Figure: V1 Abort or Go, from Eddie's Notes.

Eddie Sez:

First a disclaimer: I have never had to abort between 80 knots and V1. I've aborted a handful of times below 80 knots and I've lost an engine at V1 three times. (See Flight Lessons / T-38 Engine Failure at V1, Flight Lessons / KC-135A Guam, and Flight Lessons / B-707 Engine Failure at V1.)

Now onto the subject at hand: V1.

  • Many aircraft manufacturers, Gulfstream included, call V1 "Decision Speed." The problem with that is the decision must already have been made by V1 and the action to either abort or continue the takeoff must be in progress by then.
  • The decision must have been made and you shouldn't be remaking the decision. The crew of LR-60 N999LJ violated that principle and lost the airplane and four of six occupants.
  • V1 philosophy used to stress that the thing to do was stop the airplane on the runway if you could. "Taking a broken airplane into the air is foolhardy!" they would say. Thankfully that argument is losing ground and what I am presenting here is becoming less and less personal technique and more and more accepted procedure.


[14 CFR §1.1] V1 means the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V1 also means the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance.

[14 CFR §25.107]
(a) V1 must be established in relation to VEF as follows:
(1) VEF is the calibrated airspeed at which the critical engine is assumed to fail. VEF must be selected by the applicant, but may not be less than VMCG determined under § 25.149(e).
(2) V1, in terms of calibrated airspeed, is selected by the applicant; however, V1 may not be less than VEF plus the speed gained with critical engine inoperative during the time interval between the instant at which the critical engine is failed, and the instant at which the pilot recognizes and reacts to the engine failure, as indicated by the pilot's initiation of the first action (e.g., applying brakes, reducing thrust, deploying speed brakes) to stop the airplane during accelerate-stop tests.

The manufacturer can select V1 so long as it occurs after VEF and the pilot's reaction time.

[14 CFR §25.109] Accelerate-stop distance.
(a) The accelerate-stop distance on a dry runway is the greater of the following distances:
(1) The sum of the distances necessary to—
(i) Accelerate the airplane from a standing start with all engines operating to VEF for takeoff from a dry runway;
(ii) Allow the airplane to accelerate from VEF to the highest speed reached during the rejected takeoff, assuming the critical engine fails at VEF and the pilot takes the first action to reject the takeoff at the V1 for takeoff from a dry runway; and
(iii) Come to a full stop on a dry runway from the speed reached as prescribed in paragraph (a)(1)(ii) of this section; plus
(iv) A distance equivalent to 2 seconds at the V1 for takeoff from a dry runway
(2) The sum of the distances necessary to—
(i) Accelerate the airplane from a standing start with all engines operating to the highest speed reached during the rejected takeoff, assuming the pilot takes the first action to reject the takeoff at the V1 for takeoff from a dry runway; and
(ii) With all engines still operating, come to a full stop on dry runway from the speed reached as prescribed in paragraph (a)(2)(i) of this section; plus
(iii) A distance equivalent to 2 seconds at the V1 for takeoff from a dry runway.

Regardless of what V1 the manufacturer chooses, the accelerate-stop distance will include a distance based on what would have been traversed during 2 seconds at V1 speed. That doesn't give you two extra seconds, it does give you a safety margin.

[G-450 AFM §05-01-10, ¶2] V1, TAKEOFF DECISION SPEED - the speed from which a decision to continue the takeoff results in a takeoff distance that will not exceed the available accelerate-go distance, or from which a decision and action to bring the airplane to a full stop will not exceed the accelerate-stop distance available. In the event of an engine failure, this speed takes account of the pilot recognition and reaction time of 1.0 seconds, including the pilot’s first action after recognizing the engine failure. For an all-engine rejected takeoff, this is the speed at which the pilot performs his first action to abort.

Gulfstream is telling the pilot the decision must be made in 1 second and they are allowed to certify the airplane this way since they are the ones established what speed V1 occurs at.

