Gremline Flight Safety Report: Forced Landings in Light Aircraft

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Forced Landings in Light Aircraft

Each year sees a fairly constant number of fatal accidents to UK GA aircraft while attempting forced landings after engine failure. A proportion of these fatal accidents involve a stall/spin loss of control close to the ground. These accidents are avoidable.


Introduction
Glider pilots manage a successful engine-off “forced landing” at the end of each sortie. Quite a few of these landings are into previously unseen fields. The vast majority are successful. Why do pilots of powered aircraft apparently find the same exercise so difficult? I suspect the answer lies in the glider pilots’ training and the fact that they renew their skill on each flight. And perhaps the totally variable drag provided by the airbrakes on most sailplanes make the final approach more easily controllable than the two or three-position flaps available to the pilot of a powered GA aircraft that has suffered an engine failure. But if my assumption is correct that glider pilots’ training and their regular use of “forced landing” techniques point the way to a successful forced landing, then training and practice are the powered pilot’s keys to success. The fact that glider pilots are trained to spin, to recognise incipient spins and recover from spins, also has some bearing on the subject.
This article will examine a simple and well-proven technique that, with regular practice in your own aircraft, should make a successful forced landing after an engine failure much more likely than the all too frequent stall/spin crash that is the sad result of many attempted forced landings in GA aircraft.
A valuable aphorism is that an exceptionally skilled pilot is one who avoids situations that demand an exhibition of their exceptional skills. So it is stating the blindingly obvious that it is much better to avoid a forced landing than to demonstrate your skills by performing a successful one. I will begin with a review of some of the more likely causes of a forced landing in a single-engined GA aircraft, and a few thoughts on how to recover the situation before you have to continue all the way to the ground.

 


Likely Causes of a Forced Landing
A discussion of the likely causes of a forced landing should encourage pilots to at least consider these possibilities during their pre-flight planning. The best place to plan a forced landing, and to think about your actions in the event of an engine failure, is in the unhurried atmosphere of your favourite armchair. The more time you spend pre-planning emergencies while still on the ground the more likely you are to get it right in the air.
Loss of engine power can occur suddenly – or creep up on you in a gradual and sneaky way. The latter is more difficult to spot immediately, and the reduction in power may have progressed to quite serious proportions before you are triggered into doing something about it. Regular monitoring of your engine instruments without detriment to your lookout takes practice that becomes easier as you develop your flying skills and experience. Listening to your engine rather than chattering to your passengers or on the radio can help with engine monitoring. Personally, I would never wear a noise-limiting headset in a GA aircraft because I believe they are unnecessary and only isolate you from many valuable aural clues about the performance of your engine and airframe. Fashion accessories do not contribute to safety.

 

Carburettor Icing. Carburettor icing will sneak up on you and may be indicated by nothing more than a very gradual and almost unnoticed reduction in manifold pressure or a small drop in engine RPM, depending on your aircraft. A constant speed propeller can mask the onset of carburettor icing. If you notice a slight power loss then try to think “carb icing” immediately. A careful study and understanding of the excellent carburettor icing information published by the CAA will give you the knowledge to control this potential killer (and see our July 2008 article Carburettor Icing in General Aviation Aircraft). It is not overstating the case to call carb icing a potential killer. Just look at the fatalities over the past few years. A throttled-back descent is a great place to experience carb icing, so a wise pilot will think “carb icing” in their pre-descent checks. Is carb icing more likely in summer or winter? How is it affected by relative humidity? How long is long enough for an application of carb heat? Is your aircraft any different from others?

