REAL FORCED LANDINGS
Jim Davis
If you were ferrying a 235 Cherokee across an extensive lump of vertical scenery in the Southern Cape when the engine suddenly became intermittently rebellious, you would be faced with some serious decision making.
Would it be a good idea to pull the power right off and do a forced landing on an iffy bit of territory near the bottom of a valley, or would it be better to hope the Lycoming had sufficient fortitude to carry you across the last patch of tiger country?
Being a devout coward, I went for the reasonable certainty of a safe-ish landing in the valley rather than a nerve-twanging ten minutes of yes-no-maybe across the remaining nasties.
At the time I had perhaps 10,000 hours in Cherokees, much of which was instructing, and much of that was doing glide approaches and practice forced landings, so getting safely into my chosen field should have been easy.
Dear parishioners and instructors, the words should have are the give-away. Before reading on, take a sip of communion wine, close your eyes and try to imagine the devils that would conspire to make this forced landing a particularly hellish one. What would make it so much more difficult than all the previous ones?
Okay, here are some of the things that make training forced landings a bit of a farce because they generally don’t prepare you for the real world.
First, it’s very rare that a healthy engine suddenly stops without warning. Certainly, engines can do this – particularly when you run out of fuel, or run one tank dry. But in these cases it should not come as a surprise.
And if this does happen the following standard procedure will take care of it:
- Close the throttle – smoothly
- Change tanks, and
- Head for the landing area
Let’s run through those points.
Close the throttle. There are two main reasons for this. First, you immediately know where you stand with your aircraft – you are flying a glider. The engine is not going to give you any unexpected starts and stops that might cause you to keep changing your plans. Second, each time the engine suddenly changes between power and no power, there is a danger that the crankshaft counterweights become ‘detuned’. Here’s what Mr Lycoming has to say about it:
Detuning the counterweight system of the engine can occur when the engine operates outside of its normal range and by abrupt throttle change. When this happens the dynamic counterweights cannot follow the spectrum of frequencies for which they were designed and rapid and severe damage to the counterweights, rollers and bushings may result, culminating in engine failure.
Also, detuning can occur if the power is suddenly cut-off, such as during a simulated engine failure as required for pilot training. To avoid detuning during simulated engine failure, use the mixture control to shut off the engine and leave the throttle in the normal open position until the engine has slowed down due to lack of fuel. Then close the throttle to an idle condition. The throttle being open allows the cylinders to fill with air, maintaining the normal compression forces which are sufficient to cushion the deceleration of the engine.
Obviously, it’s fine if you close the throttle normally and gradually, but that does take away the startle factor of a simulated engine failure.
Even with a real engine failure after takeoff, it’s important to close the throttle. My mate Neville Austin had one in his Colt. He got the aircraft into a short field with gum-trees at the far end, but just after touchdown the engine came to life again at full power.
Neville found himself in a silly situation with both hands pulling on the donkey’s-dong brake and no spare hand to close the throttle.
Right, that’s dealt with the throttle – now let’s move on to the fuel.
Change tanks. Fuel starvation is by far the most common cause of engine stoppages. So it makes sense to change tanks – and bang on the fuel pump. NOTE – fuel injected Continentals often don’t like having the pump switched on during flight, so be very careful to follow the POH’s instructions about the pump. Do that NOW – not after the engine failure.
Head for the landing area. If you say; ‘but I haven’t selected a landing place yet’, then please light a big fire in the garden and chuck your license into it. You shouldn’t be flying if you don’t have a back door in mind all the time. It might not be a specific field, but it should at least be an area: towards the farmlands to my left, or away from the mountains, or away from the forest, or towards the beach, or towards the golf course.
And you don’t need to finish fiddling with the fuel system before you turn. You should close the throttle and change tanks while you are turning.
The story about converting speed to height is mostly nonsense. Think about it – the chance of your landing field being straight ahead are only one in 360, so use your speed to get you round the turn rather than gliding away from the field while you convert speed to height.
