Latest revision to maintenance manual

[Hank Biesbroek]

Following the conversation - Interesting!

Just curious, if the revision is dated Oct 2010, why are we just talking about it now?

Was it just released by Cessna, or has it been out since October 2010?

Hank

[Gord Tessier]

I don't get that either. The revision was dated July, but the effective date was last October. I would never have even known about it until next June 15th which is when my annual is and that's when I check to make sure I have the latest revision. I am in Canada and have gotten conflicting information as to whether they are mandatory so I have asked Ottawa directly (Transport Canada Headquarters). A fellow pilot did ask earlier in the year and was told he did NOT have to do them so the answer should be the same. I hope

[sns3guppy]

What do you mean zinc chromate doesn't prevent corrosion?

Exactly what I said.

Chromate is a surface treatment which acts in two ways; it protects the surface to some degree, and in some applications can serve to aid in retaining anticorrosive agents. What you're likely used to seeing as zinc chromate is a surface paint, although some people mistakenly refer to it as a chromate conversion (something entirely different), which is another process that converts the metal surface through a process of chemical change and oxidation.

Chromate conversion is better known as alodine, which is a much better method of treating aluminum surfaces than simply painting with zinc chromate paint (often used as a primer).

If you've had much experience around older airplanes that had zinc chromate (the real stuff; not the green spray paint that's sold today as "zinc chromate), you'd have seen it peeling and ineffective. It's no longer a barrier, it's not providing surface conversion, and it doesn't account for numerous forms of corosion (including those that form under surface coatings, such as filiform corrosion).

Some aircraft that have used surface sealants and treatments experienced increased rates of corrosion . If you've ever worked on Sabreliners, for example, you'd know exactly what I mean. Further, chromates do nothing for electrolytic corrosion in many cases, especially between faying surfaces, in bolt and rivet holes, and between layers, lap joints, etc. Surface paints and chromates don't prevent intergranular corrosion, fretting corrosion and other associated metal weakening and loss; in fact, where mechanical corrosion occurs, it removes the chromate.

Most aluminum comes with a surface of pure aluminum, sometimes referred to as Alclad. The alclad oxidizes, and provides a corrosion barrier to the underlying material.

spraying down the inside parts of your airplane sounds good, but doesn't stop corrosion from happening.

[Ernie Martin]

At the time the SIDs were being developed, it allowed one year from effective day for compliance. If that hasn't changed, make sure the other Canadian pilot didn't have to do them simply because it was not due yet.

Ernie

[Gord Tessier]

Thanks Ernie, Cessna put a date of may 1st, 2012 to comply by. All the guys I talk to in Canada aren't going to do them. I am waiting for a response from our CAIR's people in Ottawa for guidance.