Posted by: Bryan Anderson
RepairMaps Keeps Tabs on the Total Doubler Area
One of the less endearing aspects of maintaining and operating the 737 Classics is the requirement to constantly monitor the total area of installed doublers on the fuselage. Certain restrictions are applied to the aircraft for “operation with extensive fuselage repairs” when the combined area of repairs reaches a certain threshold. From the 737-200 SRM:
As a general rule, only certain SRM repairs include this restriction language. For example, the 737-200 SRM includes only fuselage skin repairs performed per 53-30-3, Figure 46, 48 and 49:
Figure 49 Applicability section muddies the waters a bit in this way:
Note the difference in the two flag notes. One implies only the three key figures and the other implies a much broader category of repairs to be included.
Additionally, some service bulletins, such as the lap seam repair/modification SB, contain restrictions pertinent to the external repair members installed by them. Lastly, when the cumulative total of external repairs reaches a certain point, the aircraft must be submitted to Boeing for aerodynamic analysis.
As you can see, there can be differing definitions and/or interpretations of what should be included in the aircraft area calculation. My team recently worked a project handling several aircraft that had extensive fuselage repairs to the point that submittal for analysis was required. We sought Boeing’s advice regarding what should be included in the submittal for analysis, and asked them if they wished to see only repairs performed by the specified repair figures or all external repairs. Their answer at the time was: “Yes, when Boeing asks for a survey of existing fuselage repairs, we want ALL repairs included, whether done according to SRM or by specific instructions from Boeing.” We've interpreted this to mean the area of any doubler on the aircraft that is exposed to the airflow. This is consistent with the flag note language shown above and is the conservative approach. It should be noted that the sum of repair area allowed has doubled in more recent revisions of the SRM, so the likelihood of actually arriving there is remote. The requirement to track area totals accurately and apply penalties does remain mandated, however.
RepairMaps gives you a very convenient set of tools to easily comply with this requirement. First is the area attribute:
The system will calculate square and round area values for you as you enter dimensions and shape (the area attribute does not auto-fill if ‘Other’ is selected). If the calculated area is not pertinent for some reason (for example part of the doubler resides under a fairing), you may overwrite the system generated value with a more representative one.
The second part of this attribute is the selection to “Include area in doubler total” selection:
By selecting ‘Yes,’ the value shown in the area attribute is added to the aircraft’s total doubler area. The area in any Tracked Item is added to the aircraft total only if the Tracked Item is Finalized. This ensures the value has been reviewed and vetted by the participants in the RepairMaps Two-Party Workflow system.
The aircraft total doubler area value is made available in a couple different ways. The most convenient is on the Dashboard in the center grid:
A list of all the TIs that make up the doubler total for a particular aircraft is available by clicking the info button next to the total:
The total area for a given aircraft is also available by clicking through to the Details area for any aircraft.
And then selecting the Aircraft Stats tab in that grouping.
While area tracking can be a troublesome task, RepairMaps provides the tools necessary to comply with the requirements quickly and easily. The required information is readily available to those that need it instantaneously by simply accessing one’s account.