Oxygen, heaters, pressurization

Six procedures. The first three are oxygen work and they have their own discipline.

Procedure 0 — Oxygen cleanliness (R1, R4)

Before touching any oxygen component.

1. Clean hands. No lotion, no sunscreen, no oil.
2. Oxygen-clean tools and equipment only, kept separate and marked.
3. No smoking, no ignition sources, no powered aircraft in the area.
4. Correct materials only — seals, lubricants and tape approved for oxygen service.
5. Confirm cylinders are within hydrostatic test date.

Check — name the last thing your hands touched. If it was a lubricant, a solvent-soaked rag or a sandwich, wash them (AF-G Concepts §2).

Procedure 1 — Purge an oxygen system (S2)

1. Procedure 0.
2. Follow the manual's purge procedure — typically flowing dry, oil-free oxygen or nitrogen through the system to remove moisture and contaminants.
3. Purge at the specified rate for the specified time. Rate matters: rapid flow heats the gas.
4. Confirm completion per the procedure.

Check — purging is specified because moisture in an oxygen system freezes at altitude and blocks it. If you are not following a written procedure with a rate and a duration, you are not purging.

Procedure 2 — Service an oxygen system (S3)

1. Procedure 0.
2. Confirm the correct gas — aviator's breathing oxygen, not medical, not welding. The specification differs in moisture content, and moisture is what freezes.
3. Connect per the manual, bonded.
4. Charge slowly. Rapid charging heats the gas by compression, which is both a fire risk and a cause of over-reading pressure.
5. Charge to the pressure specified for the ambient temperature — cylinder pressure varies with temperature, and a cylinder filled hot is undercharged when cool.
6. Leak check with an approved leak-detection method — not soap containing hydrocarbons.
7. Record the servicing.

Check — charge slowly, and check pressure again when it has cooled. A cylinder that reads correct while warm will read low an hour later.

Failure — using the wrong gas grade, or charging fast. Both are invisible at the time.

Procedure 3 — Inspect oxygen components (S1, S4, S5, S6, S7)

Cylinders (S6): hydrostatic test date, external corrosion, dents, gouges, security of mounting, valve condition, and any evidence of overheating.

Regulators (S5): security, correct pressure output, leakage, condition of gauges.

Masks and hoses (S4): cleanliness, hardening or cracking of hose, condition of the mask, security of connections, and cleaning only with approved materials — many common cleaners leave a hydrocarbon residue.

Chemical generators (S7): safety pin fitted, no evidence of initiation or heat, within life, correctly secured, and handled with the pin in place at all times.

Check — the hydrostatic date is a hard limit. A cylinder out of date is unairworthy regardless of condition, and it is one of the time-based items no inspection can substitute for (AF-B Concepts §3).

Procedure 4 — Inspect an exhaust heat exchanger for cracks (S13)

Read AF-G Concepts §3 first. This is a carbon monoxide inspection.

1. Remove the shroud so the exhaust component inside is accessible.
2. Clean the surface so cracks are visible.
3. Inspect welds, slip joints, and areas of stress concentration, with light and magnification (GEN-K Procedures Procedure 2).
4. Where the manual requires, perform a pressure leak check of the exhaust system (PP-L).
5. Inspect the shroud itself and its sealing.
6. Any crack in an exhaust component within a heat shroud is a rejection. It is not a repairable-in-service item unless the manual explicitly says so.

Check — a visual inspection of the outside of a muffler proves very little. If the manual offers a pressure check, that is the inspection; visual is the screen.

Procedure 5 — Clean and inspect a pressurization outflow valve (S14)

1. Depressurize and de-energize, and confirm.
2. Remove per the manual, noting orientation and any rigging.
3. Clean with approved materials; the valve is often fouled by cabin dust and contamination, and that is what makes it stick.
4. Inspect seat and seal condition, diaphragm condition, filter or screen, and free movement through full travel.
5. Reinstall, rig per the manual, and functionally check.

Check — check free movement through full travel by hand before reinstalling. A valve that sticks anywhere in its range produces intermittent pressurization faults that are attributed to the supply (AF-G Concepts §4).

Procedure 6 — Inspect a combustion heater and its fuel system (S10, R6)

1. Inspect the fuel supply lines and connections for leaks — a fuel leak at a combustion heater is a fire in the airframe.
2. Check the combustion air and ventilating air paths are clear and separate.
3. Check overheat switches and safety devices — these are the protections and they are tested, not assumed.
4. Inspect the combustion chamber per the manual for cracks, which would put combustion products into the ventilating air — the same hazard as S13.
5. Check drains clear.

Check — the overheat protection must be tested, not inspected. It is the device that stops a heater fire, and a switch that looks fine and does not function is worse than none.

The checks, collected

License

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