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’.
Text and Photographs © 2008 Gremline & Hill House
Publications, unless otherwise stated.
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