5 Year Hose Change

[sandpiper]

I am just finishing my 5 year hose change and want to share a couple of problems found that, if not corrected with new hose, could have led to serious problems;

 

1. The oil hose that runs from the bottom of the engine to the oil tank was routed (from the factory) such that it was against the firewall prior to entering the tank. About 2 inches up the firesleeve from the tank attachment I noticed a hole worn in the firesleeve. When removing the firesleeve I found that the hole was also worn into the oil hose itself. At the point of contact with the firewall is a very small bolt head which was the culprit. I rerouted the hose which not only solved the problem but also shortened the hose. The original installation was very tight up against the firewall and none of this was visible without removing the hose. Since I run 95% mogas the tank has never been removed for cleaning until now. Even though the tank was perfectly clean as expected, hindsight indicates this was poor practice. Total time is 311 hours.

 

2. The water hose from the top rear left cylinder is one of many running to the little tank on top of the engine. Unlike most of the other hoses that accomplish this in a pretty straightforward manner, this hose makes about a 150 degree reversal to enter the tank. It is one of two hoses with an internal spring facilitating a turn. There is also a piece of firesleeve on the outside of the bend held in place with plastic ties. Once the hose was off, I straightened it and noticed a hole worn about halfway through the hose on the inside of the bend. This was not visible when the hose was on the engine and was only visible when the hose was straightened and forced to lay flat. At first I thought it was from one of the plastic ties being too tight but I don't see any other marks from that tie on the hose. Also, since this is inside a crease in the hose caused by the bend (making it invisible until straightened), the plastic tie would have been held in that crease which was not the case. Again, this was a factory installation.

 

Anyhow, the hose change turned out to be a usefull exercise, at least in my case.

[Roger Lee]

Hi John,

 

Thank you, thank you, thank you.

 

This has been the very point I have been trying to make. You can't see these during inspections, looking at a hose or squeezing it is useless, it can have hidden issues inside. No one has X-ray eyes to see under fire sleeve. So a line has to be drawn in the sand somewhere and from 20+ years of experience Rotax picked 5 years as a place to try and save some from a bad experience. Don't fix it unless it's broke isn't good and may be a poor maint. Practice.

We just can't see everything, under everything, in fire sleeve, ect... So at some point every thing needs to be dis-assembled to be checked and with all the issues I have seen after 30 + hose changes, I'll do mine at 5 years every time. The factory doesn't always do it right, just as I found out a few weeks ago on a CTSW.

 

The re-routing of that bottom fuel hose like the picture that was posted in the maint. Section could help with chaffing and a reduced radius hose issue that you may not even know you have. Pulling all those hoses to inspect and fully authorize the plane to be in a safe condition for flight after you have been warned by the authorized engine MFG and looking for chaffing, cracking, kinks, reduced radius or any other hidden signs of failure, hec you might as well replace it and not worry for the next 5 years. Even if you visually and don't find anything wrong that won't stop an older hose from having a catastrophic failure that no one can predict. Sure new hose can have a failure, but less likely than an old hose especially if it has some hard bends in it and has been through lots of heating, cooling and pressure cycles. Requirements and playing it smart could add up to two different things.

 

 

Be pro-active Not re-active, it's usually less expensive and painful at times.

 

 

As we say on the fire department.

"This is no honor in putting out a fire that could have been prevented"

 

 

 

Hence;

There is no honor in fixing something that could have been prevented.

 

You can see after 30 years of helping people and fixing their problems I would rather be pro-active and preventative in my approach to problems. Most of them said, Well that never happen like that before. Wish I had a nickel for every time I heard that.

[Doug Hereford]

Roger/Sandpiper,

Since I am one of the ones who has been vocal on the hose change requirement, I will speak up again:

 

I have stated before, that I believe as a general rule, changing fluid carrying hoses, especially flammable liquid hoses, around a five year mark is usually a good idea.

 

Where I disagree with the general consensus, is that NOT changing the hoses exactly at or before the five year point, puts the aircraft (SLSA) out of airworthiness. There is simply no regulatory basis for this opinion.

 

In sandpiper’s example above, as in each and every example I have heard, the discrepancies related to hoses, were due to improper routing, and/or support and possibly poor prior inspection performance. I believe, that if as much effort were placed on proper inspection, and installation of hoses as has been placed on arguing for arbitrary replacement, fewer problems would be found.

 

Aircraft hoses have been around since the Wright Brothers, and their idiosyncrasies pre-date Rotax, and SLSA by just as much. I will say it again: If there is truly an unsafe condition out there due to hose age, then the relevant SLSA manufacturer MUST issue a Safety Directive to legally mandate changing the hose. Otherwise, maintenance providers should perform quality Condition inspections, and advise owners to base their decision to change hoses on the summary of all factors (age, time-in-service, type of hose, and operation involved).

 

Doug Hereford

[Doug G.]

There is also no honor in fixing things that are not broken - especially if you charge for it. Many auto repair places have ended up in court for doing that. As an example: if my engine reaches TBO but the compression is good, the oil shows no sign of inordinant wear, the mag plug shows no negative indications, and all other indicators are good, I am not going to have my engine overhauled or replaced. If it ain't broke, and it is not reasonably preventative, don't fix it.

 

I think the hose thing is frustrating because Rotax has not given its reasoning based on any empirical (or even anecdotal) data. For all we know the MTBF on the hoses may 15 or 20 years. All Rotax is saying is, "trust us."

 

Having said that - I would change the hoses based on the lack of information, even thought Rotax cannot mandate this except by SD or ASD...unless I could figure out a way to reliably test the hoses.

[C ICEY]

my only forced landing came 2.4hrs after the wrench.

[Jim]

Speaking of the hose change, next time you have the cowl off, you might want to check for metal-to-metal contact between the coolant cap and the aluminum carb balance tube. I had to get things moved around.

[Farmer]

My only forced landing came less than thirty minutes run time after annual. Twenty five minutes of run up and check out, and about four minutes in the air. Yes I did make it back inside the fence, barely. Honolulu International is kind of busy place to just turn around and return. No paperwork on that one.

[S3flyer]

We've certainly danced around this topic many times and, at least to me, the 5 year rubber replacement service is only recommended, and not required. An S-LSA manufacturer could make it mandatorty with the appropriate bulletin, though. I mentioned in a prior thread that Rotax was not the only engine manufacturer that recommends replacement -- Lycoming has the same recommendation. It is also not mandatory, other than for specific fuel lines. Lycoming Maintenance Manual excerpt:

 

As airplanes and engines attain age, there appears to be a need to reemphasize the inspection or replacement of engine hoses or lines carrying fuel, oil or hydraulic fluid. The hose manufacturers definitely recommend regular inspection and replacement of all such hoses at engine overhaul even though they look good. Age limit of rubber-steel or fiber-banded hose has generally been established at four years. This limit of four years is generally considered to be “shelf” life.

 

..........

 

Lycoming Service Bulletin No. 509 must also be complied with if rubber hose is used to carry low-lead aviation gasoline. Aeroquip, the manufacturer of hose used by Lycoming, has recorded several failures of 601-type rubber hose. Although it is satisfactory for other purposes, this hose appears to be adversely affected by low-lead aviation gasoline. 601-type rubber hose used for low-lead aviation gasoline is to be replaced after no more than two years of use. Aeroquip and Lycoming recommend that rubber hose be replaced with Teflon hose.

 

 

I tend to defer to the collective wisdom of both Rotax and Lycoming (probably Continental as well) and will have my recommended 5 year rubber replacement service done at my next annual.