Have you ever heard people say, “I wouldn’t fly in one of those small planes – it is not like a car where you can stop and fix it if something goes wrong?” Jim Davis walks you through some life-threatening failures that you can easily handle, or fix, from the pilot’s seat, if you understand the machinery you are flying.
You know how you get a feeling about a pilot even before you fly with them? Well my intuitions about their ability are often based how well they know what the POH has to say about the aircraft. When they are familiar with their aircraft’s systems, it tells me two things: first, they take pride in being a competent pilot, and second, they are in a strong position to cope with mechanical problems.
I am going to look at a few nasties – some of which would spell certain doom if you haven’t thought them through first. See if you can figure out the best way to cope with each before looking at my solutions.
Imagine you are flying your Cherokee or Cessna through a bit of turbulence. The nose pitches down and you pull back on the stick to correct it. “Twang!” The elevator cable snaps and the stick comes right back to your chest without having any effect.
What can you do about this so you can fly safely and land without difficulty?
Forget about trying to control pitch with power or flap. Neither of these will give you the positive control that you need to fly the aeroplane safely and land it in normal turbulence. Also forget about trying to fly it on the trim – its effect is too slow to guarantee a safe landing.
You can easily regain positive pitch control if you understand the system and give it some thought.
THE GYRO INSTRUMENTS
You are in cloud, flying on instruments when your vacuum pump blows up and you have a total failure of all your gyro instruments – the attitude-indicator, turn-coordinator and directional-gyro are all completely u/s. No, you don’t have an autopilot, and even if you did it would probably get its information from one or more of these instruments. (I should point out that such a failure is unlikely because most aircraft split the power for the gyro instruments between two sources – vacuum and electricity.)
So there you are in solid cloud with no gyros. What can you do to maintain control of the aircraft? By this I mean how can you be sure you are keeping the wings level and not going into a classic graveyard spiral? Forget about trying to keep straight on the compass, you are being bucked around by turbulence and the compass is swinging too much to be of any use.
Most people believe you need at least one gyro to maintain control of an aircraft in cloud. Can you prove them wrong and live through the experience?
BLOCKED AIR CLEANER
You are climbing through 800 feet AGL when you go through a flock of birds. One of them hits you slap in the engine cowl exactly where the carburettor air-intake is. It completely brocks the intake so there is no air getting to your carburettor. The engine dies on the spot. Is there anything you can do to restore power so you can do a safe circuit and landing?
Your aircraft has just had major airframe work done. You are the first to fly it after the re-build. It is a nice calm morning – no wind or turbulence. You take off and get to about 200 feet when the right wing drops slightly. You nudge the control wheel to the left and this immediately makes it worse. Because you are a pretty sharp pilot you quickly realise that the ailerons have been connected the wrong way. When you move the stick left, she banks right and vice-versa. Actually, if you were really a sharp pilot, you would have picked this up on the ground as part of your pre-flight or pre-takeoff checks.
Don’t imagine this can’t happen – I know of three occasions when it has. The first was to the prototype Lancastrian (a passenger version of the Lancaster bomber). It was flown by the company’s chief pilot, accompanied by the chief designer and several others. After take-off the aircraft slowly rolled inverted and dived into a pond, killing all on board.
It also happened to a Comanche which took off from Wonderboom. The pilot amazingly managed to get it as far as the down-wind leg before losing control and killing himself.
Finally, I was asked to do a test-flight on a Bonanza that had been rebuilt after a wheels-up landing. I spotted the problem during the pre-flight, but rather unkindly kept quiet about it. I was not happy about having my life put on the line by this engineer’s carelessness. I told him I would only fly the aircraft if he came with me. After much protesting he finally agreed.
I am ashamed to say that I took the aircraft to the threshold and completed the runup and pre-take-off checks before asking him if he was satisfied that all was OK. I should mention that I had had a couple of previous run-ins with this guy – we had no love for each other.
Naturally I showed him why I didn’t share his confidence in our immediate future. The man turned white, and we never spoke to each other again.
So, back to your situation where you realise that this has happened to you. Is there anything you could do so that you could make a safe circuit and landing? Simply telling yourself to work the ailerons the other way is extremely unlikely to work. Imagine you were driving your car and the steering suddenly reversed itself – I doubt that even Lewis Hamilton could handle it.
Actually there are two solutions to this potentially lethal situation – both are safe and easy to handle.
You are flying round the circuit. As you turn downwind there is a ‘twang’ as the left rudder cable snaps. You can push the pedal all the way to the floor and nothing happens. Is there anything you can do to make sure you complete the circuit and land safely? And how would you control direction on the ground?
