Sunday, June 24, 2012

Installing Aircraft Hose - The 10 Rules

Hose chafe damage hidden inside firesleeve

  1. Minimize fluid connectionsEach connection is another potential point of failure. The fewer hoses the better.
  2. Each hose shall have a bend. The bend should be in the plane of movement. Hoses should never travel straight from connection to connection. If the hose moves in the horizontal plane then the bend should be in the horizontal plane. When the bend is in a different plane than the movement then there is a twisting force on the hose. This twisting force may untwist the fitting connection, kink, or fatigue break the hose. (ref: Loss of Fokker 27-50 YL-BAW Flight BT-443 May 2006).
  3. Electrical wires should not be attached to flammable fluid carrying hoses.
  4. Hoses should not touch other objects in a way that they might rub and chafe. Outside steel braid hose "hack-saw hose" can cut through steel and aluminum.
  5. Hoses should not pull or tug at the fitting they are attached to. Hose should not be forced into position to get the "B" nut to thread. Do not use the attachment fitting as a bracket to hold the hose in position. If you think you need a "steel" fitting rather than aluminum because it's stronger; ask yourself why does the fitting need to be stronger? 
  6. Hydraulic hoses should have a pressure rating + safety factor greater than the IMPULSE pressure. Hydraulic impulses can be many times the "operating pressure".
  7. Flammable fluid carrying lines in the engine compartment shall be firesleeved.
  8. Inspect hoses for chafing with your hands. The chafe point is not visible since it is against the chafee.
  9. Hoses shall  not touch exhaust components. 
  10.  Oil lines in the engine compartment that travel next to or along exhaust components shall be firesleeved. Protects the hose in case of exhaust system crack or failure.
An old hose can look good on the outside -- this hose passed many visual inspections!

Special Rules:
1. Design fuselage hoses for crash damage.

"Each fuel line within the fuselage be designed and installed to allow a reasonable degree of 
deformation and stretching without leakage. The idea is that the fuselage can be damaged with partial separation or other structural damage without the fuel lines or electrical power cables breaking apart.  Allowing for a certain amount of stretching will help to minimize the probability of a fuel-fed fire inside  the fuselage. As it is used in this requirement, a 'reasonable degree of deformation and stretching'  should be about 10% of the length of the electrical cable."
European Aviation Safety Agency Certification Specifications  for  Large Aeroplanes CS-25 Amendment 10 23 December 2010  

An interesting rule to leave some slack so that in the case of an accident when the structure bends and deforms that the fuel line going to the tank has enough stretch and give so that the hose doesn't rip out of the fuel tank.

1 comment:

  1. Thanks for these great instructions. I am trying to install my own aviation hose and I appreciate this post. Thanks.