergency airworthiness directive" to
all airlines.
The FAA is acting following a joint investigation with Boeing that
uncovered at least 11 instances of sheared rivets in the critical elevator
control system aboard 767 aircraft.
The FAA inquiry was initiated following
receipt of a June 4, 2000 letter to Administrator Jane Garvey from the head of
the Egyptian Civil Aviation Authority, providing information on the exact same
problem, exposed during the EgyptAir Flight 990 investigation.
A bulletin from the Boeing Service Engineering Customer Support Group was
prepared in mid-July and made public to air carriers and airworthiness
authorities on July 31.
The National Transportation Safety Board (NTSB) opened the EgyptAir 990
docket last Friday, August 11, providing "factual information" on the crash.
The "emergency airworthiness directive" calls for safety inspections of
the bell cranks, a part of the critical elevator control system, located on
the tail of an aircraft. The elevators control the upward or downward
movement of the nose of a plane.
Egyptian investigators and U.S. aviation experts probing the EgyptAir
Flight 990 accident have pointed to sheared rivets as evidence of a jam in the
elevator control system, causing the plane to pitch down. A power control
unit from the right elevator on the tail of EgyptAir Flight 990 showed several
anomalies and unexplained damage when it was examined.
EgyptAir Flight 990 crashed off Nantucket en route from New York's John F.
Kennedy International Airport to Cairo, Egypt.
A team of Egyptian experts has been working as accredited members of the
NTSB investigation since shortly after the accident. Dispatched by the
Egyptian Civil Aviation Authority and EgyptAir, they have been assisted by a
number of U.S. aviation and technical experts.
EgyptAir, founded in 1932, is a founding member of the International Civil
Aviation Organization (ICAO) and the International Airline Transport
Association (IATA). EgyptAir flies the latest generation of aircraft on
routes around the world.
Congratulations, you can locate a directive without any understanding of what it means. Sorry, let me rephrase that. Congratulations, you can locate a news article written to sell newspapers that mentions an airworthiness directive without any understanding of what an airworthiness directive means, or what this one in specific means (I would be willing to bet money you didn't even read the actual AD it mentions which would give background on why it's issued).
During analysis of a crash parts are recovered and looked at. At the first hint of a possible mechanical problem, directives are issued to "inspect" for fault. Do you know what airlines do if they find fault? They immediately tell the manufacturer. In some ways, you can look at it as fact finding. The bellcranks showed sheared shear rivets (again, that's what shear rivets are for, hence why they have the word "shear" in them) and issued a directive to have them looked at. If all the airlines are reported sheared rivets on 767 bellcranks, that helps investigators narrow the scope and gives the manufacturer a kick in the ass to repair the issue. Turns out the probing didn't return much of value. Yes, some aircraft showed shearing in the bellcranks. What you fail to consider is the fact that since the directive was issued, Boeing had determined the aircraft performed as expected - that shearing of shear rivets (again, what they're designed to do) doesn't render the aircraft uncontrollable. Sheered bellcrank rivets might require more power on the control systems to move the systems, power the autopilot lacks, but a pilot is still able to control the aircraft through the linkage system with sheared bellcrank shear rivets. Furthermore, that directive was issued in 2000. Further analysis and investigation determined the cause for the sheared shear rivets in the EgyptAir 990 case to be differential control pressure, the only answer to why some are sheared in one direction and the rest in the other, which is all explained in the report the was issued in 2002. Additionally, a sheared bellcrank will yield a certain flight profile, a profile that doesn't match the EgyptAir 990 case. A failure in the PCA or bellcranks will cause a near-neutral elevator condition after the initial nose-over, not a hard-over as ECAA claims was the cause of 990's crash. This was determined only after extensive testing. In fact, if you actually read the entire NTSB report, you'll see that not only does the condition return to near neutral, the aircraft is designed to be aerodynamically stable and if no pilot input is made at all, will begin recovery on it's own, even without autopilot turned on, within 20 seconds. It's a feature of how aircraft work. If you trim a stable aircraft for level flight, airspeed will take care of everything. If the aircraft is trimmed and speeds up for any reason, the nose comes up and it gently oscillates itself to an attitude that will result in the same airspeed. Likewise if it slows down, the nose will drop and it will gently oscillate itself to an attitude to maintain that speed. So in a trimmed aircraft, which both autopilots and real pilots configure for, shearing in the bell cranks MAY nose the aircraft into a gentle dive initially, and within 20 seconds, as the airspeed starts to climb a few knots, air pressure on the control surfaces will automatically pull the nose up, reducing the airspeed. Eventually the airspeed will be slower than it was in trimmed, level flight, and the nose will start to pitch down again to speed up. Each time it oscillates, the speed variation from trimmed level flight is less, until the aircraft finds itself back in an attitude that maintains the trimmed speed.
