Drill eighteen thousand times
A major structural repair of an Airbus A321neo
Sometimes small accidents have big consequences. The repair of the Airbus A321 neo of Ural Airlines was an absolute novelty - even for us. For the first time we - as a MRO Provider - replaced an unprepared "naked" skin panel. Even for our experienced colleagues in Frankfurt, this was a real masterpiece. It was only possible because all the people involved worked well together under difficult circumstances for a long time.
Here is the story:
December 2020, Frankfurt-Airport:
In the evening, an apron tug hits the lower fuselage structure of an Airbus A321neo of Ural Airlines from Ekaterinburg. It is a leased aircraft that is still relatively new. Ural Airways immediately contacted us to examine the possibility of carrying out repairs. After extensive negotiations, the work was finally able to begin. Although the extent of the damage would allow a minor repair, the leasing company requested a repair that would return the aircraft to its delivery condition. This means replacing the entire structural panel and the damaged fuselage structure underneath.
The damaged "skin panel" is one of the largest on the entire aircraft, measuring 11.8 meters long by 2.2 meters wide. This makes the extent of the structural repair exceptionally large. To replace the panel, about 18,000 rivetes have to be removed and then all the holes have to be transferred to the new skin panel.
In order to be able to carry out the repair at all, quite a bit of preparation was necessary. With a great deal of know-how, our colleagues in Frankfurt ensured that all the necessary equipment and tools were delivered on time. For example, 8,000 additional skin pins had to be procured for tacking the panel alone.
A matter of waiting
Airbus had to manufacture and deliver the required panel first. In mid-January work began on removing various add-on parts to expose the work area. In addition, the paint had to be removed from the areas of the rivet rows. This task was taken over by colleagues from the Lufthansa Airline paint shop, who carried out the stripping of the paint under subcontract. At the end of January, they were able to start drilling out the first rivet. It took two weeks to remove all 18,000 fasteners and separate the damaged panel from the aircraft.
The next step was to repair the damaged supporting structure, known as frames and stringers. To ensure that work could continue without interruption in the event of any repair discrepancies, an Airbus engineer was on site on behalf of the customer to immediately advance any necessary clarifications with Airbus Engineering.
A great challenge
The time to tack the new panel in its future place for the first time and to start taking over the drilling and cutouts. This was all the more difficult as it was a "naked" panel with only a few pilot holes.
“The biggest challenge was to maintain a high level of concentration in the team and myself every day over the long processing period of 11 weeks. Only in this way were we able to process the 18,000 boreholes almost without a single error. The team did a great job and in the end I am happy that everything worked out so well.”
Walter Herzel, aircraft engineer
The panel was brought to the aircraft for final "wet" installation - that is, with sealant previously applied to the structure. By the end of March, the 18,000 fasteners had to be installed, the majority of which were solid fasteners that had to be driven with a riveting hammer. However, there was also a considerable proportion of so-called "Hi-Loks", which are fitting rivets that have to be screwed in with the aid of a hexagon socket wrench.
On April 6, the structural work was successfully completed. Immediately, the installation of the various parts previously removed could begin, followed by the inspection and testing of all systems involved. The final step was the painting, which was applied using the spray-paint method. This was another challenge requiring special work and safety regulations. This last hurdle, too, was successfully overcome thanks to outstanding cross-divisional cooperation, enabling our customer to take his repaired aircraft back into flight on April 19.