📖 The lesson
Part 1 — Lights (ATA 33)
External lights
| Light | Location and colour | Purpose / rules |
|---|---|---|
| Navigation (position) | Red — left wing tip; green — right wing tip; white — tail, facing aft | Show direction of travel; red and green each cover 110° from straight ahead, white covers 140° aft |
| Anti-collision | Red rotating or flashing beacons on top and bottom of the fuselage; high-intensity white strobes on the wing tips and tail | Must give 360° coverage and flash 40–100 times a minute (CS 25.1401). The red beacon is switched on before engines start or the aircraft moves, to warn ground staff |
| Landing | High-intensity white, in the wing roots, fuselage or retractable units under the wings | Illuminate the runway; may be retractable with motors and limit switches; heat and vibration shorten lamp life (LEDs now common) |
| Taxi and runway turn-off | On the nose gear (turning with or fixed to the strut) | Light the taxiway ahead and to the sides; often switched off automatically when the gear retracts |
| Logo | On the tailplane, lighting the fin | Visibility and company identification |
| Wing / ice inspection | On the fuselage, aimed along the wing leading edges and at the engine inlets | Let the crew see ice at night (Chapter 15) |
| Service lights | Wheel wells, cargo holds, service and equipment bays | Maintenance and loading; often switched by door switches |
Internal lights
- Flight deck: integral panel lighting (edge-lit panels and lit legends), flood lights, dome lights, map and chart lights, and white storm lights that are turned up in thunderstorms to reduce dazzle from lightning. Annunciators have a BRIGHT/DIM selector and a lamp test to show every warning and caution light works.
- Cabin: general lighting (fluorescent tubes on older aircraft, LED on newer, often with mood lighting), entry and galley lights, reading lights in the passenger service units, and passenger signs — fasten seat belts, no smoking / no electronic devices, return to seat — controlled from the flight deck and cabin-crew panels.
- Lavatories: lights brightened when the door is locked, plus the "occupied" sign. Cargo holds: lights switched from the loading panel or door.
Emergency lighting
- Components: illuminated exit signs (locator and marking signs at and above each exit — red EXIT lettering or the green "running man" symbol), general cabin emergency lights, floor-proximity escape-path marking (electrical strips or photoluminescent strips that glow after being charged by cabin light), and exterior emergency lights that light the slides, over-wing escape routes and the ground.
- Power: separate emergency batteries (in each light unit or in emergency power supply units), kept charged from the aircraft DC system, so they work after a total electrical failure and even if the fuselage breaks.
- Control: a flight-deck switch with ARMED, ON and OFF (armed for every flight; a warning shows if it is not), and a cabin-crew switch that can turn them on independently. When ARMED they come on automatically on loss of normal DC power.
- Requirement: at least 10 minutes of illumination after an emergency landing (CS 25.812). Batteries are capacity-tested and replaced on schedule; photoluminescent strips must be kept clean and charged.
Part 2 — Oxygen (ATA 35)
Why oxygen is needed
The proportion of oxygen in air is the same at all altitudes (about 21 %), but its partial pressure falls with altitude, so less oxygen reaches the blood: hypoxia. Its onset is insidious — euphoria, poor judgement, loss of colour vision and coordination — and the person rarely notices. After a decompression, the crew must get oxygen before their time of useful consciousness runs out.
- Flight crew must use supplemental oxygen whenever the cabin altitude is above 10 000 ft, and on aircraft operating above FL250 they must have quick-donning masks that can be put on with one hand within 5 seconds (CS 25.1447).
- Passenger oxygen must be presented automatically before the cabin altitude exceeds 15 000 ft — in practice the masks drop at about 14 000 ft — and can be deployed manually from the flight deck. The supply duration is set by the operating rules for the route (for example the time needed to descend to 10 000 ft or below over high terrain).
- First-aid oxygen bottles are carried for passengers who need it for medical reasons; portable walk-around bottles and smoke hoods (PBE) protect the cabin crew.
Oxygen sources
| Source | How it works | Typical use |
|---|---|---|
| Gaseous oxygen | Aviator's breathing oxygen (at least 99.5 % pure and extremely dry, so it cannot freeze in valves) in high-pressure cylinders — steel or composite-wrapped — at about 1 850 psi when full | Flight crew on all types; passengers on some types; portable bottles |
| Chemical generators | A sodium chlorate core with iron powder decomposes when ignited, releasing oxygen for about 12–22 minutes | Passenger masks in PSUs, lavatories and galleys; PBE hoods |
| Liquid oxygen (LOX) | Stored at −183 °C in insulated converters; very compact | Mainly military |
| On-board oxygen generation (OBOGS) | Molecular-sieve beds extract oxygen from bleed air | Military; emerging in civil aircraft |
Crew system: distribution, regulation and masks
- The cylinder has a shut-off valve and a pressure regulator/reducer that lowers the pressure for the distribution lines; a pressure transducer shows cylinder pressure on the flight deck; an over-pressure (thermal) relief vents through an overboard line capped by a green discharge disc on the fuselage skin — a missing disc means the cylinder has vented.
- Quick-donning masks have an inflatable harness, smoke goggles and a mask-mounted diluter-demand regulator: NORMAL (oxygen diluted with cabin air in proportion to altitude, delivered on inhalation), 100 % (pure oxygen on demand) and EMERGENCY (positive pressure, which also keeps smoke and fumes out of the mask and goggles). Above about FL390 positive pressure is needed to keep enough oxygen in the lungs.
- A flow indicator (blinker) in the stowage box shows flow when the mask is tested; crews test masks before flight with the PRESS-TO-TEST control.
Passenger systems
- Continuous-flow drop-out masks stowed in the passenger service units, lavatories, galleys and crew rests. The doors open on a signal from a cabin-altitude pressure switch (or the manual "MASK MAN ON" control).
- Oxygen flows when the passenger pulls the mask towards them: the lanyard fires a chemical generator or opens a valve in a gaseous system. The reservoir bag may not inflate even when oxygen is flowing.
- Gaseous passenger systems use a continuous-flow regulator whose output increases with cabin altitude; chemical systems need no plumbing but a generator, once fired, burns to completion and gets very hot.
Charging, maintenance and safety
Oxygen and oil do not mix
Pure oxygen makes ordinary materials burn violently, and oil or grease can ignite spontaneously in it. Keep oxygen equipment and tools free of oil and grease; use only oxygen-compatible lubricants, thread tapes and leak-detection solutions; no smoking or naked flames; bond/earth the aircraft and the oxygen cart; and never use oxygen to blow out lines, inflate tyres or charge accumulators.
- Charging gaseous systems from an approved oxygen cart through the charging valve, slowly — rapid filling heats the gas by compression and can start a fire — to the pressure given by the AMM's temperature-correction chart.
- Cap every open line and fitting; leak-test with oxygen-safe solution; replace cylinders at hydrostatic test due dates.
- Chemical generators are dangerous goods. Fit the safety pins or caps when removing them, watch expiry dates, and dispose of expired or spent units properly — expired generators carried as cargo caused the 1996 ValuJet DC-9 fire.
- Indications and warnings: crew oxygen pressure (on the system page or a gauge) with a low-pressure alert, passenger-system "deployed/on" indication, mask flow indicators, and the green discharge disc checked on the walk-round.