Three mechanics report an MD-80 Structural Repair Manual (SRM) illustration does not accurately represent the requirement to have flush repair internal doublers pass under longerons; modified shear ties and frames for a left alternate static port external fuselage skin repair in an RVSM area.
Synopsis
Three mechanics report an MD-80 Structural Repair Manual (SRM) illustration does not accurately represent the requirement to have flush repair internal doublers pass under longerons; modified shear ties and frames for a left alternate static port external fuselage skin repair in an RVSM area.
Narrative
I performed a repair on a MD-80 aircraft at the left hand Alternate Static Port area station location 420-465; longeron 28-left to 26-left. The repair was performed per Structural Repair Manual (SRM); outlining a Flush Repair concerning the production skin overlap. This repair is called a 'brick method' pertaining to the thick internal doublers. The SRM Figure illustrates the 'bricks' terminate; or start and stop at the longerons and shear ties/frames; with continuous finger doublers running under all related structure.This repair also illustrates straps being used in the longerons. The damaged area was removed and all repair materials were verified by our Inspectors on duty as per primary structure repair; and clearance to install/begin build-up of repair. After visiting with another Mechanic after repairs were completed; we debated over the 'bricks' starting and stopping at the shear ties frames; and installing new shear ties/frames. The Mechanic showed me another similar repair being for another area; which had a better/sharper picture outlining the repair.We then looked at SRM under closer examination; we discovered the 'bricks' are supposed to pass under the shear ties/frames; with modified/repaired shear ties/frames to allow the doubler to not apply preload or stress to the repair and skin; and causing contour changes in the RVSM [skin] area. The SRM figure does not make mention of altering/modifying or performing repairs to the affected shear ties/frames. And the SRM figure does not include a view of the shear ties/frames; or a view of modified/repaired shear ties/frames. In the SRM figure; near the shear tie/frame area; the dashed/jagged lines; and fastener legend/identifying marking do not accurately represent performing this repair.
Second reporter narrative
I was involved with some of the fabrication of finger doublers on an MD-80 aircraft. I read the SRM; that's what I interpreted too [also]. I believe all the Mechanics involved read the SRM the same way. I do believe that all parts to this repair were drilled up and installed per the SRM reference to the best of our knowledge.
NASA callback
Reporter stated a flush repair was required instead of a standard scab patch because of the Reduced Vertical Separation Minimums (RVSM) airflow requirements around the alternate static ports. There are a total of two alternate static ports on the MD-80; one each for the left side and right side of the fuselage. Both ports are directly across from each other; with the right alternate located just aft of the forward cargo door.Reporter stated the MD-80 was being opened-up for routine maintenance when Inspection noticed the Citrus-Clean fluid used to clean the inner fuselage skin; frames; longerons and shear ties; was draining between the manufacturer's internal bonded skin doubler installed on the inner surface of the fuselage skin around the fuselage hole for the left alternate static port. Further inspections determined that screws for the left alternate static were too long and actually pushed against the internal bonded doubler around the static port; causing the doubler to disbond. Sometimes the internal doubler will also disbond on it's own.Reporter stated the other Mechanic he referred to had just completed a flush repair for the right alternate static port using the same MD-80 Structural Repair Manual (SRM). But the difference in clarity of the SRM illustration where the finger doublers and doublers were suppose to be positioned under the longerons; frames; modified shear ties and skin overlap were much clearer to see. That repair illustration clearly showed the doublers going beyond the skin overlaps. He believes that illustration was better because the forward cargo door frame was also involved with the right alternate static port flush repair procedure.Reporter stated that even their Engineering admitted the illustration diagrams for the left alternate static port repair were general in nature and very hard to follow. Mechanics needed the repair procedures to be specific to correctly perform the skin repair. All the MD-80's that did not have the skin doubler repair going under the longerons were repaired by installing an additional strap. Reporter stated that ironically; even thought any fuselage skin repair has to be done per RVSM requirements; only the primary staic ports are allowed to be used when in RVSM airspace; the alternate static is not.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.