Takeoff or Landing: Which Is the Greater Challenge?

July 6, 2005 -- -- One of the basic rules of aviation, goes an old aeronautical joke, is that you should always log as many landings as takeoffs.

Certainly it's not a hard rule to follow. Takeoffs are volitional, but landings (of one sort or another) are compulsory, and it's all too true that in 100 years of heavier-than-air flight, we've never left one up there.

Few of us, however, have been spared the cocktail or dinner party debate over which one is the more challenging. The "takeoff" crowd can cite the difficulty of accelerating and controlling a large air machine as it makes the transition from an expensive and unwieldy tricycle with wings to an airborne thing of beauty, but the "landing" advocates can cite just as much complexity and just as many historic landing accidents.

So who's right?

Well, first let's dissect both events.

Airplanes such as large jetliners on the ground are supported by landing gear (wheels). The fuselage and wings and tail flex downward slightly (you don't notice this but large aircraft structures are designed to be reasonably flexible) when on the ramp. But in the air, the wings (and to a much smaller extent the horizontal tail surfaces) support the same structure, producing enough lift (measured in pounds) to equal and then exceed the weight of the loaded airplane at rest. The transition phase we know as a "takeoff" is that process of transferring the weight from the landing gear struts to the wings, and as we all know, that's done by accelerating a big plane down a long strip of concrete (runway) until the speed gets high enough to let the plane achieve flight.

I know this is basic, but hang with me. There's a point coming.

As the plane picks up speed, the wind flows faster and faster over the wings, and yes, thanks to a thing called the Bernoulli Effect, even with the aircraft's nosewheel firmly on the runway, the shape of the wings produces what we loosely call "lift."

But until the wings are canted upward as they ram into the wind, Bernoulli's convenient equations won't produce enough upward force to lift the plane off the runway. That's why your pilots compute a certain speed for every takeoff (based on the weight of the aircraft and other factors) at which it's the best possible time to raise the nose of the plane (and thus the wings) in order to produce that breakaway surge of lift. We call that speed VR for the Velocity of Rotation, or the speed at which the pilot "rotates" the plane's nose up.

And yes, Virginia, that is a critical phase. Not dangerous, but substantially more exposed to engine problems or weather problems such as wind shear, than at most other times in the flight. But then again, this is precisely why all professional pilots are drilled constantly on how to easily handle an engine loss at the precise moment of rotation, and how to be sure the aircraft can climb out to a safe altitude no matter what single or multiple emergencies might occur.

In fact, because of all the tried and true safety margins we build in, once a jetliner leaves the runway in a normal takeoff, there is very little that can happen on the climb sequence that can't be handled routinely and safely. The exposed part of a takeoff is the time on the runway right up to, and during, rotation. If a major emergency occurs in that small stretch of time, your pilots will have to use their extensive training to make a split-second decision to fly or try to stop in the remaining runway. While it would seem that stopping would always be the prudent response to, say, a major engine failure, we also have decades of experience to tell us that high-speed aborts (accelerating to near takeoff speed and then pulling the power and stopping) have historically been substantially more dangerous than continuing the takeoff, especially when the aircraft with the emergency is heavy and moving faster than 80 knots.

But the training, skill and ability your crew has to make the right judgment in a takeoff emergency is the same skill set that enables us to lift heavy jetliners off runways by the thousands each day with no mishaps or even near-misses.

But what about landing?

Landing is actually a series of phases, the first being the "approach" in which an airplane is maneuvering at ever-lower altitude to get in a safe position from which to descend to a runway, and the final approach and landing in which the pilots are flying the aircraft onto the runway and then decelerating so that the weight transitions back from wings to landing gear.

During the approach and landing phases -- even with an engine loss (and we practice this constantly as well) -- the kinetic energy (speed) we have to build up and handle on takeoff is already present. In other words, we're already flying and already possessed of enough energy. Our biggest challenge is guiding the plane safely to the runway.

Weather is a limitation, both the type that simply won't let us see the airport until we're very close and very low, and the type that can produce dangerous downdrafts as we're slow and more vulnerable to large head and tailwind changes. Such large headwind and tailwind changes (called windshear) are a characteristic of thunderstorms, and we avoid them like the plague.

That leaves low ceiling, fog and generally duck-friendly weather, and that's where our technology really shines. Thanks to the basic aid called ILS (Instrument Landing System) which is essentially vertical and horizontal "lanes" of radio waves guiding us to the end of the runway, plus global positional satellite systems and other new methods, we can find our way to the right point over a runway with staggering precision and essentially 100 percent certainty. The procedures, by the way, are called "instrument approaches," and aviation has more than 75 years of experience constructing them. An instrument approach is a series of pathways and precise altitudes and directions on a piece of paper called an "approach plate" which, if followed carefully, will absolutely guarantee a safe approach to an airport's runway, with no chance of hitting anything on the ground.

So, which is harder? Takeoff or landing?

The only fair answer is that it's a matter of comparing apples and oranges. Both takeoff and landing phases are demanding for different reasons, but neither is inherently more so than the other.

And the great news is that both have been reduced to routine by the most successful safety system ever devised, a system that prevents catastrophes by expecting failures and training us to handle them safely.