An Aeronova Boeing 737-800 on behalf of Air Europa, registration EC-OBO performing flight UX-1672 from Zurich (Switzerland) to Madrid,SP (Spain), was on final approach to Madrid's runway 18L when upon extending the landing gear main wheel #2 dropped one of its torque bars, which fell onto the roof of a private house. The aircraft continued for a safe landing on runway 18L.
A subsequent inspection revealed 3 torque bars were missing, one was found in Palma Mallorca, the third is still missing.
On Oct 16th 2025 Spain's CIAIAC released their final report concluding the probable cause of the incident was:
The most likely cause of the incident is considered to be the loss of tightening torque on the No. 2 wheel torque bar fastenings, which caused the torque bar to come loose. However, during the investigation it could not be determined what caused this loss of tightening torque as it could have been due to improper or unappropriated tightening and/or improper breakaway torque of the nut to hold the tightening torque.
The CIAIAC analysed:
With the help of Safran Landing Systems, the manufacturer of the wheel, an analysis has been made of what could have caused the loss of the three torque bars on wheel No. 2. This could have been due to either a rupture of the bolts or a loss of tightening torque.
With regard to the rupture of the bolts, the CIAIAC rules out that this caused the loss of the torque bars for two reasons:
- Neither in the incident under investigation nor in the two subsequent incidents on 19 May and 8 June on wheel No. 3 of the Boeing 737 aircraft, registration EC-OBK, manufactured by Goodrich, was there any evidence of broken bolts.
- What was found in all incidents was that there had been a loss of tightening torque on the remaining parts.
With respect to loss of tightening torque, Safran Landing Systems explained that it could be due to: improper or unappropriated tightening of the nut or improper part tightened during the last overhaul or improper breakaway torque of the nut to maintain tightness. Safran Landing Systems concluded that this was the most likely cause based primarily on the following findings:
- On the remaining torque bars, on their contact surface with the bolt head, and under the bolt heads, they detected circular friction marks. According to Safran Landing Systems, these circular marks could have been induced by a rotation of the bolt. During overhaul, if the tightening torque is incorrectly applied on the bolt head rather than the nuts, the assembly may rotate causing such marks.
- Two matting areas were also noted along the bolt shank. In Safran Landing SystemsÂ’ experience, a pretension force lose on the bolts14 could lead to lateral movements between the different parts that ensure the tightening and, consequently, damage them during braking.
The last overhaul of the wheel was carried out by SR Technics. During the investigation they indicated that the tightening torque was applied on the nut. They added that as this is located in an area that is difficult to access, they use a tool which, they said, allows them to give the correct tightening torque to the nut.
SEMASA, although it had only carried out several tyre changes on the wheel which did not require removal of the torque bars, in order to ensure that its mechanics gave the correct tightening torque, distributed an internal note reminding them that the tightening torque should be applied on the nut and not on the bolt head.
Although it is not excluded that improper or unappropriated tightening was applied on the nut or that it was applied on the bolt head rather than the nut, the possibility of a loss of tightening torque over time was also raised during the investigation, even if the correct tightening torque had been applied at the last overhaul. Neither Safran Landing Systems, the manufacturer of the wheel, nor the maintenance organizations had any data on this as it was not necessary to measure it during tyre changes.
A subsequent inspection revealed 3 torque bars were missing, one was found in Palma Mallorca, the third is still missing.
On Oct 16th 2025 Spain's CIAIAC released their final report concluding the probable cause of the incident was:
The most likely cause of the incident is considered to be the loss of tightening torque on the No. 2 wheel torque bar fastenings, which caused the torque bar to come loose. However, during the investigation it could not be determined what caused this loss of tightening torque as it could have been due to improper or unappropriated tightening and/or improper breakaway torque of the nut to hold the tightening torque.
The CIAIAC analysed:
With the help of Safran Landing Systems, the manufacturer of the wheel, an analysis has been made of what could have caused the loss of the three torque bars on wheel No. 2. This could have been due to either a rupture of the bolts or a loss of tightening torque.
With regard to the rupture of the bolts, the CIAIAC rules out that this caused the loss of the torque bars for two reasons:
- Neither in the incident under investigation nor in the two subsequent incidents on 19 May and 8 June on wheel No. 3 of the Boeing 737 aircraft, registration EC-OBK, manufactured by Goodrich, was there any evidence of broken bolts.
- What was found in all incidents was that there had been a loss of tightening torque on the remaining parts.
With respect to loss of tightening torque, Safran Landing Systems explained that it could be due to: improper or unappropriated tightening of the nut or improper part tightened during the last overhaul or improper breakaway torque of the nut to maintain tightness. Safran Landing Systems concluded that this was the most likely cause based primarily on the following findings:
- On the remaining torque bars, on their contact surface with the bolt head, and under the bolt heads, they detected circular friction marks. According to Safran Landing Systems, these circular marks could have been induced by a rotation of the bolt. During overhaul, if the tightening torque is incorrectly applied on the bolt head rather than the nuts, the assembly may rotate causing such marks.
- Two matting areas were also noted along the bolt shank. In Safran Landing SystemsÂ’ experience, a pretension force lose on the bolts14 could lead to lateral movements between the different parts that ensure the tightening and, consequently, damage them during braking.
The last overhaul of the wheel was carried out by SR Technics. During the investigation they indicated that the tightening torque was applied on the nut. They added that as this is located in an area that is difficult to access, they use a tool which, they said, allows them to give the correct tightening torque to the nut.
SEMASA, although it had only carried out several tyre changes on the wheel which did not require removal of the torque bars, in order to ensure that its mechanics gave the correct tightening torque, distributed an internal note reminding them that the tightening torque should be applied on the nut and not on the bolt head.
Although it is not excluded that improper or unappropriated tightening was applied on the nut or that it was applied on the bolt head rather than the nut, the possibility of a loss of tightening torque over time was also raised during the investigation, even if the correct tightening torque had been applied at the last overhaul. Neither Safran Landing Systems, the manufacturer of the wheel, nor the maintenance organizations had any data on this as it was not necessary to measure it during tyre changes.
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