Abort, Abort! …And How To Avoid It (Part 1)

The pilot stated that he set 10 degrees of flaps for takeoff from the relatively short runway. The ‘aircraft was slow to climb’ and once (it) was airborne, he raised the flaps. The airplane settled and collided with the ground. Additionally, the pilot said that the aural stall warning was operating throughout the attempted climbout.
–from the National Transportation Safety Board, preliminary report

Luckily neither person aboard the Beech Sport was injured, although the airplane suffered “substantial” damage when it overran the remaining runway and went through a fence, according to the NTSB. The airport in question is 470 feet above sea level, and is 2820 feet long with a listed obstacle (a pole) off the end of the airport’s Runway 32, which was favored by the wind at the time.

So far there’s no definitive answer. Was the engine developing full power (as far as we now know, it was)? Was the airplane loaded properly (there’s no reason to believe otherwise in this case)? Were adverse winds, perhaps a tailwind, a factor (winds were from 360 degrees at six knots; whether runway 14 or 32 was used was not reported). Did the airplane merely stall or “mush” into the ground (that’s the implication of the preliminary report)?

Although this particular instance provides no definitive answers to the cause of the accident, it does bring up the point of when and how to call it quits when a takeoff isn’t going as planned. And, it suggests that sometimes external factors can significantly degrade expected takeoff performance — factors we need to try to anticipate before putting it all on the line behind the yoke.

Aborting a takeoff is a matter of pilot judgment. Unless you have a realistic expectation of how your airplane will perform on takeoff, you can’t adequately judge whether your airplane is meeting takeoff expectations. To better judge the success of your takeoff attempt, you need to establish and aim for takeoff targets.

You can divide a takeoff into five phases, and for every phase set goals, or targets. Only then can you correctly determine if your takeoff is going to be successful, and if not, begin an abort while there’s still time. The phases of a takeoff are:

  1. The pre-takeoff phase
  2. The power phase
  3. The acceleration phase
  4. The rotation phase
  5. The initial climbout phase

1 — PRE-TAKEOFF: A successful takeoff begins even before you board the airplane with the intention of flight. This is when you evaluate airplane, pilot technique and environmental factors that affect takeoff performance. How much distance will your takeoff require, and how long is the available runway? Are obstacles or rising terrain on your departure path? What’s the airplane’s weight? How strong is the wind? What is the proper technique for this particular takeoff? Should you use flaps, or not? Evaluation of these questions, and those from the remaining four phases of a takeoff, needs to be made before flight, in the pre-takeoff phase.

2 — POWER: Is your airplane producing maximum available power? You won’t know unless you’ve established some power targets.

    • Do you fly a fixed-pitch propeller airplane? You should know the “static rpm” (indicated propeller speed, from the tachometer, at full throttle and with no forward motion) of the engine, and compare that to what you see at the end of the runway. Same goes for an engine equipped with a controllable-pitch propeller.
    • Does your airplane have a manifold pressure gauge? What “MP” should you see at full throttle? Most aero-engines lose about one inch of air pressure around a fully-open throttle, meaning a wide-open engine at sea level should get around 29 inches of manifold pressure (the sea level air pressure rarely varies more than half an inch above or below 30 inches).

Note: Since air pressure “lapses” at about one inch per thousand feet above sea level, that same engine in Wichita, Kansas (about 1500 feet Mean Sea Level [MSL]) would indicate about 27.5 inches (30 minus 1.5 inches for the 1500 foot elevation, minus an inch of lost efficiency in the engine). Take that airplane to Denver, CO (5000 MSL), and you’ll only see about 24 inches at full throttle.

The point? Expect what you’ll see, and verify that’s what you really get at the beginning of your takeoff roll.

  • What’s the optimum takeoff mixture? Many pilots who learn to fly at near-sea-level airports never learn what needs to be done with the “red knob” before a high altitude takeoff. Yet, as air pressure drops (see Manifold Pressure discussion above), a corresponding reduction in fuel flow is needed to result in the maximum available power. This is exaggerated by the fact that larger, fuel-injected engines tend to be set excessively rich (extra fuel flow) at the “full rich” control position, to obtain cooling required in very hot-temperature climb certification tests. Since high altitude (anything above about a 2000-foot field elevation) takeoffs in non-turbocharged airplanes by definition means less power is available, it’s even more critical that the fuel/air mixture be optimized for maximum takeoff. Check your airplane’s Pilot’s Operating Handbook (POH) for specific guidance, but in general fixed-pitch propeller engines need to be leaned for maximum propeller speed at full throttle. Those with controllable pitch propellers should be leaned per POH fuel flow tables (often placarded on the airplane’s fuel flow gauge) or for a target Exhaust Gas Temperature (EGT) setting. Regardless, know what indication you’re leaning for, and lean the mixture for that setting before beginning your takeoff roll.

