skywagon8a
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This came from the FAA today and is applicable to twin Cessnas. While this does not apply to Cubs it has enough importance that you all ought to be aware. It also may apply to some of your "other" planes. In addition to the mentioned jamming issue this could also be a cause for a very serious flutter incident. This from someone who has had personal experience with a trim tab push rod failure.
-- FAASafety.gov ------
Not all bolts are created equal
Notice Number: NOTC9804
Proper maintenance in aviation is so crucial to safe operation and so well-established that it almost goes without saying. But a person could easily make a mistake in assuming that all maintenance is of equal importance. Much like that quote from Syndrome of The Incredibles, “And when everyone’s super, no one will be,” if all maintenance is assigned equal importance, then truly critical items could fail to get the attention they need.
FAA airworthiness directive (AD) 2016-17-08 “Elevator Tab Control System” is a case in point. That AD mandates repetitive inspections and prohibits reuse of attachment fasteners on the elevator trim tab push-pull rod. Certainly every bolt on a plane is important, but for the airplanes listed on that AD, these bolts are more important than most.
In particular, the forward bolt that attaches the push-pull rod to the actuator merits special attention. For starters, it is recessed within the elevator and not readily visible, unlike the aft bolt that connects the push-pull rod to the trim tab. A pre-flight check of the tab might only amount to wiggling it a bit to check for free play. If the bolt was present but missing the nut and cotter pin, such a check wouldn’t detect anything wrong. However, it would only be a matter of time before the bolt worked its way free. The AD mandates repetitive inspections to make sure the hardware gets thoroughly checked at least occasionally.
If this bolt comes free, the push-pull rod and elevator trim tab will freely move as a unit. If the tab rises high enough, the free end of the rod will clear the spar cut-out. At this point, the end of the rod is likely to drop and jam against the spar, resulting in the trim tab becoming fixed in an airplane nose-down condition well beyond the normal limits of travel.
There have been several accidents over the years attributed to this condition. Out of seven events documented by the NTSB, five resulted in fatal crashes. The other two both occurred shortly after takeoff and the pilots were able to make hard landings that resulted in substantial damage to the airplanes. NTSB accident number ERA17LA329 was the most recent. The bolt was located in the elevator, but the nut and cotter pin were not found. The airplane had recently undergone maintenance and paintwork.
Accordingly, the AD prohibits the reuse of any attachment fasteners on the push-pull rod to ensure these attachment points are as robust as possible. That prohibition includes the bolt, washer, castellated self-locking nut, and cotter pin. So, for example, if the attachment hardware is removed to facilitate removal of the elevator, such as for painting and balancing, new hardware is required.
Following release of the AD, some industry media articles were published to discuss different aspects of this issue. Here are two that might be of interest for further reading.
NEW AD on elevator trim hardware affects all Twin Cessnas by Tony Saxton, Director of Tech Support
https://www.twincessna.org/pdf/Trim AD Article April 16.pdf
Tales of woe (Whoa! This isn’t an Inspection) by Mike Busch
https://www.savvyaviation.com/wp-co..._2016-10_tales-of-woe-(not-an-inspection).pdf
Indeed, not all bolts are created equal. Pay attention to this one!
For more information please contact:
Adam Hein, Aerospace EngineerWichita ACO BranchAdam.Hein@faa.gov
-- FAASafety.gov ------
Not all bolts are created equal
Notice Number: NOTC9804
Proper maintenance in aviation is so crucial to safe operation and so well-established that it almost goes without saying. But a person could easily make a mistake in assuming that all maintenance is of equal importance. Much like that quote from Syndrome of The Incredibles, “And when everyone’s super, no one will be,” if all maintenance is assigned equal importance, then truly critical items could fail to get the attention they need.
FAA airworthiness directive (AD) 2016-17-08 “Elevator Tab Control System” is a case in point. That AD mandates repetitive inspections and prohibits reuse of attachment fasteners on the elevator trim tab push-pull rod. Certainly every bolt on a plane is important, but for the airplanes listed on that AD, these bolts are more important than most.
In particular, the forward bolt that attaches the push-pull rod to the actuator merits special attention. For starters, it is recessed within the elevator and not readily visible, unlike the aft bolt that connects the push-pull rod to the trim tab. A pre-flight check of the tab might only amount to wiggling it a bit to check for free play. If the bolt was present but missing the nut and cotter pin, such a check wouldn’t detect anything wrong. However, it would only be a matter of time before the bolt worked its way free. The AD mandates repetitive inspections to make sure the hardware gets thoroughly checked at least occasionally.
If this bolt comes free, the push-pull rod and elevator trim tab will freely move as a unit. If the tab rises high enough, the free end of the rod will clear the spar cut-out. At this point, the end of the rod is likely to drop and jam against the spar, resulting in the trim tab becoming fixed in an airplane nose-down condition well beyond the normal limits of travel.
There have been several accidents over the years attributed to this condition. Out of seven events documented by the NTSB, five resulted in fatal crashes. The other two both occurred shortly after takeoff and the pilots were able to make hard landings that resulted in substantial damage to the airplanes. NTSB accident number ERA17LA329 was the most recent. The bolt was located in the elevator, but the nut and cotter pin were not found. The airplane had recently undergone maintenance and paintwork.
Accordingly, the AD prohibits the reuse of any attachment fasteners on the push-pull rod to ensure these attachment points are as robust as possible. That prohibition includes the bolt, washer, castellated self-locking nut, and cotter pin. So, for example, if the attachment hardware is removed to facilitate removal of the elevator, such as for painting and balancing, new hardware is required.
Following release of the AD, some industry media articles were published to discuss different aspects of this issue. Here are two that might be of interest for further reading.
NEW AD on elevator trim hardware affects all Twin Cessnas by Tony Saxton, Director of Tech Support
https://www.twincessna.org/pdf/Trim AD Article April 16.pdf
Tales of woe (Whoa! This isn’t an Inspection) by Mike Busch
https://www.savvyaviation.com/wp-co..._2016-10_tales-of-woe-(not-an-inspection).pdf
Indeed, not all bolts are created equal. Pay attention to this one!
For more information please contact:
Adam Hein, Aerospace EngineerWichita ACO BranchAdam.Hein@faa.gov