 


Fuel Problems. There are few valid excuses for running out of fuel in the air. Many GA aircraft are fitted with totally unreliable fuel gauges and only a foolhardy pilot would rely totally on the fuel gauges to determine their safe endurance. You should have plenty of time before takeoff to KNOW exactly how much fuel is in your aircraft. You should have a fairly accurate knowledge of the actual fuel consumption of your aircraft (not what it says in the Manual) so you should know how many hours and/or minutes the engine will run before starvation occurs. When you record your start-up time also record the time you will reach the expiry of your safe endurance.
Fuel contamination is probably slightly more forgivable than fuel starvation. There are checks and actions to be completed on the ground that should reduce the chances of fuel contamination in the air. Mis-fuelling is a possible cause of contamination. Are you sure you are about to fill up with the CORRECT fuel? It’s your own responsibility to check. I have watched pilots draining fuel from the tanks as part of their pre-flight inspection, but have had some very odd answers when I ask them to explain EXACTLY what they are doing! Sniffing your finger is not a good fuel check. Have you even been shown just what water in a fuel sample looks like? Why not ask for a demonstration? I think you’ll be surprised. While on the topic of water in the fuel, how about your filler caps? It is easy for rain to get into fuel tanks with recessed over-wing fillers if the caps do not fit properly or if the filler cap washers are perished or damaged. A new set of washers cost less than a new aircraft.
Take care about tank selection, in the air and on the ground. Gross fuel imbalance can occur in some types if you park them on a slope with a wing-down attitude. You can, with a little thought, correct this before takeoff. Be sure to select a tank with plenty of fuel for your takeoff and climb. Just because the engine starts on the ground does not mean the fuel system is connected to ANY tank. Several aircraft types will have enough fuel in the lines between the tank selector and the engine to allow you to get to an awkward height before the engine stops --- because the fuel is selected to “OFF”.


Mechanical Problems. Mechanical failure of the engine or the propeller can be sudden and dramatic. Making absolutely sure that the engine and propeller on your aircraft are maintained correctly and on time will reduce your chances of having a disaster. Has the engine been turned over regularly as required by LAMS/LAMP? It’s wise to examine all the available publications and directives relating to your aircraft whenever it is undergoing periodic servicing because it is all too easy for some recently published requirement to be missed. When you open the cowling for the daily inspection make sure you really look at whatever it is that you are supposed to be checking. Don’t let your check become a routine and meaningless mantra to be gabbled through without thought. Checks will not keep you safe – seeing something amiss may do so. If you are going to check the engine oil then do it with care. Has the engine begun to use more oil than usual? Why? The contents may be up to the mark, but is the colour and texture of the oil also correct? What is correct? An experienced engineer will always provide advice.
If the prop decides to fly off into the distance you can forget about it and concentrate on flying the rest of the aircraft. If your variable pitch propeller decides to stick in coarse pitch you will need to plan your letdown, approach and landing with care. An attempted go around will probably be interesting.
If you suffer a catastrophic mechanical engine failure (broken conrod?) then shut the engine down without delay to avoid further damage from vibration. I was once in an aircraft with four big radial engines when one of them disintegrated. The whole engine, propeller and cowling shook off the wing and fell clear before anything could be done. The aircraft remained under some sort of control. A single engined aircraft with the same sort of failure would be poorly placed.

 


Electrical Problems. Electrical problems can, like carb icing, creep up on you with stealth. Do you really understand the functions of the voltmeter and the ammeter? Are you sure? It is too easy to assume that if the engine starts then the electrics are OK. I have seen otherwise intelligent pilots use jump leads from a car to start an aircraft with a dud battery – and then take off. A discharged battery is warning you of something wrong with the electrical system and it will not recover during flight after a jump start. Replacement by any old battery available is not a sensible course of action. The care and maintenance of aircraft batteries is poorly understood by most pilots and is often the root cause of electrical problems. It could save a very costly accident if you learn more about how to care for the batteries in your aircraft. “Fit and Forget” is not the way to do it.
More information is available on this web site, published in November 2007 under the title
The Use and Abuse of Aircraft Batteries. It could save a lot of grief.