What it Really Means

The key phrase in 14 CFR 25 is this: "plus the speed gained with critical engine inoperative during the time interval between the instant at which the critical engine is failed, and the instant at which the pilot recognized and reacts to the engine failure." By the time you get to V1, you must have recognized and reacted to the engine failure. While Gulfstream calls V1 a "decision speed," they too note that the decision needs to be made and the action taken by V1.

In the example drawing, if it takes you a second to recognize the engine failure and move the power levers to idle, fully depress the wheel brakes, verify the ground spoilers are extended, and if your certification calls for it, deploy the thrust reversers; if all that could happen in just one second, you will have consumed 211 feet of runway before you are in the abort configuration. If you are in a balanced field condition and you make the decision at V1, you will not stop on the available runway.

First Officer Technique: call V1 so as to have the call completed at V1. Captain Technique: If you haven't heard the first syllable of the call, "Vee...", then you are in go mode.

FAA Clarification

[FAA Takeoff Safety Training Aid, pg. 2-40] The pilot flying cannot react properly to V1 unless the V1 call is made in a timely, crisp, and audible manner. One method of accomplishing this by a major U.S. carrier is their adoption of a policy of "completing the V1 callout by the time the airplane reaches V1.

The cited FAA Takeoff Safety Training Aid was published in 1993. I learned of this technique while attending the United Airlines Boeing 747 Captain's course in 1986. It seems this technique-turned-procedure came from United . . .

V1 Philosophy: Old School Method

In the days of yore – that means anything prior to 1986 for me, the days before flying “modern” aircraft – the takeoff abort briefing was short and easy to understand.

“If we have anything go wrong prior to V1 we’ll abort.”

United Airlines, 1986

I went through the United Airlines Boeing 747’s Captain’s course in 1986, just a month after they released the findings of an internal study on high-speed aborts. The study concluded that ninety percent of the high-speed aborts executed by their pilots would have been better handled in the air. Many of those aborts resulted in damage to the aircraft, serious injuries, and even fatalities.

The findings were ground breaking, challenging the mind-set of every pilot at United. The rationale, once explained, made perfect sense.

Aborting the takeoff with half the runway behind you, you are heavy, fast, you don’t have any drag devices out, the engines are spooled up, and your mind-set is “go.” In short, you are ill prepared to stop the aircraft. And the measure of “half the runway” was a pipe dream. The numbers were based on doing everything perfectly and stopping distance was supposed to be better than your initial takeoff performance. You quite often reached V1 with most of the runway behind you.

If, on the other hand, you took the airplane into the sky, if the airplane was flyable, things got better quickly. You could reduce weight by dumping fuel or simply burning it off. Then when it came down for the emergency return, the airplane could be configured with full flaps, the tires and brakes were cooler, and you would touch down with all the runway in front of you with the engines spooled back ready for reverse thrust.

United mandated a two-tiered abort philosophy: abort for just about anything at a lower speed and only for critical items above that up to V1. I saw the logic immediately and adopted their philosophy as my own. I took that with me back to my Air Force Boeing 747 squadron.

Second Thoughts About the Old School

During my Air Force Boeing 747 checkout I assumed the “you teach, I learn” method and kept the new thoughts to myself. Once checked out, I started to assert my new ideas. The pilots were receptive; the flight engineers were not. Our flight engineers all came from old school Military Airlift Command aircraft: the C-141 and the C-5. They were brought up to be integral parts of the decision process and firmly believed that if they saw the slightest hiccup from the engines they could call “Reject” at V1 minus a tenth of a knot and expect to see the pilots do just that.

After my first modified briefing from the left seat of the aircraft – “above 100 knots I will abort only for an engine failure, aircraft control issue, or fire” – the engineer objected immediately.

“If I say abort,” he declared, “and if you fail to abort, the next thing you are going to see is a crash axe.”

“Would you call abort,” I asked, “for a generator failure at V1?”

“Damned right I would,” he said, “and you better abort when I say abort. I don’t care if you are a captain and I’m just a tech sergeant.”

I agreed to do it his way, but only after insisting on an experiment. “When you call V1, how much runway do you think we are going to have left?”