One moment your engine is as smooth as silk and the next it’s making a terrible noise, backfiring, running extremely rough and hardly producing any power. There seems to be no major mechanical failure which might be indicated by smoke, or oil on the windscreen. You switch on the fuel-pump, try a different tank, give her a blast of carb-heat, fiddle with the mixture, confirm the primer is locked, and try different throttle settings. Nothing makes any difference – so you are pretty sure that it is not a fuel or carburettor problem. You think it may be the magnetos, so you confirm that they are switched to the BOTH position.
This has happened to me twice – on both occasions it was soon after take-off, but it could happen at any time.
Is there anything else you could try that might return sanity to the motor and take you home safely for a landing?
You are flying in cloud when you notice that the ASI (Airspeed Indicator) VSI (Vertical Speed Indicator) and altimeter are all behaving strangely. You realise that you have a static blockage. Probably ice.
This can be extremely dangerous when you are on instruments. You grope around the cockpit searching for an alternate static source, but realise that either the aircraft doesn’t have one, or you can’t find it.
Is there any way that you can return the important ones: the altimeter and ASI, back to reasonably reliable service?
THROTTLE STUCK OPEN
I have recently heard of two cases where people have found themselves with full power and were unable to throttle back because the cable had broken or become detached. One guy got himself overhead the field and then killed the engine by pulling the mixture to idle-cut-off. He then did a forced landing on the runway. Fine – he got away with it.
The other guy got the speed back by pulling the nose up, and selecting gear and full flap. He then drove the aircraft down by lowering the nose and keeping the speed at flap limiting. He eventually worked his way round on to a low, flat, high-speed approach and cut the engine with the mixture on short final. He also got away with it.
I think there is a better way. This doesn’t involve switching the mags off and on as required. That would cause massive, and potentially dangerous, explosions in the exhaust. How would you handle this problem?
SOLUTIONS ELEVATOR CABLE
You pulled back and the UP elevator cable snapped. But there is also a perfectly serviceable DOWN cable that works when you push the stick forward. So if you trim the nose well up, you can easily fly the aeroplane by using the stick in the normal way. Okay, you will be pushing against the trim all the way but who cares – you have her under control and landable.
The standard way of losing control in cloud is to enter a ‘graveyard-spiral’. It starts when a wing drops and the aircraft begins turning. If you don’t notice the turn, the next thing that happens is that the nose drops and you start losing height and gaining airspeed. You will certainly notice that something is wrong because you will hear the increased wind noise and engine revs. You glance at the airspeed, altimeter and VSI which all say are on the way down. You ease back on the stick to check the descent and this may work initially, but, by pulling back, you tighten the turn which soon causes a further loss of height – so you pull back more. Very soon you are in a screaming spiral. Your entire being is focussed on the terrifying height loss which
seems much more important than levelling the wings – even if you did notice they were not level. Sound stupid? It happens every time a non-instrument pilot loses control in cloud.
The bottom line is that if you can prevent the aircraft from turning you will maintain control. If you fly straight and keep the ball is in the middle, the wings are guaranteed to be level.
So the secret is to keep straight. The compass is no help in all but the calmest weather, and there is no gyro to keep you straight. The only instrument that can keep you straight, and save your life is … wait for it – the ADF.
Even if you are a GPS only-navigator, it’s worth having an ADF – and you can tune it to MW radio stations and listen to music.
BLOCKED AIR INTAKE
Your engine has died because the corpse of the poor little birdie is preventing air from getting to your carburettor. It is very easy to fix – apply the carb heat. This sucks in warm air from around the exhaust system – not through the air filter – so you will be back in business immediately. Obviously,
normally – to bank right you move your right hand down and your left hand up – exactly as you usually do. There can be a slight problem if you take a hand off one of the yokes, perhaps to use the radio, change the throttle setting, or use flaps. If you are flying with your left hand only, then remember that you move it down to lower the left wing, and move it up to raise the left wing – just like normal.
There are a couple of things you can do about a broken left rudder cable. The easiest is to just ignore it and steer yourself round the circuit on the ailerons – like many pilots do in any case. The rudder is really not that critical on a modern aircraft – it is there to counteract aileron-drag and P-effect. You could fly with your feet flat on the floor and your passengers probably wouldn’t notice the difference.
If you really want to use the rudder
properly, you could employ the same trick
as we used for a broken elevator cable. Remember only the left rudder
compression stroke, the exhaust stroke and at any other time – hence the backfiring and power loss. If you switch that mag off then the trouble goes away and the engine is smooth again. All you have to do is switch to one mag, if it is still rough then switch to the other one – and presto – you are back in business.
The alternate static source, if one were fitted, would simply let cabin air into the static lines and return the ASI, VSI and altimeter back to working order. They will not be dead accurate but will be usable, and their inaccuracies will be noted in the POH.