Airframe Damage. Collision is the most likely cause of airframe damage. Collision on the ground can be just as dangerous as collision in the air. There was a sad case where a pilot taxied into a hay bale on the airfield but continued to take off after making an external examination of the wing. The wing folded in flight and the pilot died. If you have a brain failure on start up and begin to taxi with a tie-down lump of concrete attached, don’t just unhitch the rope and continue. The aircraft is almost certainly damaged. If you have even a ‘slight’ collision on the ground, no matter how slight it may appear to you, the aircraft is unserviceable until proven otherwise by inspection by a qualified engineer. If you have a collision in the air your aim must be to get on the ground, under control, as soon as possible. Reduce speed to a minimum safe figure, check the handling very tentatively, and land at the nearest suitable spot. Do not play at being a test pilot to check the stalling speed. If the aircraft is controllable at an acceptable approach speed, that’s all you need to know. If you are faced with a faster than normal approach speed then you will have to find a longer landing run with room to allow your speed to decay prior to touchdown. If the aircraft handling appears to be unaffected after a collision then you must not assume that all is well. The airframe integrity has almost certainly been degraded and some vital part may fail gradually over the next few minutes. Reduce the airframe loads as much as you can and land as soon as possible. A recent fatality occurred when the airframe failed several minutes after the collision.
Airframe damage can occur after an encounter with severe turbulence or if you have lost control (in cloud?) and exceeded Vne. You may have read about Va in previous Flight Safety articles. You should know and OBSERVE the Va limitation in turbulent conditions, or when you are likely to encounter turbulence. It doesn’t make any sense to penetrate a layer of cloud greatly in excess of Va. Don’t know what Va is for your aircraft? Find out.

 


The Forced Landing
Despite your best efforts you are suddenly faced with having to perform a forced landing. The first point to make is that the objective of a forced landing in a light aircraft is to walk away from the landing. If you and your passengers do that then you have been successful. If the aircraft is undamaged then that’s a bonus.


IMMEDIATE ACTIONS

 

Fly the Aircraft: You must concentrate your mind on flying the aircraft as accurately and smoothly as you can. Low inertia light aircraft will lose speed very quickly after an engine failure. First, trim the aircraft for the best glide speed. Many instructors teach “Convert speed to height”. I think this is a waste of time and effort in most general aviation aircraft. How much extra height are you going to gain? How much extra range will that give you? If you are thundering along in a F16 at 600 knots at 250 feet and the engine stops, certainly convert that speed to height. If you are puttering along at 120 knots at 2000 feet then you have more urgent things to do than try to gain an extra quarter mile in gliding range. If your best gliding speed is 60 knots and your rate of descent is 1000 feet per minute then your gliding range is one mile per thousand feet. Even if your rate of descent is only 500 feet per minute you are only going to glide two miles per 1000 feet in still air. These ranges will be reduced by any headwind component during your descent. By the time you get to 1000 feet above the ground you MUST have chosen a field and be established in your landing pattern. So, from 2000 feet you have somewhere between one and two minutes (at best) to have sorted everything out and made all the right decisions. Leave the height while the speed reduces to your gliding speed and you will have converted speed to thinking time. Thinking time will be your major shortage after an engine failure at 2000 feet. That’s another good reason to cruise as high as is reasonable.


Sort the Problem: If the cause of engine failure is not obviously mechanical then go for carb icing and fuel starvation as the most likely two. If you have just made some sort of selection (changed tanks?) then check that you have made a correct selection. If you can’t sort the problem then concentrate on the forced landing.


Mayday: Call on the frequency in use if you are in contact with someone, otherwise call on 121.5 Mhz if you have time to spare. Flick your transponder to EMERGENCY. But above all, concentrate on flying the aircraft at the best gliding speed.
“Turn downwind for range?”. This is another old chestnut in my opinion. If you are at 5000 feet above ground level and there is a 20 knot wind blowing then turning downwind may give you an extra mile over the ground before you are committed to your landing pattern. It’s good to have the surface wind stored in your memory, but you know this from your pre-flight planning. If you can find a suitable landing run within 30 degrees of the assumed surface wind, that’s good enough.


FLY THE AIRCRAFT: Don’t allow yourself to be distracted from your primary task, which is to remain in control of the aircraft. It’s pretty pointless to go through pages of checklists, make lots of radio calls, pick a perfect field and then spin in because you forgot to fly the aircraft.

