If the carburettor is the heart of your aircraft – the fuel is its lifeblood. When an engine stops without warning or prodigal noises, the problem is that it’s not getting a steady supply of nice clean fuel.

This is mainly for instructors – but fuel and its management are so poorly understood I would be foolish to assume my congregation has a firm grasp on the subject.

I’m going to tell you some true stories shortly that illustrate this. The challenge in each story is to see if you can spot the problems before I tell you.

But before we do that, let me detour for a moment. To discuss the word assume because it lies at the heart of each story. In fact it’s at the heart of most fuel problems.

The DCA/CAA employed two people who got up my nose. We will call the skinny one Swannie – because that was his name, and the other, more rotund version, I will call Mike – because that was his name.

Everyone hated and feared Swannie – he was the worst type of bullying instructor. He did my initial Com night flying test at Wonderboom in a Cherokee. It went well right up to the end of the last landing on runway 11.

We turned round to backtrack to the threshold, and thence to the Pretoria Flying Club.

During this long taxi Swannie looked at his watch and said, “Hurry it up man – I haven’t got all night.”

So I added a touch of power. It brought an immediate response from this gumboil, “Do you normally taxi at this speed?” He makes a note on the test form. Bastard.

I shut down on the tarmac with the lights of the club shining on the apron. The gyros are spinning out the last of their inertia and the Lycoming is ticking out the last of its heat. Swannie just sits there in silence fiddling with his papers. Every now and then he smooths down his Hitler-style seven-a-side moustache. He fancies himself with the ladies, but he smells like some sort of condemned food product.

I want to get out and breathe the cool night air, but he’s deliberately blocking my way and building tension. Because we are in a Cherokee I can’t get past him and escape this oppressive atmosphere.

To break the tension, I have the impudence to ask whether I have passed. He gives no sign that he has heard me. He continues chewing the end of his ballpoint. Finally he says, “I’ll think about that and let you know in the morning.”

He climbs out of the aeroplane and disappears into the night. I could cheerfully have shot him in the head.

A good instructor will shake you by the hand, even before the prop has wobbled to a stop, and say, “Congratulations man – you are now a commercial pilot.”

The other inspector, Mike, was a more portly model who also loved the power of his position. His greatest joy was to surround himself with the people he was going to test that day, and then sound off to this captive audience on his latest piece of wisdom. It was from him that I first heard the old gem, if you ASSUME you make an ASS out of U and ME.

I shudder every time I hear this bit of chichi insight. Much as the little man got up my nose, he was absolutely right – and this particularly applies to fuel.

Never assume anything about fuel – check and check again.

That’s the theme for this month’s sermon, but just saying it is not going to make a damn of difference. You may remember the words of that famous instructor, Hymorl Wright Jack, ‘Tell me and I will forget.’

Then he went on to say, ‘Show me, and I’ll remember.’

But his most famous saying was, ‘Involve me, and I will understand.’

I’ll involve you by telling you some stories about pilots assuming the fuel situation was okay. And you, dear instructor, will then involve your pupes by showing them around different aircraft and pointing out their fuel drains, selectors and idiosyncrasies.

So let’s cast off and get under way by telling you that I am the red-faced, and almost dead, hero of the first story. I made an assumption about an Aztec’s fuel system, and it nearly cost me my life.

See if you can spot the trouble in each story before I tell you what went wrong – it won’t be easy.

Aztec plumbing.

It’s a SAAF Commando flight, which means I have to don my lowly, second lieutenant’s flying overall and shiny shoes. I am to fly a red, long-nosed, Aztec from George to PE. I must refuel at the SAAF base and then head off to collect a General from some secret location and fly him to another secret L. Everything’s a secret to the military mind.

After refuelling I do a proper preflight, including sampling all four tanks and the fuel strainers for water.

There’s a strong easterly so I take off on 08 and head out across the bay. All goes according to plan until I’m climbing through 5 000ft when I notice the EGTs on the left engine are way too high.

