More Fuelish Mistakes
Instructors, instructors, instructors – this is for you (and everyone else).
Most engine ‘failures’ aren’t – they are pilot failures. To a large extent this means instructor failures. Instructors are often not good at teaching the relationship between fuel management and life-expectancy.
And, of course, to manage the fuel intelligently you have to understand the mechanics and idiosyncrasies of each aeroplane’s fuel system. If instructors don’t get it right – how the hell is everyone else going to?
Cherokee instructors have a right – nay a duty – to grab the thigh of their pupils, m or f, when they change tanks. You have to pull their leg away from the selector so you can see that they have done it properly.
There was a recent case in the States when a Cherokee flew into a lamp pole at night. It crashed to the ground and burst into flames. Unbelievably everyone survived.
It was a training flight and the pupe switched the fuel off instead of changing tanks.
Methinks a sexual harassment charge for grabbing their leg is less stressful than sailing into a lamp pole.
I’ve told the next story before, but it has so many life-saving lessons that it’s worth telling again.
Bob Kershaw, a much decorated WW2 Spitfire pilot, was in the left hand seat, and Peter Anderson, a 1000 hour Private Pilot, was handling the maps and radios. Their wives were relaxing in the leather upholstery in the back of their new Twin Comanche. They were all in great spirits – this was their first trip in ZS-FAW.
I had done flight-tests for both of them in Peter’s Cherokee Six within the last few months, and found them both to be above average pilots.
They took off from George and headed west for Cape Town tracking parallel to the Outeniqua mountain range.
The first annoyance happened twenty minutes into the flight when the No.1 VHF packed up. No problem, they switched to VHF 2. A short while later this too began to disappoint. It was fading and not getting the range they expected at flight-level 65.
Next, the ADF needle started wandering. Again no problem – the weather was great and you just stick between the mountains and the coast. But having three dodgy radios on the first trip was starting to take the fun out of things.
Then, soon after half way, both fuel-gauges drifted to zero and stayed there no matter which of the six tanks were selected. This was puzzling because, although the auxiliaries were empty, the mains were half full and the tips were brim-full when they took off. They selected the tips and relaxed.
A couple of minutes later, as they passed Caledon both motors stopped simultaneously. There was no coughing or apology of any sort. One moment they were smooth as silk, the next – dead silence.
It was turning into a bad day – but not the end of the world – Caledon’s dirt runway was within easy gliding distance. Bob turned towards the field, made sure everyone was tied in and judged the descent beautifully.
But fate had still not finished dealing her appalling hand.
They approached a little high – as one should on such occasions – and Bob only selected gear and flaps when certain of making the threshold comfortably.
The final crunch was just that – the crunch of alclad against gravel. They had done a wheels-up in their new aircraft.
Now, when I was a hangar-rat at Wonderboom in the 60s, my boss, and mentor, Zingi Harrison, said, “Davis, when the dust has settled after an accident, there are only two things to blame. It was either the aircraft’s fault or the pilot’s. Don’t blame the weather, the dirty fuel, the crosswind or the slippery runway – those are pilot problems – the aircraft didn’t choose them.”
What Zingi said 60 years ago is still true for light aircraft accidents today.
So where does the blame lie for the broken Twin Comanche on that dusty Caledon strip? It seems pretty obvious that the aircraft was at fault.
But was it?
Here’s what really happened. That accident started two months before this flight. Bob had asked me to convert him to the twin; when I told him to expect around ten hours, he went to his buddy in East London who gave him a “quick conversion”. [Vomit].
Bob was one of those guys who are a bit too slick around the cockpit. But the bottom line is that Bob didn’t understand the machinery he was flying.
He was not used to alternator switches. On most singles the alternator is switched on with the master. Twins usually have separate switches – one for each alternator, so you can test them individually. That’s right – Bob’s flashing hand never found those two blue switches.
After that, the events were predictable. First, the radios suffered from low voltage. Then came the fuel gauges. Next, the solenoids that select the tip-tanks dropped out, so fuel feed defaulted to the empty auxiliaries. Finally, there was no electricity to extend the gear and flaps.
How could two experienced pilots get it so wrong? Well, until the engines stopped there was nothing shouting; “Warning – look at me – red flag”. Radios do pack up. Fuel gauges are not reliable. But both pilots had visually inspected all the tanks.
Electrical systems don’t wake you with clanging bells – they leave subtle clues, suggestions and innuendo. It is your job to understand these hints.
So the accident was caused by Bob not understanding the electrical system, or the fuel system. I see this as an instructor problem. I suspect Bob’s quick-conversion instructor was peering out from his hiding place in the woodpile.
Leon’s Tiger
Leon was a friend of one of my pupils at Phalaborwa. He bought a Tiger Moth from a guy who lives 30 miles inside the park. It was my job to collect the aircraft and fly it back to Phalaborwa with Leon as a passenger. Although he has bought the Tiger, he has never flown, or even sat in one before.
We take off from Letaba in the heat of the afternoon. The stifling air is red with dust from the feet of elephant and buffalo. I climb into a cooler, clearer atmosphere and level off before asking Leon if he wants to fly. Of course he does.
All is fine for a while but then he complains that the aircraft is trying to lose height. I tell him to trim back. He says that he has done that but it makes no difference. I bid him trim some more, and cast a beady eye on the duplicate trim lever in my cockpit. Nothing happens. He says he is trimming – and I say he is not. I decide to give him step-by-step instructions in this simple process, “you see the big lever next to your left leg? OK, now if you… Oh shit.”
The engine has stopped.
I tell Leon that I have control, and glance round for a landing field. We can make it to the lush green banks of the Letaba river – which is thick with hippo and crocodile – or there are a number of open patches between the thorn bushes. A landing should be no problem, but trekking through the bush amongst lions, snakes, elephants and buffalo holds little appeal.
