What lines NOT fire sleeved FWF

Was wondering what oil and fuel lines FWF do NOT need to be fire sleeved? I would guess the ones that might not need to be fire sleeved are fuel and oil sending lines (restricted AN fittings from engine to units), manifold pressure line, fuel drain lines (from mech fuel pump & sniffle valve), prop governor oil line, oil seperator/breather line, and the four cylinder/piston oil drain lines.

It might have been easier to ask which ones need to be fire sleeved: oil cooler lines, fuel lines from firewall to mechanical fuel pump to fuel servo to flow divider.

Are there any others that need to be or not need to be -- pros and cons? Thanks. Dave

While there is no regulatory requirement for us to comply with FAR 23 (design standards for type certificated light aircraft), it does provide a useful benchmark. FAR 23.1183 requires each line carrying flammable fluids ahead of the firewall to be at least fire resistant (i.e. covered in fire sleeve), except for "vent and drain lines, and their fittings, whose failure will not result in, or add to, a fire hazard".

My interpretation of FAR 23.1183 is that lines going to fuel and oil pressure senders should be fire sleeved, but that drain lines from fuel pump, sniffle valve, etc do not. This makes sense as normally the drain lines would not have flammable fluid in them, but fuel and oil pressure lines would have fluid that could make a fire worse if they were to fail.

It is also interesting to read that FAR 23.1162 states "components, lines, and fittings ... located behind the engine-compartment firewall must be constructed of such materials and located at such distances from the firewall that they will not suffer damage sufficient to endanger the airplane if a portion of the engine side of the firewall is subjected to a flame temperature of not less than 2000 ?F for 15 minutes." FAA Advisory Circular 20-135 Powerplant Installation and Propulsion System Component Fire Protection Test Methods, Standards and Criteria expands on this by stating "use of aluminum alloy for any size line/fitting on either side of a firewall should be avoided". My aircraft doesn't meet this criteria, as I have an aluminum fuel line in the cockpit connecting to an aluminum fitting at the firewall. But I can see how a fire on the engine side of the firewall could cause this aluminum fitting or line to melt and thus make things even worse. If I were doing this again, knowing what I know now, I would probably use a steel fitting at the firewall, and perhaps a flexible hose with steel fittings connecting to it on the cockpit side.

Note that none of above are requirements for our aircraft. But, they do provide a useful benchmark as to best practices. The odds are hopefully very small that we will ever find ourselves in a situation where this would make a difference. But, against all odds, back in March, I found myself in a car that caught fire after an accident. My wife and I were lucky to escape the fire, but I would have preferred the car to be more fire resistant. If my aircraft ever develops a fire ahead of the firewall, I hope the fire will remain as small as possible until after I can get it on the ground and get out of the aircraft.

Kevin Horton said:

It is also interesting to read that FAR 23.1162 states "components, lines, and fittings ... located behind the engine-compartment firewall must be constructed of such materials and located at such distances from the firewall that they will not suffer damage sufficient to endanger the airplane if a portion of the engine side of the firewall is subjected to a flame temperature of not less than 2000 ?F for 15 minutes."

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Plastic brake fluid lines full of MIL-H-5606 are a pretty good example given the above conditions. An object located 6" behind a plain stainless firewall reaches 400F in less than 30 seconds. MIL-H-5606 has a flash point around 250F.

my fwf kit

Assuming Van's and Aerosport are good examples:

Fire sleeved:
- fuel line to the engine pump
- fuel line to the fi servo
- fuel line to the spider

Not firesleeved.
- all oil lines were braided steel, not sleeved
- fuel line to the fuel pressure sender, braided steel
- fuel lines from the spider, which are only inside the baffling, steel tube
- prop governor oil line, steel tube

Excellent points

Thanks for the replies from both Hortons (& Don). I agree Kevin. Just because something is not "required," doesn't mean it shouldn't be done. There are numerous instances where things happen forward of the firewall that are unplanned or just happen. An example is an aluminum AN oil fitting that breaks off and the oil escapes, so you become a glider. I know someone that has happened to. That is why I have all steel fitting for the oil and fuel lines FWF(I actually have an aluminum restricted flow fitting for the fuel sending unit because I couldn't find a steel one). Probably overkill and extra weight, but I'm okay with that.

