Thinking Your Way Through the Takeoff

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.

Contaminated runways are a complete unknown for a light airplane pilot. Snow will greatly delay acceleration and add to takeoff distance. Standing water can do the same. A wet runway -- particularly wet grass -- can have near zero coefficient of friction so stopping an aborted takeoff may be near impossible. And who can guess what a muddy sod runway will do to delay acceleration. We were all taught soft field and short field takeoff techniques, but those are just methods to make the best of a bad situation. The real takeoff distance under such conditions is just guesswork.

The other major factor to consider on every takeoff is the wind. A headwind is free airspeed and can chop hundreds of feet off the takeoff distance. A tailwind is the opposite. If the wind is fairly steady in direction and speed I would factor it into my calculation of takeoff distance. But if it is gusting and shifty I would take no credit and calculate a takeoff distance listed for calm conditions.

The manual for every reasonably recently certified airplane has a demonstrated crosswind component listed. The crosswind reported is not a limitation, but is the highest crosswind the test pilots successfully encountered during development. Most of us think the demonstrated crosswind refers to landing, not for takeoff where only the effect of a headwind or tailwind are listed. But if you think for a moment about what limits the ability of airplanes to handle a crosswind on landing you will see that most of those same factors apply to a takeoff.

The big issue on a windy takeoff is the ability to maintain directional control. It is, of course, vital that the pilot position the flight controls correctly to counter the effect of the wind. Deflecting the ailerons into the wind and avoiding an early rotation so the nosewheel maintains contact with the runway are important. But the flight controls will have little effect until airspeed builds during the roll. A strong gust from the side before the flight controls become effective can overwhelm the pilot's best efforts and weathervane the airplane into the wind.

From day one taildragger pilots learn that there is a wind limit that their airplanes can't handle safely during takeoff and they just don't attempt to depart when it's blowing too hard. A tricycle-gear airplane also has a wind limit, but unlike the taildragger, it may not become obvious until you reach that limit and control is lost. In the absence of any specific flight test data on crosswind takeoffs I would certainly delay any departure with the wind near or exceeding the demonstrated crosswind component for landing.

After you have satisfied yourself that there is enough runway for takeoff, with your own added margin, the next consideration is obstruction clearance and for that you need to know available climb gradient. Most of the time we focus on rate of climb as a measure of performance, and that is useful in most situations, but when you want to know if you can safely climb over an obstruction you need to know climb gradient.

Climb gradient is the vertical path of an airplane compared to the surface. Gradient is often expressed as a percentage that is the amount of altitude gained for every foot or mile covered over the surface. Another common gradient measure is feet of altitude gained per nautical mile over the ground.

As you can see, climb gradient involves both vertical speed and groundspeed. The slower your groundspeed for every foot of altitude gained, the steeper the gradient. That's why best angle of climb -- in other words, highest gradient -- is slower than best rate of climb. Rate of climb ignores distance covered and only compares altitude gained to the clock. But when you're trying to climb over the hill ahead the clock doesn't matter, only how quickly you are approaching the hill.

You can find climb gradient data in most airplane manuals and, like the takeoff calculation, the chart corrects for elevation, air temperature and weight. However, wind is not considered, so you should be aware that if after takeoff you turn downwind your climb gradient will be less than shown on the chart because your groundspeed will increase. This decrease in gradient with a tailwind can be very significant in light airplanes that often have quite slow best angle of climb speeds. For example, if your airplane has a Vx of 60 knots and you are climbing into a 20-knot wind, and you turn downwind with 20 knots on the tail, the actual climb gradient will decrease by about 40 percent even though the rate of climb remained at 500 fpm both up- and downwind. Remember, while climbing into the wind your gradient was steepened by the wind, but as soon as you turn downwind you lose the benefit of the headwind and have gradient subtracted from the no-wind situation by the tailwind. All pilots intuitively know that climb appears to suffer when you turn downwind, and it's a fact in terms of gradient, though not necessarily in terms of rate.

Finally your takeoff plan should include a strategy of what to do if there is a power loss. In jets and other transport-category airplanes the failure of the most critical engine at the worst possible time during the takeoff is considered in the required runway length and the ability to clear all obstructions after the failure. Every takeoff is required to be planned to continue safely after the worst possible engine failure.

Pilots of piston twins and turboprops are not required to plan for an engine failure at the worst time, but the data to do so is in the manuals. In most piston twins there is enough engine-out performance to climb away after an engine failure until you get to high-elevation airports on hot days. In that case the piston-twin pilot must understand before takeoff what the airplane will do, and if there is little performance available according to the manual, be prepared to pull the power back on the operating engine and maintain control to touchdown.

For the single-engine pilot the decision of what to do after an engine failure during takeoff is less complicated, but still must be considered before every takeoff. The basic and sound advice is to maintain minimum safe glide speed and land straight ahead if the engine quits. And that technique has proved effective many times. But the single-engine pilot who has made a detailed takeoff plan will have studied the terrain off the departure end of the runway and identified the area 20 to 30 degrees either side of the extended centerline that offers the best outcome for a forced landing. If, before takeoff, you have firmly in mind that a slight left turn, for example, will get you into a parking lot while straight ahead lies a big building, you will have already made an important decision while safely on the ground and will not be trying to sort it all out during the chaos of a sudden loss of power.

And that’s really the bottom line to takeoff planning. Consider every detail and have a firm plan of action in mind before starting the takeoff roll. It is a requirement in large airplanes and it should be standard practice in any airplane.