Aircraft Fuel Systems — Page 333, Lesson 421

I want to walk you through the precautions and special hazards that govern fuelling operations — this is the safety-critical side of the fuel system, the rules that keep ground crews and aircraft safe. First, the precautions after fuelling. When fuelling is complete, the bonding wires — also called grounding wires — must not be removed until one of two conditions is met. Either the filler caps have been refitted, or the pressure refuelling hose has been disconnected. The reason is simple: those bonding wires equalise the electrical potential between the aircraft and the fuelling equipment, preventing a static spark. If you pull the wire off while fuel is still exposed or the hose is still connected, you risk igniting fuel vapour. So the rule is — keep the bond in place until the fuel system is sealed or the hose is off. Now, special hazards. These are situations that pose particular danger while fuelling is carried out. The list I'm about to give you is not exhaustive, but it covers the rules to be observed. First — aircraft should not be fuelled within 30 metres, or 100 feet, of radar equipment, whether that radar is under test or in use, and whether it's in an aircraft or a ground installation. Radar emits radio-frequency energy that can induce currents and sparks, so you keep a clear 30-metre exclusion zone. Second — if the landing gear is overheated, the aerodrome Fire Service should be called, and no fuelling carried out until the heat has dissipated. Overheated brakes or gear can ignite fuel vapour, so you don't fuel until the heat is gone and the fire service has been notified. Third — extreme caution during electrical storms. Fuelling operations should be suspended during severe electrical disturbances in the vicinity of the airfield. Lightning strike risk makes fuelling unsafe, so you stop. Fourth — the use of photographic flash bulbs or electronic flash equipment within 6 metres, or 20 feet, of fuelling or vent points should not be permitted. Flash equipment can produce a spark or intense heat, so you keep it well clear of fuel and vent points. Now, marking of fuelling equipment. All fuelling vehicles, hydrant dispensers, and their components should conform to the relevant standards. Then there's a colour-coding system to identify the fuel grade at a glance. Fuelling vehicles and hydrants dispensing AVTUR — that's aviation turbine fuel, the jet fuel — will be identified by prominently placed labels with the word "AVTUR" and/or "JET A" or "JET B", depending on the grade, printed in white on a black background. Fuelling vehicles dispensing AVGAS — that's aviation gasoline, the piston-engine fuel — will be identified by prominently placed labels with the word "AVGAS" and the grade, for example 100/130 or 100LL, printed in white on a red background. So the contrast is clear: AVTUR is white text on black, AVGAS is white text on red. That colour coding prevents the catastrophic mistake of putting the wrong fuel in an aircraft. Now, there's a small table at the end of this excerpt, and it's about colour and anti-knock value. Let me read it carefully. The table has two columns — Colour and Anti-knock value — and four rows labelled a, b, c, d. Row a: Colour Same, Anti-knock value Same. Row b: Colour Same, Anti-knock value Different. Row c: Colour Different, Anti-knock value Same. Row d: Colour Different, Anti-knock value Different. This table is setting up a comparison — it's asking you to think about how fuel colour relates to anti-knock value. Anti-knock value is the octane rating of the fuel, its resistance to detonation. The table is presenting the four possible combinations of whether the colour is the same or different, and whether the anti-knock value is the same or different. This is the kind of relationship you need to reason through — for instance, AVGAS grades like 100/130 and 100LL may share a colour but differ in anti-knock value, or fuels with different colours may have the same anti-knock value. The table is laying out all four logical possibilities for you to evaluate. So to tie it together — the key safety principles are: keep bonding wires in place until caps are refitted or the hose is disconnected, respect the exclusion zones around radar, overheated gear, electrical storms, and flash equipment, and rely on the colour coding of fuelling equipment to identify AVTUR versus AVGAS. The colour and anti-knock value table is the reasoning tool that connects fuel identification to fuel performance.