 


Field Selection
The ideal forced landing site is an active airfield which just happens to be almost directly below you when the donk stops, but that’s unlikely to happen so you are faced with choosing one from those well within gliding range. Wouldn’t it be silly to have an engine failure in the visual circuit only to discover that your circuit is so huge that you cannot glide to the airfield? It’s pointless selecting a beautiful field on the far horizon. You’ll be surprised just how short is the distance you can glide before you MUST commit yourself to a landing. Choose a field WELL INSIDE your wingtips. Practice Forced Landings are usually flown with the engine at idle, but that does not necessarily mean that you have zero thrust. You may be benefiting from some thrust – or suffering excess drag. Don’t be misled into aiming for a field you are not going to reach with enough height to fly a controlled approach and landing.
The Royal Air Force taught their “Bulldog” and “Chipmunk” pilots to select a field inside the wing roundels, which means a field within about half span. That gives some room for correction.
Your field selection criteria, assuming you have a choice, include five Ss. Size, Surface, Shape, Surrounds and Slope. Size; the bigger the better, but you can land successfully in a remarkably small field when you keep in mind that the aim is to walk away from the resultant landing. Slowly into the far hedge is much better than quickly into the near hedge. Surface can be discussed until the cows come home. A recently cut 1000 yard long corn field (without bales) is probably ideal. A soggy ploughed field is not an ideal first choice. If possible, avoid tall and strong crops like sweet corn or brussels sprouts and tall grass or corn ready for mowing. You may be already committed to landing before you realise the surface is less than ideal. TOO BAD. Concentrate on flying the aircraft and making a controlled arrival. I once had an engine seizure in a Turbulent (G-APNZ) and selected a beautiful level field about the same size as Heathrow, and right beside a main road too. When I was at about 200 feet, peering past the rigid little prop, a gentle breeze sent deep waves rippling through the waist high grass that I hadn’t spotted in time. The Turbulent clattered across the tops of the grass and sank gently onto the ground as I eased the pole fully back. I found myself sitting in the cockpit of an undamaged aircraft, with my head just above the top of the waving grass. A little placard on the instrument panel read “All aircraft will bite fools”. The most difficult part was finding the Turbulent again after the “Rescue Team” arrived to load the plane onto the back of a lorry for the trip back to the airfield.
The Surrounds of your selected field should, ideally, include access from a road, no power lines or telephone cables, no high trees and preferably with a pub nearby so you can wait in comfort for the arrival of the experts. Don’t worry; there’ll be plenty of experts!
Slope is quite difficult to judge until you are probably too close to do much about it. If you have to land on a steep up-slope you will need a big attitude change on touchdown that will consume airspeed with the risk of stalling into the ground. Trying to land on a steep down-slope could involve nothing more than a low and slow flypast before you vanish into the scenery. Try to avoid steep slopes. If you have no choice but to land on sloping ground then an up-slope is better than a down-slope. An up-slope will reduce your ground roll. The only problem is that the aircraft may tend to roll backwards after landing. Leave the brakes on. Next time you are flying across country study the ground below and try to judge the slope of the ground. There are clues that you can spot with practice. If you are crossing rough or mountainous terrain then perhaps an extra thousand feet on your chosen cruising altitude is wise. Slight detours around particularly difficult terrain in a light single engine aircraft could reduce your chances of ending up in a crumpled heap of aluminium. Think about the terrain below and the conditions down there, particularly in winter. “Scud running” is stupid at any time. Doing so at low level across rough terrain is unforgivable. I remember something my basic instructor told me as we approached the Canadian Rocky Mountains, He said, “Remember, a 180 degree turn is often the best manoeuvre.” This applies EVERYWHERE, sometimes before you even get into the aircraft.
The other point to have in mind is the wind direction. Landing into wind will reduce your groundspeed and the length of your ground roll. If the aircraft is obviously drifting strongly then you have got it wrong but for goodness sake don’t forget the prime directive –
FLY THE AIRCRAFT.


The Technique

We have finally come to the meat of this long, wandering article. How do you judge a forced landing so as to make the flying as easy as possible? The first step is to select a field, as covered above. Now, how do you guarantee to arrive in that chosen field with minimum fuss and maximum possibility of getting it right? The answer can be found in the following article ‘ The Constant Aspect Approach’.

 

 

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