“Half,” he said, reasoning that at V1 the airplane could either takeoff or abort. Of course that wasn’t true. It takes much more runway to accelerate from zero to V1 than to decelerate from V1 to zero. His error was understandable. As a pilot, my eyes were outside for every takeoff. His would be glued on the engine instruments and airspeed indicator.

“And we can stop comfortably at that point?” I asked.

“Yes,” he agreed, “but you have to apply full braking and full reverse. Immediately.”

“So with less than half the runway it is going to be an iffy stop?”

“Yeah,” he agreed, “that’s why these numbers are so important.”

“So then,” I finished, “when you call V1 today, I want you to instantly look outside and look at the next runway distance remaining marker. Memorize that and we can talk about this more once we level off.”

He agreed. Many large airplane runways have black distance remaining markers on either side. Today’s runway was just over 10,000 feet long, so on either side would be signs from “10” to “1,” counting down the distance from 10,000 down to 1,000 feet remaining. The engineer was counting on looking up and seeing the number “5” after announcing V1.

We were heavy and executed the takeoff perfectly. I knew the answer before he announced it. “Three,” he said, “and I just barely caught sight of it.”

“So,” I said, “we would have to stop an 800,000 pound airplane with the engines at takeoff thrust, the flaps at takeoff position providing very little drag, the brakes heated from a long taxi, and all of that with three or four thousand feet remaining? All that because one generator of eight goes off line?”

He agreed that maybe we would be better off flying the airplane. He took his lesson to the engineer’s union and pretty soon we were doing things the United Airlines way.

V1 Philosophy: Today’s Approved Solution

From the days of yore – circa 1985 and prior – to today, almost everyone has adopted the two-tiered abort methodology. Most brief, “I’ll abort for anything prior to ____, and above that only for an engine failure or something else we don’t want to take airborne.” The “____” was left to the aircraft type and operator’s preference. It was 100 knots in our Boeing 747 squadron but usually 80 knots everyplace else I’ve been.

“I would abort for anything”

When I started flying the Gulfstream III most briefings started, “Below 80 knots we’ll abort for anything, above 80 knots and prior to V1 we’ll abort for an engine failure or any red master warning light.”

I adopted the mantra until one day looking at the master warning panel. Back then – they’ve since changed it – the top three rows were red and one of those was for “FLIGHT REC FAIL.”

“You will abort for a failed flight recorder?”

Since then I’ve always looked at the “Abort for any red” light or message philosophy with suspicion.

Here are some red warnings in the G-450 I would not abort for in the G-450 between 80 knots and V1:

  • Aft Equipment Hot
  • Battery Hot
  • Cabin Differential - 9.94
  • Cabin Pressure Low
  • Fuel Tank Temperature

“Below ___ Knots”

In the Boeing 747 the acceleration was quick, but not so quick as to prevent some reasoned thoughts below 100 knots. You could see a system’s warning or other malfunction, process the information, and make a reasoned go/no-go decision.

The easiest was my very first takeoff in the Boeing 747. United Airlines provided an empty Boeing 747-100 for my check ride. The airplane was between flights in San Francisco and the Air Force was paying for my training and evaluation. United removed all three galleys from the airplane and we only had six people on board an airplane designed to carry more than four hundred. We were light. The takeoff trim system had three stages on warning, depending on the aircraft center of gravity. We were so light the computed trim was outside the warning envelope and even placing the switch at one extreme with the actual trim at the edge produced a warning horn at about 60 knots. I aborted. It was easy.

The Gulfstream V series, including the G-450, accelerate so quickly that it is almost impossible to make a reasoned judgment without a few basic rules. Almost everyone briefs “I’ll abort for anything below 80 knots.” I’m not so sure.

If something happens right after brake release and the airplane is doing 30 knots, you have time to glance at the Crew Alerting System and make a decision. At 80 knots on a short runway you may not be so lucky. I do brief, these days, “I’ll abort for anything below 80 knots.” It makes life easier as things get faster.