3 — ACCELERATION: You’ve made your pre-takeoff calculations, and full power is available at the beginning of your takeoff roll. But are you accelerating as quickly as expected? Unfortunately, the measure of acceleration is subjective. Does it “feel” right? A better measure of acceleration is to visualize, beforehand, the point at which you expect to reach rotation speed. Pick a taxi turnoff, a “distance remaining” sign, a tree alongside the runway’s clear area, or some other feature to positively identify the spot where you should be at rotation speed. If you’re not up to that speed by reaching this rotation target, abort the takeoff. After you’ve stopped you can decide whether there’s something wrong in your technique you can correct for a second try, or if not, change the experiment — delay the trip until temperatures drop or winds are more favorable, reduce airplane weight, or otherwise modify the conditions for your next takeoff attempt.

4 — ROTATION: Reaching your rotation speed target at the predetermined distance down the runway, raise the airplane’s nose to the necessary attitude. Whether visually or on instruments, flying a Cessna 421 or an Aeronca Champ, there is one best attitude that provides optimum climb performance. Reach that attitude (Vx or, if runway distance and obstacles are absolutely no factor, a lower, Vy attitude) and the airplane will climb smartly. A few degrees more “up” and induced drag may seriously degrade climb performance; a few degrees “down” and climb rate may also be significantly eroded. On takeoff, especially when conditions require maximum performance, attitude is everything.

5 — INITIAL CLIMB: If you’ve used flaps for the takeoff, leave them set until you’ve confirmed a steady rate of climb and cleared all obstacles. “Dumping” flaps may result in a stall or altitude loss, like in the case of the Beech Sport. Don’t pull up retractable landing gear until verifying a positive rate of climb, either; many retractable gear designs suffer from a significant, climb-robbing drag increase while the landing gear system transitions from “down” to “up.” You should have a pre-takeoff idea of your expected climb attitude and vertical speed. Compare “real” to “expected” to decide if your takeoff is going as planned, or if you need to recheck attitude, configuration and power to safely transition to cruise climb.

Years ago I lectured members of a major lightplane manufacturer’s employees flying club. After the program I opened the floor to questions from the audience. One pilot asked:

My parents have a small farm airstrip in the western part of the state. When I fly there, I land at a nearby, paved airport, offload my family and luggage, then fly the airplane, lightly loaded, to my parents’ strip. When it’s time to leave I fly alone over to the paved runway, then load fuel, family and baggage for the return flight.

I’ve been using some flaps on takeoff from the farm strip, but not retracting the landing gear until well clear of the ground. I’ve been thinking that, if I made a ‘soft field’ takeoff and retracted the landing gear while still in ground effect, that the airplane would accelerate more quickly and therefore climb sooner. If I do this I might even be able to load my whole family into the airplane without having to make the side-trip to the local, paved airport.” Then he asked me, “What do you think?

I thought for a moment, then carefully observed, “It just might work. But I wouldn’t want to be the first person to try it.

All our preconceived expectations of takeoff performance come from experience and the POH. If the “book” doesn’t say the airplane can take off under the planned weight and conditions, chances are no other technique will reliably work. And, you can achieve the “book” performance only by using the “book” technique, even if you think something else will work, or some “expert” tells you otherwise. You won’t know until you try, with your own life and perhaps those of your passengers on the line. It’s simply not worth the risk.

One of the most common causations of aircraft accidents is “failure to follow standard operating procedures” — doing something contrary to the way it’s designed to work. And usually, if they survive, pilots of airplanes in this sort of mishap will tell you they “knew better than to try that.

BOTTOM LINE: Doing your homework before initiating a takeoff is your best defense against the need to abort a takeoff. Establish your takeoff targets and review your Standard Operating Procedures technique before strapping in, and consciously compare your “actual” performance to “expected” as you take the runway and during your roll. If you need luck, don’t go.

Next time: Extenuating circumstances, rules of thumb, and the takeoff abort.