This is extremely odd – it is a cool day, I am using reduced power – 25/25, the mixtures are slightly rich and the other engine is fine.

I keep a beady eye on the gauge. Then I notice that the CHTs are also rising, and soon the oil temp starts to imitate its companions. I do indeed have a hot engine – not dodgy gauges.

I am about to reduce power when the aircraft swings violently to the left. The motor splutters, wakes up, quits and splutters some more.

This is not a heart-stopping event. I have plenty of height and the airfield is only 30 miles behind me. I throttle back, feather the prop and turn for home.

While tidying up the cockpit and shutting down the systems on the failed engine I am dismayed to see that the right engine seems to have been infected by its brother’s fever – it’s temps are also increasing.

What moments ago had seemed to be a mischievous gremlin, has suddenly become a fire-breathing monster who is threatening to hurl us into the sea.

My fears are justified. Both engines are indeed suffering from the same malady so I re-start the left. I can only hope that between their alternate banging and wheezing they might have sufficient urge to get us home.

I put both props into fine pitch, both fuel pumps on, both mixtures fully rich and both throttles fully forward.

I want to cling to whatever altitude we can manage until we are much closer to home.

Fuel pressures and flows seem to be behaving normally and the possibility that four magnetos would all decide to play silly-buggers in unison is beyond reasonable.

We struggle towards the airfield at 100 mph. Sometimes when both engines synchronise their silent periods I know we will splash down in the ocean. And occasionally, when they pull together, we gain a few hundred feet and my hopes soar.  

They seem to have conspired to supply only the minimum impetus necessary to keep us in the air.

‘Come on Clive, put your back into it.’

‘You put your bloody back into it mate, I have got a fever – I’m hot as hell.’

‘I have a cough like you can’t believe so don’t expect me to do all the heavy lifting.’

‘FFS do you want to drown us all in the sea? We are nearly there – just pull you idiot.’

The fact that I am here, pecking at my keyboard, tells you that we did indeed survive the spluttering and swinging to the threshold.

PE lets us land downwind on 29 because that’s exactly how far these invalids are prepared to go. If we had lost another 50’ the site of our demise would have ironically have been the hangars of SAAF base that had so recently refuelled us.

The problem? All four tanks contain huge quantities of water.

I am much puzzled. After refuelling I had allowed a few minutes for everything to settle, and then drained in the normal way. Why had I not found the water? Simple – I didn’t understand the system.

Actually there’s not much to understand. The Aztec has three fuel drains in a cluster under each engine. One drain is for that wing’s outboard tank, one for the inboard tank and one directly on the filter bowl.

A little thought would have told me that there must be a longish pipe from each tank to its respective drain. That’s right – you need to drain all the fuel out of the pipe before you have a sample of what’s in the tank.

This taught me that when flying an Aztec, or any aircraft where the drains are not directly on the bottom of the tanks, you need a big Coke bottle to do the draining.

I ASSUMED I was sampling the tanks – I didn’t think it through.

Later I learned that PE had had serious floods overnight and that the fuel guys at the military base hadn’t got round to dipping the underground tanks.

First thing every day they should put some green gunge called Kolor Kut’s Water Finding Paste on the end of a dipstick. If the paste contacts water it immediately turns red. Again I assumed this had been done – and I was wrong.

235 Crossfeed

It is 1964, the ink is still wet on my commercial licence and I am about to crash a 235 Cherokee that’s as new as my qualification, in perfectly clear weather.

We are at Hotazel, a manganese mining town in the shimmering desert of the Northern Cape. As the wheels leave the ground the right wingtip tries to bury itself into the sand. Full left aileron and plenty of rudder barely keep the tip-tank off the boulders. We have swung to the right of the runway so I don’t have the option of landing again. Easing back tightens the turn and kills the speed, robbing the ailerons of the airflow they need. Easing forward is not an option.

I prod the last bit of left rudder and gradually – very gradually – sanity returns. The wing slowly rises, the airspeed creeps up and the aerodynamics arrange themselves such that we can inch away from that blistering surface.

