In most respects a takeoff is the easiest maneuver in flying. Your instructor probably let you handle all, or at least most of the takeoff on your very first flight lesson. But the takeoff and early stages of departure continue to stand out in the accident statistics, which show only approach and landing with a higher concentration of risk.
But the takeoff is the one maneuver or phase of flight where the pilot can take all the time he needs to plan. Once in flight you can't stop or even fly too slowly while you consider how to handle a difficult situation. There is no pulling to the side of the road to think things over or to wait for conditions to improve once in flight.
And the takeoff and departure is the phase of flight that should be most predictable. We have the information available to know if the takeoff can succeed with reasonable margins. There is no need to guess before you push the throttles up.
The need for pre-takeoff planning is well understood in jets and other transport airplanes. The airplane flight manual is full of dozens, even hundreds of pages that show how the airplane will perform during takeoff under the entire range of conditions, including aircraft weight, wind, runway length, airport elevation, air temperature, runway contamination and so on.
Light airplane manuals do not provide nearly as much detail, but they do contain the information you need to know for a safe takeoff. But unlike the performance data in the jet manuals, light airplane manuals do not have performance margins included. The data in the light airplane manual accurately reflects the performance a test pilot achieved under the specified conditions, but unlike the jets, does not build in a margin to account for differences in specific airplanes, or less than perfect pilot technique.
The obvious focus of takeoff planning is what to do if the engine, or an engine, fails. We all correctly worry about engines quitting, but the facts are that in most takeoff accidents there was no power loss. The typical takeoff accident involves a failure in planning by the pilot.
The most fundamental part of the takeoff plan is to determine if there is enough runway available, and enough climb performance for the airplane to clear the terrain ahead. In the most common serious takeoff accident there just wasn't enough airplane performance available to clear the terrain or obstructions ahead. The reason this type of accident usually ends in disaster is because the pilot is faced with the choice of continuing to pull back on the elevator in the hope of climbing over the obstruction ahead, or lower the nose and fly into the trees, or hill, or whatever under control. Most of the time the human reaction is to keep pulling back and hope to make it over, which is the prescription for a stall and spin.
No amount of stall practice or spin training is going to help the pilot faced with an obstruction that his airplane lacks the performance to climb over. The solution is not to practice more slow flight, or do more stalls, but to perform an accurate and realistic pre-takeoff flight plan that keeps you out of that situation.
Many jets have a simplified takeoff planning method that covers the big majority of situations, and light airplane pilots can use the same technique. A typical simplified takeoff criteria would be that the airport elevation is less than 2,000 feet, the runway more than 5,000 feet long, no obstructions in the departure path and a clean, dry runway. Such a situation would exceed all required margins for the specific airplane so there is no need for the crew to look in the book for the exact amount of runway required or other data.
The pilot of a light airplane could make his own simplified takeoff criteria by looking in the manual and finding the required runway for an airport at 2,000 feet elevation with the airplane at maximum certified takeoff weight, no wind and air temperature at the highest you are ever likely to encounter. I would then add 50 percent to the takeoff distance listed in the manual to be comfortable. Most takeoffs by most pilots fall into this category.
But when you are at an airport that does not meet that simplified criteria much more study is required. Runway length available and the presence of obstructions are obvious issues, but airport elevation and air temperature are equally critical. A runway that is just fine on a cold day could be dangerously short on a hot one.
Many ATIS or AWOS automated weather reports will contain a message to "check density" altitude when certain conditions are exceeded. Some systems even calculate and report the density altitude. I find this to be interesting, and a welcome warning to plan carefully, but knowing the density altitude is of little use in a detailed takeoff plan. The reason is that the performance charts and graphs account for density altitude without ever requiring you to calculate it or know it. The charts show what the airplane will do from a runway at a specific elevation with a specific air temperature. Some manuals contain tabular data where you check columns of different temperatures and elevations to see required runway. But a multipart graph is more common.
A common starting point for calculating takeoff performance is air temperature. Then you follow the temperature line to airport elevation, which is really a measure of density altitude. Then you follow across the graph to your actual takeoff weight and adjust for headwind or tailwind component and read the takeoff distance on the edge of the graph. Many graphs also allow you to adjust for an obstacle height at the end of the runway or along the takeoff path.
Remember, the takeoff distance you find in the light airplane manual will not contain any margin. But you will have accounted for the critical factors of air temperature and elevation.
Actual takeoff weight is a critical factor in larger airplanes because it can vary so much. In light airplanes the ratio of useful load available to empty weight is lower so you operate closer to maximum certified takeoff weight more frequently than in a jet or large airplane. In a light airplane I just ignore actual takeoff weight and always assume the airplane is at maximum gross weight when making the plan. That just builds in extra margin for days when you are lighter than maximum certified weight.
There are at least two critical takeoff planning factors that are missing in light airplane manuals -- runway gradient and runway contamination. The charts and graphs invariably show the data was collected from a level, dry, paved surface. In transport airplanes there are correction factors for runway slope, or runways contaminated by water, snow, slush or ice. And those conditions can add hundreds and even thousands of feet to the takeoff runway distance needed.
When faced with a sloping runway and no data on how it will impact takeoff performance the light airplane pilot should always, if possible, depart downhill. Depending on the degree of slope even a little tailwind of less than 10 knots could be preferable to an uphill takeoff roll. If you must depart uphill I would add at least 50 percent, if not double, the takeoff distance you found by using the data in the manual.