There is a number of filters on a typical aircraft, around the vacuum system, and the engine air intake.
Assuming the “air inlet” side of these is visible (it isn’t always) is there any risk in not changing that filter?
For example this one is visible
but this one isn’t (unless you used a borescope)
Yes, filter media can break down causing damage down the line and even engine stoppage.
It’s like the rubber hose replacement on Rotax engines. Looks pretty unnecessary, until it suddenly isn’t.
Buried in the STC for Brackett foam engine air filters is the requirement to change the element annually regardless of condition, and cleaning and reoiling is likewise prohibited. Many people ignore the annual replacement internal for a plane that is e.g. in storage, and I’ve been known to do so on occasion. Long experience with accessory foam filters on motorcycles indicates they last about a decade before the foam starts to break down. On those you typically clean and reoil them with filter oil many times before replacement.
I can’t see any reason to change an open paper vacuum system filter unless it needs it by visual inspection. After a number of years, sure, but again I think the number is about 10 years. Similar to a paper air filter on a car, except that the filter is in less severe service.
The cost of the filter is insignificant compared to the Labour cost of removing the filter and properly inspecting it…………. Just change it ! If the cost of a vac filter is an issue you probably should not be flying.
The labor cost in Peter’s case is undoubtedly zero and point is not whether one can afford to replace a filter, obviously anybody can, but rather whether it is necessary or prudent. And whether any value is gained for the cost of replacing a visually serviceable filter on a scheduled periodic basis.
I would not leave the foam filter on the engine air intake for years. It will eventually disintegrate and bits will get sucked into the engine.
What wondered whether the vacuum system filters really need changing. They are very cheap but occassionally when one orders them they don’t arrive on time and the filter change has to wait until the next service. Usually they can be done at the next 50hr check but one of the vac system filters is a bit harder to get to and when it comes out it is always absolutely spotless.
The maintenance schedule for a lot of our aircraft was written many years ago, when smoking in aircraft was very common, if not quite mandatory. So the cabin filters, usually vac and vac relief, nowadays have a much easier time(assuming you don’t smoke), so possibly a reason to extend their life somewhat?
Doesn’t seem too far fetched:
This is the first reasoned argument for increasing vac filter life, the photo above is more or less what I would have expected of a cabin outflow valve back in the late 1970’s when I started in the airline maintenance business.
