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Forced ApproachTransport Canada has a very good chapter on Forced Approaches in the Flight Training Manual (chapter 22) you should start by reading that. TC also has a PDF explaining the High-Key Low-Key forced approach procedure. We have also written some information about Forced Approaches in the FTM, please read that also. Forced Approaches will be your first dual lesson after being checked out in the C-172 so review the expectations in the AVIA 100 section of the Program Manual |
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Make sure you can answer the following questions:
Your flight instructor will tell you to look for a nice grass field to land in. If you can find one then go for it. But it is good to know that any flat surface will be survivable. The airplane to the right landed in a plowed field. The pilot walked away without serious injuries. The airplane is of course seriously damaged, but that is minor compared to the potential for loss of life. The Approach Matters MostWhen selecting a field to land in the approach to the field matters more than the field itself. Avoid fields that require you to clear obstacles on short final such as trees or power lines. Bottom line - pick the field that has the most open - easy to fly - approach. If there are lots of fields that meet the above criteria, then pick the sod farm not the plowed field :)
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If you are lucky you will find a 10,000 foot paved runway right below you if you ever have an engine failure. Those pilots who have been that lucky don't show up in the accident reports because they walk away without incident. But, you might not be that lucky.
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Surviving a crash-landing is mostly a matter of energy dissipation. In other words, if you hit something that stops the airplane instantly you WILL NOT SURVIVE. But, if you stop over a distance as little as a few feet (depending on the speed of impact) you can survive. In cars air-bags are designed to "stop you" in six inches, rather than instantly and that small amount makes the difference between survival and death. In a forced approach situation your ONLY concern should be to survive. Don't worry about damaging the airplane. It can be replaced - you can not. The airplane to the left bounced off the roof and hit the tree. With a good seatbelt and shoulder harness this is survivable. Soldiers have a grim saying that "you never hear the bullet that kills you." In a plane crash if you hear three or more bangs as the airplane hits the ground your are probably going to live through it. The banging sounds represent parts of the airplane impacting something on the ground and with each impact energy is dissipated. If the first impact was fatal you wouldn't be there to hear the second one.( I call this the Big Bang Theory.) So each "small bang" brings you closer to stopping and escaping.
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If the above makes sense to you then as a pilot you should look for things that will make "small" banging sounds when you hit them. For example small trees, fences, shrubs, etc. Avoid things that are going to make one BIG bang that you won't be around to reflect on, such as the side of a building, a large rock, a mountain bluff, etc.
"Speed kills" is the mantra of the Police regarding automobile driving. But it applies to crash survival as well. The energy of the crash is proportional to velocity squared. I.e. if you land twice as fast there is four times as much energy, or to put that the other way around you can quadruple your chances of survival if you cut the impact speed in half.
Single engine airplanes are required by law to have a stall speed of 61 KCAS or less precisely because of crash survival considerations.
Unless you are conducting a forced approach to a runway it is mandatory that you land at the lowest possible speed, which means full flaps and just above the stall speed and into wind at touchdown. You will need to practice judging the "float" so that you can control your touchdown point and land at minimum speed.
It is also important to understand that your body's ability to "absorb impact force" varies with the axis. In other words you can take a lot more force perpendicular to your spine than along it. If you land with a high vertical speed you will compress your spine and either kill or cripple yourself. But a much larger force across your chest - fore to aft - may do little more than leave a bruise.
It is important to use your shoulder harness for survival. Its purpose is to restrain your upper torso and head from hitting the instrument panel. If your head hits the panel at anything more than a few knots the blow will be fatal. Therefore ensure your seatbelt and shoulder harness are tight before landing.
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The accident about to happen at left is not survivable for two reasons.
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The same problem can happen if you crash into the tops of tall trees. According to the "Big Bang Theory" the crash will be survivable, but the subsequent fall 100 feet to the ground likely won't be. It is therefore wise to avoid striking anything more than a few feet (less than 10 feet) above ground level. The airplane to the right bounced off the tree tops, which was survivable, but then "fell to the ground" on the nose, which is not survivable. |
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Even something quite low, such as a fence could be a killer if you let it flip you on your nose. In this case its not the impact with the fence, but the one with the ground that will be fatal. A fence is potentially an excellent barrier to crash into, but you want to hit it with the airplane's wheels on the ground. That way there is no opportunity to "fall on your nose."
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Land in Water or Not?Here in British Columbia there are a lot or rivers and lakes and a lot of very rugged ground, so it is sometimes tempting to consider a landing in the water rather than face a mountain side with trees and rocks. It must be granted that neither option is especially appealing, but if you examine the accident stats for landings in water the vast majority end with at least some, often all, occupants dying POST CRASH by drowning. Landing in water may not be fatal. In accordance with the principals discussed above you will likely dissipate energy over several feet and thus survive the landing. But the airplane will quickly sink and in most cases will be upside down. The disorientation this causes frequently results in many or all occupants not getting out of the cockpit. If you are committed to extended flight over water, such as a ferry pilot on an oceanic crossing then you should seek out special training in under water escape. There are courses available for this: If you have not had this specialized training I suggest you move heaven and earth to avoid landing in the water. |
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We believe there are three broad methods you can employ to make a forced approach:
Of the above the figure eight is the most commonly taught, it is also by far the worst choice in most cases. There is a saying that you should "not put all your eggs in one basket." The idea being that if you drop the basket you will loose all your eggs. As commonly performed the figure-eight procedure puts all the eggs in one basket and then carries the basket balanced on a stick. If you do it perfectly you will be alright, but one misjudgment and you are too low or too high with no opportunity to recover.
