Narrative:

Service bulletin; detail 'left' and to install rivet 4-5. In accomplishing this service bulletin on aircraft; I was asked by another mechanic why we were drilling out 4-4 rivets only to replace it with another one of the same diameter; but longer length. Upon further review we discovered the part number was 4-5a is a half length rivet. Supplemental information from acn 730660: while performing the heavy weight modification to aircraft; we realized we may have inadvertently installed a rivet part number 4-5 instead of the 4-5a. Contributing factors may have been the service bulletin made no mention of over-sizing holes and as a norm we have never used a half size rivet such as the 4-5a part number. Common understanding of what we normally install in emb aircraft is the last 2 digits of the part number is the diameter then the length. Example: 4-4 is a size 4 diameter and a size 4 length. The 4-5a; 5 being the diameter and the 4-5 being the length is very uncommon to the normal rivets used here. Supplemental information from acn 730683: I inspected the work after the rivets between frames 45 and 46 left and right were installed and did not notice that incorrect rivets were installed by the technicians during the work. The blueprints show that a dash 5 diameter rivet to be installed but apparently a dash 4 diameter rivet was installed and I did not notice the difference after the rivet was worked. Revise the service bulletin to reflect the requirement to oversize the original rivet holes. Callback conversation with reporter acn 730654 revealed the following information: reporter stated all air carrier's emb-145 aircraft are affected by this service bulletin. Accomplishment of this service bulletin will allow for heavier weight carrying capacity of this type aircraft. Neither the service bulletin; nor the engineering order; made any reference to a requirement to oversize the existing fastener hole to accommodate the replacement fastener. These include countersunk rivets for securing a support angle for the stringers to fuselage frames and external skin. Reporter also stated that as a result of the increased maintenance work driven by this service bulletin; maintenance workers with less airframe structures experience have been brought in to help complete the work. The lack of any reference to oversize the fastener holes contributed to the misunderstanding and misreading of fastener length vs diameter requirement called out in this service bulletin. Once rivet installed; inspection cannot visually determine if hole was oversized.

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Original NASA ASRS Text

Title: EMB-145 ACFT SERVICE BULLETIN REMOVE/REPLACE SPECIFIC FUSE FRAME FASTENERS. OVER-SIZING HOLES REQUIRED; BUT NOT NOTED.

Narrative: SVC BULLETIN; DETAIL 'L' AND TO INSTALL RIVET 4-5. IN ACCOMPLISHING THIS SVC BULLETIN ON ACFT; I WAS ASKED BY ANOTHER MECH WHY WE WERE DRILLING OUT 4-4 RIVETS ONLY TO REPLACE IT WITH ANOTHER ONE OF THE SAME DIAMETER; BUT LONGER LENGTH. UPON FURTHER REVIEW WE DISCOVERED THE PART NUMBER WAS 4-5A IS A HALF LENGTH RIVET. SUPPLEMENTAL INFO FROM ACN 730660: WHILE PERFORMING THE HVY WT MODIFICATION TO ACFT; WE REALIZED WE MAY HAVE INADVERTENTLY INSTALLED A RIVET PART NUMBER 4-5 INSTEAD OF THE 4-5A. CONTRIBUTING FACTORS MAY HAVE BEEN THE SVC BULLETIN MADE NO MENTION OF OVER-SIZING HOLES AND AS A NORM WE HAVE NEVER USED A HALF SIZE RIVET SUCH AS THE 4-5A PART NUMBER. COMMON UNDERSTANDING OF WHAT WE NORMALLY INSTALL IN EMB ACFT IS THE LAST 2 DIGITS OF THE PART NUMBER IS THE DIAMETER THEN THE LENGTH. EXAMPLE: 4-4 IS A SIZE 4 DIAMETER AND A SIZE 4 LENGTH. THE 4-5A; 5 BEING THE DIAMETER AND THE 4-5 BEING THE LENGTH IS VERY UNCOMMON TO THE NORMAL RIVETS USED HERE. SUPPLEMENTAL INFO FROM ACN 730683: I INSPECTED THE WORK AFTER THE RIVETS BTWN FRAMES 45 AND 46 L AND R WERE INSTALLED AND DID NOT NOTICE THAT INCORRECT RIVETS WERE INSTALLED BY THE TECHNICIANS DURING THE WORK. THE BLUEPRINTS SHOW THAT A DASH 5 DIAMETER RIVET TO BE INSTALLED BUT APPARENTLY A DASH 4 DIAMETER RIVET WAS INSTALLED AND I DID NOT NOTICE THE DIFFERENCE AFTER THE RIVET WAS WORKED. REVISE THE SVC BULLETIN TO REFLECT THE REQUIREMENT TO OVERSIZE THE ORIGINAL RIVET HOLES. CALLBACK CONVERSATION WITH RPTR ACN 730654 REVEALED THE FOLLOWING INFO: REPORTER STATED ALL ACR'S EMB-145 ACFT ARE AFFECTED BY THIS SERVICE BULLETIN. ACCOMPLISHMENT OF THIS SERVICE BULLETIN WILL ALLOW FOR HEAVIER WEIGHT CARRYING CAPACITY OF THIS TYPE ACFT. NEITHER THE SERVICE BULLETIN; NOR THE ENGINEERING ORDER; MADE ANY REFERENCE TO A REQUIREMENT TO OVERSIZE THE EXISTING FASTENER HOLE TO ACCOMMODATE THE REPLACEMENT FASTENER. THESE INCLUDE COUNTERSUNK RIVETS FOR SECURING A SUPPORT ANGLE FOR THE STRINGERS TO FUSELAGE FRAMES AND EXTERNAL SKIN. REPORTER ALSO STATED THAT AS A RESULT OF THE INCREASED MAINTENANCE WORK DRIVEN BY THIS SERVICE BULLETIN; MAINTENANCE WORKERS WITH LESS AIRFRAME STRUCTURES EXPERIENCE HAVE BEEN BROUGHT IN TO HELP COMPLETE THE WORK. THE LACK OF ANY REFERENCE TO OVERSIZE THE FASTENER HOLES CONTRIBUTED TO THE MISUNDERSTANDING AND MISREADING OF FASTENER LENGTH VS DIAMETER REQUIREMENT CALLED OUT IN THIS SERVICE BULLETIN. ONCE RIVET INSTALLED; INSPECTION CANNOT VISUALLY DETERMINE IF HOLE WAS OVERSIZED.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.