- Objectives
To control the aircraft structural corrosion below Level 1, when the structural corrosion is above Level 1 (that is, with the happening of Level 2 or Level 3 corrosion), it is a must to decide relevant amendment measures according to the evaluation results. For example, adjust or change the aircraft maintenance plan, work procedures, anti-corrosive or anti-rust solution, and methods of cleaning the aircraft structure in order to control the corrosion below Level 1. If no correction is made, it can cause flight safety hazards.
- Definition:
LEVEL 1 Structural corrosion:
Corrosion occurring between successive inspections that is local and can be reworked/blended-out within manufacturers' allowable limits (e.g., SRM, Service Bulletin, etc.). or
Corrosion occurring between successive inspections exceeds allowable limit but is local and can be attributed to an event not typical of operator usage of other aircraft in the same fleet (e.g., Mercury spill).or
Operator experience over several inspections has demonstrated only light corrosion between each scheduled inspection but the latest inspection and cumulative blend-out now exceeds allowable limits.
LEVEL 2 Structural corrosion:
Corrosion occurring between successive inspections that requires a single re-work/blend-out which then exceeds allowable limits, requiring a repair/reinforcement. or
Corrosion occurring between successive inspections that is widespread and requires a single blend-out approaching allowable rework limits.
LEVEL 3 Structural corrosion:
Corrosion found during the first or subsequent inspections, which is determined (normally by the operator) to be an urgent airworthiness concern, requiring expeditious action.
- Applicability
The aircraft structure of all models, including the door structure, aircraft skin, Pylon, vertical stabilizer, horizontal stabilizer and aircraft wings.
- Conclusion
Where Level 3 structural corrosion is found in the aircraft, it is a must to review if the aircrafts of the same model have the same condition to ensure that other aircrafts can timely find similar issues and to control the structural corrosion below Level 1.
Where the said Level 3 structural corrosion is one single issue (such as transporting high-corrosive objects), there is no need to adjust or change the aircraft maintenance plan, work procedures, anti-corrosive or anti-rust solution, and methods of cleaning the aircraft structure.
Summarized by: Lu Cheng-Chieh of NASC
- References
※ FAA AD 90-25-05
※ Boeing 777 MPD
※ Google photo search: Aloha Airlines