The takeoff is a maneuver that's treated as a no-brainer by many pilots, but there's a whole lot more to a properly-planned takeoff than meets the eye. AVweb's Linda Pendleton discusses what pilots should think about before every takeoff, how to know if a rejected takeoff is warranted, and how to deal with takeoff emergencies if it's too late to abort.
May 22, 2000
|About the Author ...
Linda D. Pendleton is Manager
of Computer Graphics and Animation for
She is also the author of a book, Flying Jets, and scriptwriter for
several of the training videotapes published by King Schools, including
"Navigation from A to Z," "METAR/TAF Made Easy," and "Handling Emergencies."
Linda is an ATP with Citation 500 and Learjet type ratings, and a CFI with
airplane, instrument and multiengine ratings. In her 10,000+ hours of flight
experience, she's flown US Mail, freight, corporate, charter, commuter, and
served as an FAA-designated examiner for the Citation 500.
Over the years, I've had the opportunity to hang around
a lot of airports and participate in many hangar-flying sessions. (That's more
rotten coffee than you even want to think about!) One thing I never hear is a
pilot talking about going out to practice takeoffs. It's always landings. Nobody
brags about his or her takeoffs. It's always landings. Takeoffs are the
forgotten maneuver. It's just taken for granted that after the first hour or so
of dual that EVERYONE can do a takeoff and no further thought on the subject is
Well, as you may have imagined by now, it's just not quite that simple. It's
true that most takeoffs don't seem to require the fine judgment and coordination
that landings do. Also, who (besides a blimp pilot) ever heard of an emergency
takeoff? The consensus of opinion seems to be that takeoffs require little or no
planning and that just about anybody can finesse one. Almost true, but stand
behind the fence someday and watch down the runway as folks takeoff. You'll
almost always see the tail swing to the right and the wing drop even if just
momentarily before everything straightens out and "flies right!"
Maybe a little more practice is in order.
However, that's not the major failing of most pilots in regard to takeoffs.
There's a major lack of planning and a certain complacency associated with
takeoffs that isn't warranted. After all, at no subsequent point in the flight
will the airplane be heavier and using all of its available power to fly and
climb at a low speed. Yet lots of pilots simply turn onto the runway, advance
the throttle and launch into the blue. Ask most of them how much runway the
airplane used to accelerate to takeoff speed or whether the acceleration was
normal, and you'll usually be met with a blank look.
Doing It By The Book
Fig 1. Cessna 172R Takeoff Distance
(click for larger image)
Fig 2. Takeoff Speed
(Feet Per Second)
The tried and true Skyhawk is familiar to most of us, so let's see what the
book figures are for this plane. (See Figure 1.) The key to understanding and
using any aircraft performance charts is in understanding how the manufacturer
constructs them. Notice the conditions listed in the upper left corner of the
chart. They specify 10° flap; full power before brake release; a paved, level,
and dry runway; zero wind; and liftoff at 51 KIAS. Just how you do every takeoff,
right? "But," I can hear you protest, "I don't need to do short
field takeoffs, my home runway is 7,000 feet long." Nevertheless, this is
the only takeoff performance chart Cessna provides for this airplane. Since you
won't duplicate the conditions listed, the chart is useless.
The book says that for a sea-level airport at 20° C it will take 980 feet on
the ground and 1,745 feet to clear that mythical 50-foot obstacle. There are not
a lot of runways that are too short for that. Again, I hear you tell me about
your 7,000-foot runway. Well that 7,000-foot runway is one of the problems. All
that concrete in front of you tends to lull you into complacency.
Remember Palm 90? That Air Florida 737 crashed into the Potomac River. The
engine gauges erroneously gave the proper readings, yet the engines were
not putting out the anticipated power. The acceleration took longer than it
should have. (The co-pilot pointed this out several times and then capitulated to
the captain who saw no problem. The aircraft staggered into the air, stalled and
crashed.) The crew had no guidance readily available in the cockpit to judge the
acceleration much like you in the 172. That's where the 7,000-foot runway
becomes a potential problem. The 172's engine would have to be pretty sick to
not get off the runway in 7,000 feet so you are less likely to discover a
problem before you leave sweet mother earth. I think you'll agree that the time
to find out about engine problems is before departure, not 300 feet in the air
over houses. (That is NOT fun. I had it happen once, and it'll really got me
Takeoff Reality Check
So, what can we use to determine whether performance is healthy? It's a
pretty good bet that you're not going to make every takeoff with 10° flaps or
apply full throttle before brake release, so the book numbers aren't going to be
achievable. What's a pilot to do? It just so happens that you DO have an
instrument in your cockpit that will help you gauge your engine's performance
and, actually, the Palm 90 crew had it available to them, too, but apparently
nobody taught them how to use it.
That instrument is a plain old clock!
You've done this before time x speed = distance.