Lots of pilots make forced approaches every day. Only a few are emergency landings following an engine failure, the vast majority are made on purpose, for example:
The first rule of real forced approaches is to maintain an "energy reserve." An energy reserve means that you have:
"Extra" means: more than the minimum needed. It is usually wise to have both extra altitude AND extra speed.
Glider pilots approach with partial spoilers extended and several knots above the maximum glide speed. That way if they encounter a downdraft on approach they simply retract the spoilers and if necessary slow to maximum glide speed. Using this method they seldom "come up short."
The Space shuttle glides from orbit to landing at supersonic speed slowing to the best glide speed only in the last few minutes. Energy reserves are tracked continuously by a computer monitoring system and "bled-off" gradually as the shuttle approaches the runway.
The X1 and X-15 landed "dead-stick" after each flight. The main advantage they had was the incredibly long runway at Edwards AFB but they also approached at far above the maximum glide speed.
IT is CRITICAL to remember that crash survival requires landing at the lowest possible speed. Therefore the recommendation to maintain an energy reserve during the approach MUST be tempered by the advice to eliminate the reserve in the last minute of the approach. The flaps must be extended and the airplane slowed to the lowest possible speed prior to the landing - unless the available landing area is safe for a higher speed landing (for example a runway.)
Power pilots usually are taught to maintain energy reserve only through altitude while gliding at the minimum safe - i.e. maximum range glide speed. I believe that the maximum range glide speed should be thought of as the minimum speed to glide at - but there is a lot to think about when choosing a speed to glide at. Power plane pilots are taught to quickly slow to the maximum glide speed as soon as the engine(s) fails. There are two good reasons for this:
But, as soon as you do have a landing sight selected and Mayday call made it is important to establish and maintain an energy reserve. Position the airplane well within glide range of the field and add 10 to 15 knots above the maximum range glide speed.
It is important to know that the glide speed in the Pilot Operating Handbook is only correct in zero wind. If gliding into a headwind maximum glide range is obtained at a higher speed. Increasing airspeed by approximately half the wind speed will result in the maximum glide range.
The simulation at the bottom of this page will demonstrate this effect.
For a deeper discussion of this phenomenon see the textbook Aerodynamics for Professional Pilots
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Examine the situation the the left. The engine has failed and the airplane is at the "start point." Also assume the airplane is gliding at the maximum range glide speed. The pilot has arranged so that the flight path shown will take the airplane to the landing point. The metaphor of the eggs all being in one basket was mentioned above. In my opinion this pilot is putting all his eggs in one basket. If his judgment is correct he will land successfully, but if he discovers a few seconds after the start point that he is too low there is no way to recover - an impact short of the field is inevitable. If you are thinking that you would not use this strategy take a look at the back story.
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Two-Basket ApproachThe diagram to the left shows a strategy equivalent to putting your eggs in two baskets. The pilot first targets a key-point abeam the landing point and attempt to reach it at 1000 agl. However perfect success is not required. The pilot now has an opportunity to recover from less than perfect gliding as follows. If high at key point:
If low at key point:
Limitations of This StrategyThe biggest problem with this strategy is that it can only be employed if you have sufficient altitude to maneuver to the 1000' agl point. If you don't have the required altitude you will have to make a direct approach to the landing point and live with having all your eggs in one basket. The second limitation of this strategy is that it supposes that you can estimate the ground level. However, this is not really a limitation since the pilot does not need to target a specific numerical altimeter reading at the 1000' agl point. Instead the pilot should, in accordance of the principal of maintaining an energy reserve, judge the approach so that a definite reserve of altitude and speed is retained to the 1000 ' agl key point. |
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High-Key, Low-Key (Three-Basket Approach)The diagram to the left shows a strategy in which the pilot has two key points to aim at. The first is near the desired landing point, the next is abeam the landing point. The Flight Training Manual has a formula for these altitudes, but for most light aircraft 2000 agl and 1000 agl, approximately, are good choices. The strategy is to "hit" the first key point, known as High-Key at 2000' agl. From there a rate-one turn will bring the airplane abeam the landing point at 1000 agl. From there a landing is easy to make. If my advice regarding energy reserve is followed the airplane will glide at about 10 knots above maximum glide speed while performing these maneuvers. In accordance with the need to land as slowly as possible the pilot will begin to extend flaps and eliminate the energy reserve on the base leg - especially if the landing area is rough. By the time the airplane reaches the touchdown point it should be just above the stall speed. |
The simulation below allows you to experiment with the High-Key / Low-Key Forced approach procedure.
Fly the airplane using the arrow keys. Best glide speed is 65 in zero wind (remember to increase speed with a headwind.)
A blue circle will appear. This is your radius of action. In the early stages it will be so large that it is off the page, but as you descend it will represents the pilots judgment of glide range.
Extend flaps by clicking on the flap indicator - glide range will be reduced.
Try to land into the wind and near the threshold of the field (which is round) After landing the program will tell you how well you did. Strive for an excellent rating.
Being able to do this game does not guarantee a successful forced approach, but it does guarantee an understanding of the concepts involved.
There is a special version of the above simulation that instructors may find helpful to explain forced approach technique
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