Excellent point on not having an aluminum line for the fuel line from the electric boost pump inside the cockpit side to the FW bulkhead fitting.

I wonder what would be the best way to deal with the brake fluid? The reservoir is aluminum and would melt relatively quickly. I need as much leg room as I can get so I don't want to use the brake cylinder reservoirs. Has anybody made a change to this using the same "setup" as Van's? Not excited about a steel reservoir either?

db8 said:

. I need as much leg room as I can get so I don't want to use the brake cylinder reservoirs.....

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Are you sure this would be a problem for you? Have you sat in your cockpit with the upholstered seats installed? I am 5'10" and with cockpit adjustable rudder pedals, STILL require the pedals to be locked into the most aftward position for maximum comfort. When sliding the pedals all the way forward to the firewall, my feet can barely reach them and even then there is no conflict with the brake cylinder reservoirs I installed to replace the kit supplied (firewall mounted) reservoir. The other day, I had a pilot who is 6' tall "try out" sitting in the RV-8 cockpit and he too preferred the rudder pedal locked in the full aft position.

Have you looked at a new Skyhawk or other part 23 airplane lately without the cowl? I was looking at the FWF of a 2004 C-172SP this weekend. You may be surprised to see how many hoses are not firesleeved. It would seem to me based on what I saw that Cessna does not interpret FAR 23.1183 to mean firesleeved hoses.

Of course, Cessna is not our metric for excellence.

For what it's worth, I used Van's FWF hoses (well, most of them) which is exactly as Don listed above.

Rick6a said:

Are you sure this would be a problem for you? Have you sat in your cockpit with the upholstered seats installed? I am 5'10" and with cockpit adjustable rudder pedals, STILL require the pedals to be locked into the most aftward position for maximum comfort. When sliding the pedals all the way forward to the firewall, my feet can barely reach them and even then there is no conflict with the brake cylinder reservoirs I installed to replace the kit supplied (firewall mounted) reservoir. The other day, I had a pilot who is 6' tall "try out" sitting in the RV-8 cockpit and he too preferred the rudder pedal locked in the full aft position.

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I agre with Rick on this - I knwo that some folks have very long legs, and brake reservoir interference is possible, but my legs woudl have to be 6 inches longer for it to be a problem. I am beginning to thin kthat cushions should be an early purchase for an RV builder - at least before they start cuttign sticks, placing pedals, installing seat-back hinge points, etc.

Couple comments.

<<Not firesleeved.
- all oil lines were braided steel, not sleeved
- fuel line to the fuel pressure sender, braided steel>>

The mere presence of steel braid outer sheath isn't likely to add significant fire resistance, at least not if your interest is keeping the fluid inside. The hose core is either rubber or teflon. I think the steel braid will glow red and the core will melt (as usual, the really curious are welcome to send samples for the burn rig). Personally I'd firesleeve any hose subject to internal pressure.

<<new Skyhawk or other part 23 airplane....You may be surprised to see how many hoses are not firesleeved.>>

I've not looked at any late model certified airplane, so I have no idea what they're using...but perhaps it is integral firesleeve hose, usually a brown or blue sheath?

<<Excellent point on not having an aluminum line for the fuel line from the electric boost pump inside the cockpit side to the FW bulkhead fitting.>>

Now I'm curious. I'll round up a steel -6 bulkhead fitting and install it with an aluminum line and nut on a mock firewall. We'll find out how hot it gets.