In an aircraft that cruises at 120kts and glides at 70 you aren’t going to gain much height by the time you have recovered from the startle factor and taken action.
Finally, I think it’s dubious whether trying to gain height will do any good. If you convert kinetic energy to potential energy, you don’t gain total energy. In our little aeroplanes, if the field happens to be straight ahead, simply hold the nose level until you are at your best angle of glide speed.
And this brings us to another bit of guesswork. The best angle of glide speed only works if there’s no wind. If there’s a tailwind then you need to reduce your airspeed a bit to have the advantage of the tailwind for longer; but if you glide into wind then you need to lower the nose a bit so that the extra airspeed helps you cover more ground. Exactly how much you need to change your glide speed to allow for how much wind is anybody’s guess.
Here’s a mind experiment to help you understand the wind problem. Let’ say you are a couple of miles offshore at 3000’ when the engine stops. You immediately turn towards the beach and come back to your best angle of glide speed of 70 kts. Unfortunately there is a 70 knot off-shore wind, so you will have a groundspeed of zero. You are stationary and will land in the water immediately below your present position.
However, if you stuff the nose down and glide a 100 kts you will at least be approaching the beach at 30 kts.
Obviously, if you glide downwind, you will have better range if you come back slightly to your best rate of descent speed – but no slower.
So I hope that thought will help you and your pupes remember that you need to increase your airspeed if gliding into wind.
Phew. That covers your initial actions. Just close the throttle, change tanks and head towards your field.
Next TRIM. You and I know that trim is a flying control – not a checklist item. But it’s your job to make sure your pupil uses it all the time to relieve stick pressures. If she doesn’t trim now the whole thing is going to be a dog’s breakfast with the airspeed all over the place. It’s your job to hammer this into her head particularly for a forced landing.
Plan your descent
You can do this while you are trimming.
Conventional wisdom says you should have key points at which you should be at a certain altitude. Guys and girls and instructors and pupils and captains and copilots please don’t try to use key points, and particularly don’t teach it – it does not work. For those at the back who are dozing – let me shout that out again – key points don’t work.
Yep, I know you have used them and they do work for you at your home airfield, and where you know its elevation and your altimeter is set to QNH. But for real world forced landings where you don’t know the elevation of the field and the altimeter is set to something else – key points don’t work. Promise – I’ve been there several times.
So don’t chase the altimeter; it’s a waste of precious time that you should be using for judgement outside the cockpit.
Okay now we have dealt with those initial actions – you are gliding towards an area of decent landing places and the aircraft is nicely trimmed. Here are the last steps:
- Engine
- Mayday
- Pax
- Landing checks
ENGINE
Do a round-the-cockpit check to see if you can find the problem and get the engine running again. I advise going round the cockpit rather than trying random things. This way you will know you have tried everything – there’s no chance of missing something, and you don’t have to keep wondering about it.
I suggest you start in the roof – go down the windscreen pillar to the centre console and then on to the floor and between the seats. Then you work your way from the fuel selector to the left of your knee (in most of the Piper singles) and then across the bottom panel and back across the top panel.
Have a look at the diagram. This method works for all aircraft – so you don’t have to memorise different checks for each aircraft.
I’m going to spend a bit of time on this because, surprisingly, there are a number of things you can do in the cockpit to restore either normal or limited power,
Starting in the roof – some aircraft have mag switches there, others have fuel gauges, fuel pumps, and even the throttle, pitch and mixture controls. If this doesn’t apply to the aircraft you are flying, still teach your pupe to start in the roof – one day it will apply if she flies enough types.
What is an engine failure? Actually, the answer is not that obvious. Here are six types, each needing different treatment.
1. It stops producing power but keeps windmilling.
This is the one they teach at flying schools. It’s almost certainly fuel. You have run a tank dry, or there’s a blocked pipe, or the pump has packed up. Putting on the pump and changing tanks will probably fix it.
