Central air filter installation

[John B Reed]

Hello, I have had more than my share of installing the central air filter with the bolt from the bottom up, trying to thread it into the top housing. I'm not the only one I am sure who have had this wonderful experience. The other day I saw something in a C172N/S where the housing had the bolt already installed and all you have to do is install the filter and tighten the plastic wing nut. My question is - on other aircraft without this: Can I change out the assy with another assy with the wing nut; Or get a bolt, cut off the head and make a thread both ends and install it into the housing - without any official paperwork?

 

[455 Bravo Uniform]

Is that how it came from the manufacturer?

You could easily purchase all-thread and cut it to proper length, no need to use a bolt, cut, and thread as you proposed.

Legal, don’t know, the smart A&Ps will be along shortly to advise on paperwork.

As to safety, you’d have to consider possible failure modes and see if you introduce a new way to crash-n-burn converting as above.

 

[Gary Ward]

I would say no...

 

[John B Reed]

Is that how it came from the manufacturer?

Yes - I would be changing how it came from the meanufacturer. Perhaps it will be a minor alteration and just require an entry in the maintenance records for the airframe. I don't see any consequence of doing this - the central air filter will be attached securely regardless. You haven't lived until you've replaced one of these filters.

 

[Gary Ward]

Yes - I would be changing how it came from the meanufacturer. Perhaps it will be a minor alteration and just require an entry in the maintenance records for the airframe. I don't see any consequence of doing this - the central air filter will be attached securely regardless. You haven't lived until you've replaced one of these filters.

Been there and have replaced that filter, it was a challenge with the bolt to get started.
Then it was 3 months later I went with G5 and removed my vacuum system with a clean filter.

 

[Magman]

Consider the filter model that has tubing out of each end.

No mount ; just clamped in convenient spot.

This may be OEM on later 150’s & 152’s.

If not; my take is Minor Alteration.

What does it weigh, 4 ounces?

Same for using all- thread to replace the Screw if you go that way.

Either way , replacing the ancient hose is far more important.

 

[Bell206]

Can I change out the assy with another assy with the wing nut; Or get a bolt, cut off the head and make a thread both ends and install it into the housing - without any official paperwork?

If talking about the vacuum system filter assembly, it depends on the setup of your existing system. However, in most cases one filter assembly can be replaced with a different filter assembly. As to the "official paperwork" part of the question it depends what you are referring to. But yes, it will require a logbook entry at a minimum. However, whether you need additional paperwork will depend on your mechanic and how he defines the alteration.

 

[Magman]

I believe the Filter I mentioned is p/n D9-18-1.

IIRC the aircraft I saw these in did not have a mount on the

backside of the Firewall so may be OEM.

My take is there are many tasks on aircraft that are not

easy to do and are often ignored.

Aircraft that do not have a Central Vacuum Filter have filters on the

individual gyros. These should be replaced at 100 Hour interval.

Generally these are the old, large “AN” gyros

and require removal of the unit to do this. Since the individual filter is

small they have little capacity and tend to become obstructed.

What do you think of the chances of them getting done?