Also, time = distance/speed. Okay, I can just hear you saying, "Wait a
minute! That won't work because the airplane is accelerating." You're
right, but as it turns out, you can use the average speed and get close enough
for our purposes. There is one complication, however. Speed is in knots
(nautical miles per hour) and we're going to be looking for feet and seconds to
work with here. Just use this handy table. I've taken the liftoff speed in
knots, halved it to get an approximate average speed, and then converted it from
nautical miles per hour to feet per second. (For those who are interested that's
speed x 6000 = feet per hour/3600 = feet per second.)
This is inexact. (John Lowry could probably give us some exact formulas here,
but I'm just not up to calculus right now.) We're just trying to establish some
guidelines here. Of course, you know that the propeller has certain
inefficiencies that are not constant across the speed range and the acceleration
itself is not a totally straight-line function, but this will be close enough
for us to use.
Now you need to know what your ground roll should be for your takeoff. You
can do this two ways. First, you can take the ground roll given in your POH and
add a fudge factor to account for your differing technique. The other method is
to have someone note exactly where you lift off using your normal technique and
measure the distance. No matter which method you use, you're going to have to do
this for varying temperatures and altitudes to get a good idea what your
performance actually is and to set some guidelines for judging future
Let's take an example from the Cessna 172R Short Field Takeoff Distance
chart. How about a 1000' MSL airport at 10°C. The chart says the ground roll
should be 1,000 feet. Divide that 1,000 feet by the Average Speed (Feet Per
Second) listed for your liftoff speed (rounded up). That will be 51 knots for
our 172R, which we'll round up to 52 knots and use the table to obtain an
average speed of 43.3 feet per second. Divide 43.3 feet per second into 1,000
feet of ground roll and you get 23.1 seconds.
So it should take you about 23.1 seconds to accelerate to liftoff speed under
these conditions. That's a number you can find in the cockpit. You can even set
a countdown timer to measure it.
What makes this better than the numbers found in most POHs? Well, humans have
been around for a long time and we move at a normal speed of about four miles
per hour with very short bursts to about 15 mph. Our senses have a hard time
measuring anything that is faster than that and one of the things we're really
poor at is judging distance during acceleration. The only numbers you get in
POHs tell you that you should be off the ground in X number of feet. Unless
there are distance markers on the runway you're using or you are familiar with
the airport, you have no reliable way of judging the acceleration of your plane
during the takeoff roll.
If it takes you significantly longer than your calculated number to
accelerate to liftoff speed, it would be prudent to apply the brakes, taxi back
to the ramp and figure out what's going on. That's where the 7,000-foot runway
is handy it gives you space to do this without having to change brake pads
before the next takeoff. Remember, however, that the 7,000-foot runway can also
allow you to take an inordinate time to accelerate without it being apparent
because the end lights are not rushing up on you.
Plan For The Worst
So, what do you do if in spite of all your planning the engine does
start to give up the ghost off the departure end of the runway? Well, the time
to think about that was during the preflight planning before you even untied the
airplane. Pick out a place to put an airplane in an emergency and do it for
every takeoff. It's easy at your home field because you are familiar with the
geography, but the information is available for other airports, too. You can
always ask the locals where they would go in the event of an engine failure. The
perceptive ones will have some good places picked out. The place that is
probably not available to you is the runway you just departed. There has
been much discussion about the turn back to the runway, and many words written
advocating this maneuver. Make your own judgment based on your experience and
abilities, but in most cases at less than pattern altitude, it's a risky
Altitude and airspeed are your friends on initial climb after takeoff, yet
many pilots sacrifice precious knots and feet by dragging the gear for an
inordinate amount of time. What's inordinate? Anything after a positive rate of
climb is established and shows on the VSI and altimeter. I suspect the old saw
about leaving the gear hanging until there is no runway left to land on was
devised by a flight instructor who wanted to keep new retract pilots from
inadvertent gear retraction before a climb was established. Positive rate, gear
up. Eliminate the drag and increase your speed and rate of climb. If the engine
quits, the least of your problems is getting the gear back down. True, there are
times you may want to leave the gear out a little longer taxiing through snow
and slush comes to mind but as a practice, positive rate, gear up.
There are exceptions to every rule, of course. For
example, retracting the gear on a Cessna 337 Skymaster results in a huge initial
increase in drag as the gear doors open early in the retraction cycle, so the
POH advises against retracting the gear until obstacles are cleared. Know your
If all the math has made your eyes glaze over, you can judge your takeoff
performance by picking out a prominent landmark alongside the runway at a known
distance. You can use any number of things taxiways, windsocks, wind tees
every airport has something. Just pick something that is about where you should
be ready to lift off. If you aren't up to speed by then, stop. There can be any
number of reasons for sluggish acceleration and most of them are best figured
out on the ground.
To sum it all up, know how long (time or landmark) it should take you to get
to liftoff speed, clean up the airplane after liftoff to get the best
performance (and that includes keeping the wings level and the ball in the
center!) and know where you plan to go if the worst happens. You'll probably be
like most pilots and never need this planning, but if you do need it, YOU'LL