Note: This question appears to have multiple correct answers in its current format. Whilst it is quite common to have to choose the "most correct" answer in many questions, that is a very difficult choice to make on this question, due partly to the lack of information in the question. We have currently chosen the answer that makes a bit more sense on its own from the other options, but this question and the wording has not yet been verified, so we cannot be sure of the wording, or the correct option. Please put any further exam feedback in the comments or email it to [email protected], thank you!

Learning Objective 021.01.03.01.02: Describe the operating environments where the risk of corrosion is increased and how to minimise the effects of the environmental factors.

Corrosion happens for many reasons. It is primarily a chemical process, where metals which are unstable in nature are turned into more stable states, such as metal oxides, carbonates, etc.

It can happen due to oxidation, where the metal and the oxygen in the air react together to form an oxide. It can also happen due to the presence of moisture, either liquid or as vapour in the atmosphere, and the impurities in the water cause a chemical change in the metal on the surface, which is corrosion. Other types of corrosion can be due to dissimilar metals being in contact with each other, electrolytic corrosion, stress corrosion, amongst others. Corrosion usually breeds corrosion, and one type will often lead to other types occurring in the same piece of material, so an airframe must be checked for it regularly, and measures put in place to stop it occurring in the first place.

Measures to avoid corrosion do depend on the aircraft's expected flying.

• If the aircraft is to fly at low levels near the ocean for long times, then the extremely salty water in the air will cause that kind of corrosion very easily, so the aircraft should be washed often, to provide clean water to the surface, and remove the impurities.
• Aircraft should be stored indoors as much as possible, in hangars, to avoid rain and other weather conditions that will allow for impurities.
• A dry climate will help an aircraft from becoming corroded.
• Any areas without paint, such as chipped or flaky paint areas should be kept painted, as this will provide an extra layer of corrosion protection for the metal underneath.
• The type of material used also massively affects corrosion resistance, whilst aluminium and magnesium are very prone to corrosion, titanium and some cheaper alloys are much better at withstanding its effects. Plastics and composite materials are outright the best though, as their corrosion resistance is unparalleled by metal due to their natural properties.

As mentioned above, we can't be sure of the correct answer, so require your feedback to confirm what the examiner is saying it is. We have had to choose between the options using very fine margins, but here is our thought process.

As washing the aircraft is particularly useful in corrosive conditions, but not in dry climates, we will discount that. A heated hangar is not particularly required, as a cold hangar will also be okay, aircraft are built to fly in very cold conditions (again, it would help, but maybe not the most). Painting the deteriorated parts could help a bit, but also it could potentially hide some of the further corrosion, so we will discount that answer also. That leaves us with replacing the parts with composited and plastics, which would absolutely help the most (but could be super expensive and potentially not viable in all cases).