Above 80 Knots, Below V1

Above 80 knots things happen very fast in the Gulfstream world. The time between 80 knots and V1 can be just a few seconds. The list of things you are better off aborting for at these speeds is very short:

  • Engine failure, not producing thrust
  • Engine fire, still producing thrust
  • Cabin fire
  • Controllability issues, including thrust reverser deployment
  • Aircraft damage preventing controlled flight

If the failed engine is not producing thrust all of your planning assumptions become invalid. You don’t know if you can further accelerate and make it into the sky. You don’t know if you can clear the obstacle. This one is, and always has been, obvious.

If the failed engine is still producing thrust things get murkier. If it is on fire, however, the question of putting the fire out becomes controlling. Better to keep the thing on the ground and let the fire department deal with it. Their fire extinguishers are bigger than yours.

Cabin fire? The rule is if you can’t put the fire out in four minutes you probably won’t. It takes four minutes to takeoff and land in the best of circumstances. What if the cockpit fills with smoke for an unknown reason? Abort.

A deployed thrust reverser calls into question performance numbers as well as controllability. If the airplane isn’t handling right on the ground, you don’t know if it will do so in the air. Abort.

That’s it. All these years, I’ve never had to abort between 80 knots and V1.

At V1

I was at a safety symposium once when the learned speaker said, “We train our entire careers to prepare for an engine failure at V1 that never comes. Nobody I’ve ever met has had an engine failure at V1.” After his speech during a break I let him know I've had three.

The first time for me was in the T-38 at Point Mugu, see Code 7700's / T-38. The engine went from full after burner to zero thrust in an instant. A fire ball erupted from the engine forward and aft and left no doubt the thing was shelled. Fortunately the remaining engine was more than enough to limp us around the pattern.

The second time was in a KC-135A tanker in Guam, see Code 7700's / KC-135A. We went from four engines to three but the airplane was barely capable of climbing. After dumping over 100,000 pounds of fuel we made it back, albeit charred.

The third time was in a Boeing 707 at Love Field leaving heavy maintenance in Dallas, see Code 7700's / B-707. This time the engine was still producing thrust, but all the other indications were heading south.

The Mind-set

My briefing has been pretty much set since the Boeing 747 days, with a tweak here and there:

“This will be a [rated / reduced thrust] takeoff from the [left / right] seat on a [dry / wet / contaminated] runway. If we have any malfunction below 80 knots call abort, if you do, I will. Beyond 80 knots to a V1 speed of ____ knots, if we have a reduction of thrust, directional control, or a fire onboard the aircraft, or any condition where the airplane will not fly, call abort and if you do I will. Once airborne for an emergency return we [can / cannot] return here [visually / off an instrument approach]. If continuing the departure our instructions are to _____.”

Easy enough to say; hard enough to actually execute. To help things, I key off my hand positions and “swing thoughts,” much like in golf.

Below 80 knots.

At this point your left hand is on the tiller and your right hand is on the power levers. You are sprung loaded to stopping. The swing thought is: “any problem, abort.”

Between 80 knots and V1.

At this point your left hand is on the yoke and your right is still on the power levers. You are probably taking off. The swing thought is: “evaluate, abort only if you have to.” In a PlaneView cockpit, you will be sorely tempted to abort for a generator failure: screens pop and go blank, instruments get red x’d and there will be some noise. But the airplane is perfectly flyable.

Above V1.

Both of your hands are on the yoke, you are going. Swing thought: “go.”

Book Notes

Portions of this page can be found in the book Flight Lessons 1: Basic Flight, Chapter 19.


14 CFR 1, Title 14: Aeronautics and Space, Definitions and Abbreviations, Federal Aviation Administration, Department of Transportation

14 CFR 25, Title 14: Aeronautics and Space, Airworthiness Standards: Transport Category Airplanes, Federal Aviation Administration, Department of Transportation

Gulfstream G450 Airplane Flight Manual, Revision 35, April 18, 2013

FAA Takeoff Safety Training Aid, April 2, 1993