I turn my attention inside the cockpit. A Tiger is a simple beast – there are no electrics, apart from the mag switches on the outside of the fuselage – both are ‘on’. The mixture richens itself automatically when you close the throttle. Carb-heat is also automatic. There’s only one tank – so I don’t need to check fuel selection, but habit takes my hand to the fuel cock which is out of sight below the panel. To my amazement it is switched off. I push it into the ‘on’ position and wait…and wait… and start thinking of buffalo again. Finally the engine, which has been windmilling, starts to splutter and cough. Eventually it gathers energy and becomes a healthy roar.
It’s easy to re-construct what happened. Because it was not a training flight I gave Leon no briefing, neither did I show him round the cockpit. When he thought he was trimming, he was actually switching the fuel off – both controls being near his left leg.
There are two lessons: always brief everyone, crew or passengers, who has access to any controls; and, if the engine just suddenly dies, without warning or unpleasant noises, it is almost certainly a fuel problem.
Piper got it badly wrong. Talk about briefing everyone – I do mean everyone. Those who know the Piper PA-32 Cherokee Six, Lance and Saratoga series should know where to look if you get a strong fuel smell, plus possible rough running, engine stoppage, massive fuel consumption etc.
Not sure? How about that drain that is hidden on the front of the rear spar? It’s protected by a spring loaded door that would fascinate a toddler – or even a more substantial citizen with an enquiring nature. If you open the door and then push the lever down, you will drain fuel from whichever tank is selected.
Much as I am a Piper fan, this has to be about the stupidest thing they have ever done. Not only can it be activated by someone who is out of sight of the pilot, but also because it has no practical application. Let me explain.
We drain fuel samples from each tank so we can check it is the right grade of fuel, it contains no water or crud, and it smells like avgas.
The POH claims that you can carry out these checks by watching the fuel as it moves through a section of plastic pipe.
This is BS. It’s to satisfy lazy or fat pilots who don’t fancy grovelling. South Africa is one of the few countries in the world where you can drain fuel on to the tarmac and get away with it. In the UK you would be invited to the office of the club’s flight safety officer who would raise an eyebrow at you – even if you aren’t a club member.
In Australia you would be reported to ATC by a policeman (all Australians think they are policemen). The guy in the tower will wait until you have taxied to the threshold and declared you are ready for takeoff. He will make the following call for all to hear, “Will the pilot of Cherokee VH-ABC report immediately to the airport manager to explain why he deliberately drained fuel on to the tarmac in contravention of regulation 128A, section 22 (iv) of the …”
In short – don’t do it.
Piper Navajo/Chieftain
You know how certain aircraft are associated with certain types of accident? Mention a wheels-up, and a C210 springs to mind. The early ones were guaranteed to disappoint at some stage when you selected gear down.
Mention an aircraft on its back with a broken nose wheel, and we know it’s a training Cessna. That little wheel from a supermarket trolly was designed for taxying only – not for students whose instructors have encouraged them to approach at 10 knots faster than book figure.
Mention a twin that has had both engines croak within minutes of each other and you must be talking about a PA-32 Navajo. Their fuel gauges are inveterate liars.
But why should this be? Hell, aeroplanes are enormously expensive things, and they have unbelievably expensive fuel gauges – surely one should expect some degree of accuracy – particularly when such gauges claim to predict the life-expectancy of all on board.
Even the cheapest car has gauges that will tell you within a few kilometres how far you can go on the remaining fuel – why can’t aeroplanes do the same?
Well, there are several reasons, but strangely, one of the main ones is wing design. As the wings are the best place to store the fuel, the shape of the tanks must largely conform to the shape of the wings.
Now, ideally you want a fuel tank to be pretty much the shape of a shoe box facing fore-and-aft with the float for the gauge slap in the middle. This gives you a situation where the float will read correctly in either a climb or a descent.
It will also read correctly when you bank in a turn. The thing to remember is that the fuel goes where the ball goes. So even in a steep turn the fuel will stay in the middle of the tank – as long as you have the ball in the middle – which you always do, of course.
So now we have to try fitting this fore-and-aft shoe box into the wing – and it obviously won’t go. We have to turn it sideways so it fits along the main spar – and stretch it so it holds enough gas. And squash it down so it conforms to the wing shape.
Older aerofoils had the main spar (and maximum thickness) fairly far forward so the fuel tanks were behind the spar (except for Bonanzas). Then the designers decided that a more symmetrical laminar-flow aerofoil, with the spar further back, worked better. This created more space ahead of the spar, so that’s where the tanks were put.
And of course most aeroplanes, particularly low wing ones, have some dihedral, so you end up with a long, almost sausage-shaped, tank that is tipped in towards the fuselage. Have a look at the diagram and you will understand the difficulty. On the Navajo the fuel gauge problem is so bad that even a dip-stick is pretty useless – it only gets wet if the tanks are more than ¾ full.
The diagram shows a tank that’s half full – it’s an exaggerated view of what fuel gauge designers have to cope with.
If they place the float in position A, the gauge is going to show full – even when the tank is way less than half.
If they place it in position B, the gauge will read correctly in the mid-range. But it will show full when the tank is far from full, and it will show empty when there is plenty of fuel.
Position C will give empty readings even when the tank is way over half.
Finally it’s absolutely no use looking in the tank, or dipping it unless it’s close to full.
Next time we are going to look at even more ways the fuel system can disappoint.
Instructors, I can’t do it from here – you have to understand each aircraft’s peculiarities – and then what do you have to do? Tell your pupes about them – NO. Show your pupes what the manual says about them – NO (actually you must do this). But most important – INVOLVE them by going to the aeroplane, or better still the AMO, and making your pupes get their hands green by probing every part of the fuel system.