The directive operated on the assumption that shear in the bellcranks caused a hardover condition. It turns out that it doesn't. It turns out that it was designed not to. The ECAA, based on reports from EgyptAir, sent information to the NTSB saying that hardovers were noted from shearing in the bellcrank shear rivets. Further investigation has determined that's not the case. ECAA has never acknowledged those findings, but they've never disputed them either, except to maintain the position that it was the "likely" cause of 990's crash. In any case, "inspection" is what's noted in the directive, not "replacement". EDIT: I should clarify here. They are ordered replaced if found faulty, but the AD doesn't say "replace all bellcranks with the following part number with these new ones". END EDIT. The crux of the issue is that Boeing designed these systems to be inspected, but determined that routine inspections didn't include checking these shear rivets. Alternative maintenance instructions were subsequently issued to ensure that all bellcranks are inspected on a regular basis. A new AD was issued in 2001 with even more revised instructions after a report was received that an elevator drooped during a routine walk-around check of an aircraft. It isn't a failure, but pilots, being safety conscious that we are, since if something is wrong it isn't Boeing, the FAA or the maintenance crews that die but us, snag them, rendering the aircraft unusable until the snag is resolved. Under pressure, because now the airline has a 767 sitting on the ground that a pilot refuses to fly and maintenance has no directive to fix, Boeing issues a directive to fix it. In 2001, because reports were coming in that the rivets were "shearing" without warning (meaning maintenance was finding them in the inspections detailed in the previous AD), Boeing issued a new directive to test them regularly to look specifically for shear. In 2007, after thousands and thousands of flights by 767 with not a single case of failure being attributed to unrecoverable failure, Boeing issues a new directive. Why? They told people to look for sheer rivet failures and now they're tired of the reports coming in. Given that sheared shear rivets don't actually disconnect the linkages or change the properties of the elevator control system, they order any bellcrank with sheared shear rivets replaced with a new part that doesn't contain shear rivets at all. In other words, that built a safety feature that's overruled by other safety features and is, essentially, pointless, but since it generates so much paperwork, they're removing it from service. I think they summarized it nicely from the latest AD:
http://www.regulations.gov/contentS...228dcd&disposition=attachment&contentType=pdf
"A detailed design review found that the override device incorporated into the elevator PCA input rod assembly provides protection against malfunctions and non-normal PCA operation. This design review also found that the shear rivets are not needed."
It should also be noted that several directives were issued by other authorities (outside the US the FAA has no bearing). Australia's AD was accompanied by the following explanation:
"The FAA has received reports that elevator bellcrank assemblies with failed shear rivets have been found on
three Model 767 aircraft. On one aircraft, the failed shear rivets were found in both the left inboard and left centre power control actuator bellcrank assemblies. Failure of two bellcrank assemblies on one side can result in that single surface moving to a hardover position independent of pilot command resulting in a significant pitch upset
recoverable by the crew."
Note my emphasis. I didn't emphasize hardover since,by definition, it's not a hardover if it's recoverable. Simple case of a politician writing a report with wording he's heard and no understanding of that wording. An aircraft that entered service in 1981 found that a grand total of three (3) aircraft in 21 years exhibited this issue. Also note the phrase "recoverable by the crew". It was issued several months after the FAA one, which means it includes information that wasn't available to the FAA. And before you bring it up, in the final AD issued in 2007, Boeing, not wanting to lose business with MSR and other large airlines in the Middle East that believe the FAA report is incomplete they included the phrase "possible loss of control" even though, to date, not a single case (except EgyptAir 990 according to you and "maybe" according the MSR who say failed bellcrank is only one of several "possible causes" yet continued to fly 767's without them being 'repaired' to avoid this problem) of bellcrank shear failure has been reported as causing a loss of control. At no point has anyone "hid" or "covered up" anything, and yet MSR STILL FLIES 767s. This unsafe machine with unsafe mechanism that maybe crashed their plane according to them, which for 7 years after still had the same potential. They are so convinced that this unsafe and dangerous condition existed and brought down a flight killing hundreds of people that they did what exactly? Oh right, they did absolutely nothing and continued to operate that aircraft model daily without concern. Now tell me, does that sound like an airline that almost goes bankrupt from a crash and the subsequent lawsuit, or does it sound more like some PR spin trying to cast doubt on where the blame is to win said lawsuits and maintain the trust of the flying public?
In any case, it's amazing how aviation works, huh? In the course of an investigation, they locate a possible cause, issue a directive for everyone to watch for it just in case, then continue the investigation and either prove or discount that as the cause of the crash. This doesn't prove bellcranks are faulty. What it does prove is that, contrary to the claim otherwise, the NTSB and the FAA didn't say, "Holy shit an Egyptian guy saying a prayer? Ignore everything and let's just try to prove he crashed the bastard, that dirty brown-skinned, muslim terrorist!" They looked at all possibilities seriously - seriously enough to issue an emergency directive the second they found any mechanical anomaly that they couldn't immediately explain.
But hey, good job ignoring ALL the evidence and jumping on just the ONE PIECE that backs up your theory. Good thing that, unlike you, the NTSB didn't stick to one working theory and run with it even when analysis and evidence showed it was wrong.