I am at first alarmed, then much puzzled. What is this force that tries to invert us?

It was fine when we landed a couple of hours ago. Since then I have been parked in the shade of a baobab tree and have not left the aircraft. There have been no people, animals or vehicles near us. We did not hit anything on takeoff in Kimberley, nor while landing here. The flaps have not gone asymmetric.

The aircraft has done less than 100 hours in total, so I doubt there is any structural or mechanical failure. I can see nothing unusual on the wings or that part of the tailplane that is visible from the cockpit. I search inside. I either have to cure this disease or land back at Kimberley with a touch-down speed of more than 100mph.

Suddenly I see the problem. There is a row of four little rectangular fuel gauges, the two right hand ones are brim full while the left tip is stone empty and the left main has about 5 gallons. I select the right tip and gradually over the next hour the aircraft becomes more flyable.

There were three reasons for this atrocity.

First, a faulty selector allowed the fuel to cross-feed and overflow on to the ground while we were parked on a slope. Second, if my pre-takeoff checks had been less casual I would have noticed the warnings of those four little gauges. Finally, because I knew nothing could go wrong on the ground, I skipped the pre-flight inspection – something I have never done since.

I ASSUMED nothing could go wrong while we were parked.

Beware – this is an unusual problem on Cherokees – but a daily hazard on 100 series Cessnas. I will explain later.

Dangerous bugs

My very first aviation job was as hangar-rat for Placo, the Piper agents, at Wonderboom airport, just north of Pretoria. My status was extremely humble and my immediate boss, Zingi Harrison, was the best and most knowledgeable pilot in the world.

He wore a bowtie at all times and loved to tell a story. When Zingi spoke, it was always worth listening.

On this particular day, the big boss, Mr Piet van der Woude, had sent Zingi in a single Comanche ZS-CWG, to Virginia Airport, in Durban. The object was to collect Mr Piet’s 80 year old mother, his stunningly beautiful wife Myrtle, and two infants.

Zingi left Wonderboom with minimal fuel. He filled the tanks in Durban before loading his precious cargo. He was on his way back at flight-level 105 and half way across that nasty bit that is all mountains and clouds.

You know that cold feeling in your stomach when you look at the scenery below and think, no one likes an engine failure – but I really wouldn’t like one now? Well that’s when the engine abruptly stopped, without apology – no warning, no splutter or cough – just silence. The kind of silence which instantly wakes sleeping grannies, beautiful wives and sticky infants who have all been put to sleep by the thin air and the drone of the Lycoming.

Zingi was baffled. He hit the fuel pump and changed tanks, even though the right main, that he was using, showed almost full and had given good service for the last twenty minutes.

The way Zingi explained it, the telling took longer than the flight. Here’s what happened. When he refuelled at Virginia, he didn’t notice how much fuel went into each of the six tanks. If he had he would have seen that the right main, although nearly empty, accepted only three gallons before it was full.

There was good reason for this. A bug, in Pretoria, had made its muddy home in the breather for that tank. This meant that while Zingi was using it on the outbound flight, the bladder fuel-cell was being scrunched into a little ball as the fuel was sucked out of it.

Obviously at the pumps it took very little fuel to fill this now prunelike container. When Zingi peered into it during the preflight inspection the tank looked full, and the gauge showed full because the float had been carried to the top with the scrunching.

This is not just a story about a guy with a funny name and a bowtie. Mud-bugs are still around and so are bladder-tanks – it can happen to you tomorrow.

The lessons are plain. Make sure that what goes into the tank seems sensible, when you check for bugs – really check, and make sure you understand the system. Many Cessnas have only one breather for all the tanks – so you may not be as lucky as Zingi.

If Zingi, in addition to looking into the tanks, had checked the receipt from Mr Mobil, he would have seen that something was wrong.

No. He ASSUMED the tanks were all full after he looked into them.

This fuel thing is so important that next month I have more stories about people making assumptions and getting it wrong.