<<I wonder what would be the best way to deal with the brake fluid? The reservoir is aluminum and would melt relatively quickly.>>

The standard reservoir is on the engine side of the firewall. Melting it and dumping the brake fluid on the engine side is not a good thing; obviously it will feed the fire. However, at least said fire is on the engine side, not in the cockpit. Very different from a melted plastic brake line on the cockpit side of the firewall, which could easily result in open flame at your feet.

If you really wish to ensure a no-melt brake fluid reservoir, surround it with a small steel box closed on the bottom and three sides, top open. Very easy to do.

Can't prove it at this time, but consider a theory. Like real estate, location makes a difference. I think an engine compartment fire follows the airflow. Initially, the hottest part of the firewall should be the lower center area surrounding the cowl exit. Components located in this area, on the engine side or the cockpit side, should get careful attention. I suspect components located at the firewall perimeter as well as those located high on the firewall are not as critical, at least if you get the fire damped in a minute or two (prop stopped to end oil pumping, fuel supply closed).

Long legs

Yes, I have set everything up with the seat cushion, back cushion (even moved back slightly from plans), stick, instrument panel and pedals, and I wish there was more room. I purchased the seperate brake reservoirs, put them on the brakes, and it seemed to me it could interfere with the firewall with them all the way back. So, I switched to the old system (a lot easier to mess with the brake fluid anyway). My inseam is 36" and I would be very surprised if many long legged people have not had issues with the rudder pedals being short when all the way back.

Dan, do you thing the stainless steel box for the brake res. would work to use the .018 SS that is used for the firwall? How about the lines at the T where they branch off and make their run to the brake cylinders (on the cockpit side)? Maybe they would be ok if they were protected by the box and no major worries of changing that? Dave

<<Dan, do you thing the stainless steel box for the brake res. would work to use the .018 SS that is used for the firewall?>>

Doesn't have to be stainless. Any light gauge (0.018 to 0.025") mild steel sheet would be fine; just paint it.

<<How about the lines at the T where they branch off and make their run to the brake cylinders (on the cockpit side)? Maybe they would be ok if they were protected by the box and no major worries of changing that?>>

Obviously a plastic tee is poor. Brass fittings have a higher melt point (about 1700F) than an aluminum fitting (about 1100F), so you have a lot of plumbing options. A filet of intumescent silicone sealer around the penetration on both sides of the firewall (3M Fire Barrier 2000 or similar) is a fine idea.

DanH said:

Now I'm curious. I'll round up a steel -6 bulkhead fitting and install it with an aluminum line and nut on a mock firewall. We'll find out how hot it gets.

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Hello Dan,
Did you ever do this specific experiment? I have a -6 SS bulkhead fitting through the firewall with aluminum fuel line (and nut) on the cool side of the firewall.

Andrew Anunson said:

Hello Dan,
Did you ever do this specific experiment? I have a -6 SS bulkhead fitting through the firewall with aluminum fuel line (and nut) on the cool side of the firewall.

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Not specifically an aluminum line connected to a steel bulkhead fitting. I did do enough burns with steel fittings to know the cabin side can glow red when the front side was subjected to FAA standard 2000F, just like the stainless sheet in which they were installed. So, my own has a -6 stainless steel flared line between the steel bulkhead fitting and the boost pump, with an S-bend for strain relief.

Dan,
400 degrees 6" aft of firewall in seconds? Fire sleeved shoes and pants? If the heat follows the airflow, then the front floor seems in need of protection as well as what has been mentioned.

Fire Resistant Hydraulic Fluid.

ROYCO 782 MIL-PRF-83282D
Flash point is 205 Deg C. = 401 Deg F.
Fire point is 245 Deg C. = 473 Deg F.
?As a result a synthetic hydrocarbon-based fluid, MIL-H-83282 was developed. This fluid is completely compatible with MIL-H-5606 fluids and MIL-H-5606 hydraulic system materials?.
The Military switched over to Fire Resistant Hydraulic Fluid many years ago.