2. The engine loses some of its power.
Try throttle friction and carb-heat first. Otherwise don’t trust the brute – it can dump you at any moment. If you are over towns or tiger country use the remaining power to get you within gliding distance of a landing place – and then sit.
3. There is a bang and the prop stops dead.
Don’t worry about fault finding – just plan your descent. Actually you glide a bit further with the prop stopped so you may need to allow for this.
4. An intermittent engine failure.
This is nasty. It can give you false hopes and lead you into deeper trouble. Remember my mate Neville in his Colt – it’s a powerful lesson that applies to any engine failure, once you are committed to land – throttle fully back. That way you know where you stand.
Intermittent troubles can be dirt or water in the fuel. Or a baffle in the silencer breaks loose and falls over the outlet pipe. Vibration can cause it to sometimes cover the pipe and sometimes not. I had the mixture cable detach itself in a Grumman Trainer. This allowed the little arm on the carburettor to swing back and forth causing random bursts of power.
You might be able to use spasmodic power to get you to a landing spot – but don’t count on anything. Sometimes it’s best just to close the throttle and treat it like a total engine failure.
5. AN IMPENDING ENGINE FAILURE.
You see, hear or smell something that tells you there is trouble brewing. While a warning is great, it can easily panic you into making a lethal decision.
A pilot and three pax took off from Wonderboom in a Cessna 182. At 400 feet the oil-cap came off covering the windscreen in black oil. The pilot, thinking he had a catastrophic engine failure, did the worst possible thing. He flung the aircraft into a steep turn to get back to the runway. Halfway round, the aircraft stalled and spun, killing all on board. Investigation showed that the engine would have kept going for a long time. So don’t let an oil leak panic you – it takes very little oil to make a huge mess.
When something starts going wrong look for supporting info to back up your suspicion.
I was flying a Cherokee at low level over the bush when the engine started to smell hot. The gauge confirmed high oil temp then the pressure started dropping. I was heading for a major failure. Fortunately I was able to land on a farm before the big event.
6. ODDS AND SODS.
I collected a toilet roll in the air intake of my Tiger Moth – don’t ask. Also had a spark plug unscrew itself and blow out of the cylinder just after takeoff over the Knysna lagoon. It caused such a lean mixture in the manifold that the engine died completely. I mention this category because machinery has a habit of confounding the wise by inventing new ways of failing.
So that deals with the engine. Remember we said after your initial actions, which had you nicely gliding towards the field with the aircraft trimmed and a plan in your mind, there were four things to do before touchdown, they were:
- Engine
- Mayday
- Pax
- Landing checks
Mayday
So we have dealt with the engine. If you can’t get it going, now is the time to make your Mayday call – but only if you have time. We all know the sequence aviate, navigate, communicate. So communicate is the least important.
Pax
Brief them – you know the drill which includes popping the door and wedging a shoe into the gap so it can’t close again.
Landing Checks
Again, you know what to do but I’m always horrified to see photos of aircraft that have had a forced landing and they often have little or no flap selected.
The Gleitch won’t give me the space to explain why the energy that has to be dissipated after a flapless touchdown is often close to double that of a full flap on-the-stall landing. In plain language a full flap landing is by far your best bet. Instructors – when you explain this, emphasise it’s because of the square-of-the-speed rule. Double the speed causes four times the damage.
Finally discuss your choices on the gear-up or gear-down debate. A lot of it revolves around high-wings tending to nose over and go on their backs if the nose gear breaks off or sinks into soft ground.
The SAAF taught us to put the gear down regardless of terrain. If it broke off that in itself would have a slowing down effect. Also in a low-wing aircraft the gear would keep the wings and fuel tanks off the ground for at least some of the landing roll.
Ultimately it’s an informed decision that you alone can make.
Next time I want to tell you about at least ten controls that you can fiddle with in the cockpit that may restore some or all of the power, as well as some surprising things to consider when you look for a field.