Aircraft Flex Hoses


Hoses.  Time to talk about some boring-ass stuff that can kill you.


Hoses in an aircraft are broadly two types:


1) flexible

2) rigid metal


Most people focus on the flex (eg Aeroquip) hoses which are often made of cotton and

rubber and are used for fuel, oil and hydraulic fluid.


The lawyers tell you to change them every 5 years, but they are very expensive and 99%

of people don't.  There is no regulatory requirement to, and since they're legal they must

be safe, right?


Depending upon how many hours are flown and how much heat they are exposed to, you

can probably take a flex hose out to 10 years if it leads a gentle life.


A couple months ago, I changed the left magneto on a tube & fabric taildragger (not mine)

and I had to move the oil cooler out of the way.


The flex hoses from the engine to the cooler were dated 1973 on the metal tags, and they

were hard as a rock.  No legal requirement to ever change them, but suicide not to.


A friend of mine, Gary Ward, used those shitty NASCAR lightweight hoses on his

homebuilt MX2 and across the Gulf of Mexico, he lost 10 quarts of engine oil when one

of them sprung a leak.  Raymond thought he had his smoke on.


Freddy Cabanas had an oil flex hose spring a leak in an S-2C, which wasn't very old at all. 


I've seen plenty of fuel flex hoses in biplanes dry up and completely fail, and pee 100LL

all over the floor, at quite a rate.  Gets your attention.


Seriously consider, when ordering new flex hoses, to specify "firesleeve" which is this

Protective orange outer sleeve - think of a kevlar condom - which protects the delicate

cotton and rubber flex hose, especially in presence of heat (e.g. near exhaust pipes). 

See TSO-C53a and TSO-C75 for more detail.


Another option, instead of the black cotton/rubber flex hoses, is to get the teflon/stainless

steel flex hose (Aeroquip 666), which is tougher and lasts longer.  They have worked

very well for me.


A few years back, an antique twin I flew sprung a fuel leak on the right engine.  Popped

the cowl, it wasn't a flex hose!  Over the decades, a clamp mount on a rigid metal fuel

hose had worn through it.


Easy enough and quick to fix.  But it could have gone very badly in flight.


I spend as much time wrenching as I do flying, so I probably have a different perspective

than most pilots on this, but ... learn your systems!


What you don't know, can sure as hell kill you.



Jan 2016