So, if there is no alternate static source we need to create one by letting cabin air pressure into the system. There are two ways of doing this. The most drastic method is to break the glass on the least useful of the three – the VSI. Cabin air will enter the system through the broken glass and the ASI and altimeter will be back in business.
A less desperate method is to put
your hand up behind the panel and see if you
if you are flying a fuel injected aircraft, the alternate-air system will do the same.
This is a very interesting one. You
have to fix it immediately because you will be very close to the ground when
you discover the problem and the aircraft will be trying to roll inverted. Any
hesitation and you are dead.
If something goes wrong – undo the last thing you did.
Luckily there are two ways of getting the aircraft under control and, taking her round the circuit for a safe landing.
The first is to centralise the control- wheel and then grab the shaft – which will give you elevator control. The trick is not to twist it at all. Now all you have to do is use the secondary effect of rudder to control roll. Right rudder initially yaws the aircraft to the right and this causes it to roll to the right. Try it next time you fly – it is surprisingly easy to fly the aircraft on rudder alone without using the ailerons at all – even in turbulence.
The second method involves taking your hands off the control wheel and then holding both wheels – your left hand on the right side of the left yoke, and your right hand on the left side of the right yoke. In other words, you grab the insides of both yokes. Now just fly broken – so we can still use right rudder. In this case the answer is to trim the rudder to the left and then fly with right rudder pressure to counteract it. Of course – you plane must have rudder trim to do this.
Finally, what’s going to happen after touch down? Well the nosewheel is not steered by the rudder cables – it has separate steering direct from the rudder pedals, so you will be able to steer in the normal way on the ground.
The probable cause of the symptoms I
described, is that a tooth has broken off a
gear wheel inside one of the magnetos.
This will upset the timing on that mag and it will produce sparks at random. In other
words it will fire during
the inlet stroke,
can feel the plastic pipe that feeds static pressure to the VSI or the altimeter. Whip out your Leatherman or Swiss army knife and sever said pipe, allowing cabin air into the system. Caution do not do it to the ASI because this has two pipes – the static and the dynamic one from the pitot-head. Murphy dictates that you will cut the wrong one and lose your ASI.
All this messing around behind the panel has to be done while you are concentrating on your instrument flying, so if you have a passenger, encourage them to do the surgical work.
THROTTLE STUCK OPEN
This is quite an easy one to handle, simply use the mixture control as a throttle. Pull it out slowly until you start losing power.
A fraction further and you will lose more power. A bit further still and you will lose all power. On most aircraft don’t be afraid of the engine dying completely and the prop stopping. If you maintain normal glide speed the prop will keep windmilling, and you will have power again as soon as you ease the mixture knob forward.
If the prop looks as if it might stop completely, say if the revs creep below about 400 rpm, then you will have to use a faster approach speed or just ease the mixture forward a fraction until she starts developing a little power.
Sometimes it is possible for the pilot to induce a serious problem by doing something quite normal. There is a very good general rule that says, If something goes wrong – undo the last thing you did.
An obvious example is that if the engine fails soon after changing tanks, go back to the one that was working. There may be a blockage that prevents you from using the new tank, or perhaps the fuel gauges are telling porkies.
I have twice been alarmed by the behaviour of Twin Comanches. The first time was in cloud during an instrument- rating renewal test. We had been doing full- flap stalls, and after recovery I was returning the aircraft to normal straight and level, when she started rolling to the right. Full left aileron was not enough to prevent the roll. To me, watching the gauges, it seemed like the artificial-horizon had suddenly failed. Fortunately the testing officer was able to spot the cause of the problem. As I selected flaps up, the right-hand flap came up but the left one remained down. He hastily hit the flap selector down and the right hand flap moved down to match its mate. We returned to base and landed without trouble.
The asymmetric flap problem is not uncommon and can happen on any aircraft where the flaps are extended mechanically, but returned to the up position by a combination of air pressure and springs. If the mechanism is not lubricated or maintained properly it is very possible that one flap sticks down when the other is retracted.
Thinking pilots keep their hand on the lever until the flaps have finished moving. This way they can arrest the retraction at the first sign of a roll. It is an equally good habit to do the same when selecting undercarriage up or down. Also, for any other operation that takes a few seconds to complete. Many airlines train their pilots to keep their hands on selectors until the cycle is finished.
When you turn the fuel pump off after takeoff, it’s a good habit to keep your finger on the switch for a couple of seconds and watch the pressure to make sure it stays in the green.
If you take the time to understand the machinery you fly, you not only earn the respect of your passengers, your fellow pilots and your AMO, but you increase your own life expectancy.