As regular readers will know, BBMF C-47 Dakota ZA947 has been undergoing a ‘Major’ maintenance programme, under contract with the Aircraft Restoration Company (ARCo) at Duxford, since October 2022. It had been expected that the maintenance programme would be completed in time to allow the ‘Dak’ to be available to return to the Flight in early 2024. Unfortunately, due to considerable unscheduled emergent work, the maintenance programme is still some way from completion and the Dakota will miss most, if not all, of the forthcoming display season.
The emergent work is mainly related to a considerable amount of airframe damage and corrosion which was discovered in the inspection phase, as well as ‘wear and tear’ issues on items, such as the flying control system, that needed to be rectified. In addition, following removal of the Dakota’s outerwings, detailed inspection and non-destructive testing (NDT) of the inner to outer wing transport joints revealed cracking that required structural repairs. It is, of course, precisely to uncover such issues as these during deep-strip inspections that the ‘Major’ maintenance programmes on the BBMF historic aircraft are scheduled.
The Dakota’s port and starboard outer wings are bolted to the centre wing section via attachment angles, called transport joints. During fatigue testing of a whole Dakota wing carried out by the Douglas Aircraft Company in 1961, one of the areas that failed was the centre wing bottom skin between the front and rear spars. As a result, a Service Bulletin (SB262) was issued which introduced inspection holes drilled through reinforcing doublers, so that the bottom skin of the centre wing could be inspected for cracks when the wings were removed. During the inspection carried out on BBMF Dakota ZA947 during its current Major maintenance programme, fatigue cracking was found in these SB262 inspection holes.
Discussions on how to rectify this damage involved the BBMF Project team (PT), ARCo, Marshall Aerospace as the Design Advisor, and Boeing as the Original Equipment Manufacturer (having absorbed the Douglas Aircraft Company via McDonnell Douglas). After some of the damage and corrosion had been blended and measured for assessment, as recommended by Marshall, all the bolt holes were subjected to eddy current testing and, due to fault indications, it was decided that eight of the wing attachment angles needed to be replaced. Having procured all the attachment angles and doublers from the USA as directed by Marshall, there is concern that replacing the upper doubler on the starboard centre wing would be extremely challenging as it extends into the engine nacelle; removing the nacelle has the potential to cause irreparable damage to the wing. The BBMF Type Airworthiness Authority has proposed removing the associated attachment angle and assessing the condition of the starboard upper doubler. Then, if there is no corrosion or damage to holes or skin, the doubler could be left in situ and a new attachment angle attached. All other doublers will be replaced as per the Marshall advice. This option is currently under discussion with all stakeholders.
These additional repairs and the complications surrounding them have inevitably delayed completion of the Major on the Dakota, with the current date for the aircraft to return to Coningsby being estimated by ARCo to be September 2024. When ZA947 does return to the BBMF though it will be in the very best condition to continue flying with the Flight into the future.
