When you take off, you have one goal: what ever you do, do it safely. And that means whether you abort or you lift off, it needs to be planned.

When you're flying a single or a light twin, your go/no-go decision is usually pretty simple. If an engine fails when you're still on the ground, you're aborting. Otherwise you're flying.

If you have the climb performance, you'll return for a safe landing on a runway. Otherwise you'll manage your descent and put the aircraft down somewhere safe.

But a large jet or turboprop is different. You have the power to continue the takeoff, even if an engine fails when you're on the ground.

So when do you go, and when do you abort?

Your decision's based off a V-speed: V1.

It's All About V1

V1 is the airspeed where you'll either abort the takeoff and stay on the ground, or continue the takeoff and lift off, even if you lose an engine.

V1 considers two actions: the distance it takes to abort a takeoff after an engine failure, and the distance it takes to continue the takeoff.

It's the maximum speed in the takeoff where the pilot can take the first action to abort and stop the aircraft within the "Accelerate Stop Distance". It's also the minimum speed in the takeoff where the pilot can continue the takeoff and meet the required height above the surface following an engine failure within the "Accelerate Go Distance."

It's called the "takeoff decision speed" because it makes your decision: below V1 you abort, above V1, you go. At V1, you could do either, and each airline or operator sets their own rule. But most operators go at V1. Once you hear the pilot monitoring call V1, you're going.

The reasoning behind this comes down to Accelerate Stop and Accelerate Go distances.

Accelerate Stop distance includes the total distance to accelerate from a standing start, lose the critical engine just before V1, recognize the engine failure as you hit V1, and stop the airplane using idle thrust, brakes and spoilers.

Notice reverse thrust wasn't in there?

Under FAR Part 25 , which is what the FAA uses to certify transport-category aircraft like the ERJ, you can't include reverse thrust when calculating the accelerate stop distance on a dry runway. You can include reverse thrust when calculating the accelerate stop distance on a wet runway, however.

But, even though you don't use reverse thrust for planning on a dry runway, you can use it during a failure. So, on a dry runway, you'll actually be able to stop the airplane in a shorter distance than computed when you use reverse thrust.

Accelerate Go distance is the opposite of Accelerate Stop. It's the total distance to accelerate from a standing start, lose the critical engine just before V1, recognize the failure at V1, and continue the takeoff to 35 feet above the ground at your takeoff safety speed, which is V1.

In many cases, V1 balances the field. This means that at V1, the Accelerate Stop and Accelerate Go distances are the same. But, some aircraft's performance data allow you to unbalance the field. By raising or lowering V1, the Accelerate Go and Accelerate Stop distances no longer match, but you might be able to carry more weight. And as long as you have enough runway and takeoff area to satisfy both Accelerate Stop and Accelerate Go requirements, you can depart.

There are different ways to compute V1, and it all depends on what airplane you're flying and who you're flying for. Accelerate Stop and Go distances are calculated using speed, configuration, weight, and environmental conditions. Some operators use paper charts or an FMS to calculate V1.

In an ExpressJet ERJ, the crew sends departure information to an off-site system through ACARS. The system calculates takeoff speeds, including V1, for multiple runways and configurations, and sends those speeds back to the crew, again through ACARS. Then the crew enters the speeds into the MFD.

The Normal Takeoff Sequence

The captain on our flight is the pilot flying, and the first officer is the pilot monitoring. In their briefing, they laid out their responsibilities, both for an aborted takeoff, as well as a continued takeoff at V1 or higher. With the briefing done, and after a few more checklists, we're at the runway and ready for takeoff.

When the levers hit the detent, the FADEC engine controls spool up to the takeoff power setting. The pilot monitoring confirms that the engines are at the right power setting, which on our flight is 82.4% N1. This setting changes based on the runway conditions, weight, and the environment. Most jets rarely use full thrust for takeoff: a reduced thrust takeoff saves wear and tear on the engines.

As we start to roll, the captain keeps his hand on the thrust levers.

The first officer calls 80 knots, and the captain crosschecks the speed. Both airspeed indicators match, and the takeoff continues. The entire time, the captain has his hand on the thrust levers, prepared to abort the takeoff if something goes wrong.

When the first officer calls V1, the captain takes his hand off the thrust levers, because at this point, even if we had an engine failure, we're committed to the takeoff. And today our V1 and rotation speeds are so close, they're called together.

As we're climbing, the first officer calls out "positive rate", which means we have a positive rate of climb. The captain calls for the "gear up", and we're on our way.

Handling An Engine Failure Below V1

So what happens when you lose an engine below V1?

When the engine fails before the pilot monitoring calls V1, the captain calls "Abort" and takes the controls, if they aren't the pilot flying. As the captain brings the aircraft to a stop on the runway, the first officer takes over the pilot monitoring responsibilities while the aircraft comes to a stop.

Handling An Engine Failure Above V1

What happens when you lose an engine at or above V1?

This time, since you're above V1, you're committed to the takeoff, and you continue with max thrust on the good engine. The airplane continues lifting off the ground and climbing out.

After reaching a safe speed and altitude, the crew runs their emergency checklists, communicates with ATC, and chooses where they plan to land the aircraft.

Planning For The Worst-Case Scenario

An engine failure around V1 is one of the most practiced emergencies. And, believe it or not, flying a jet like the ERJ on one engine isn't that different than flying with both engines. You climb a little slower, and you have more checklists to run, but most twin jets perform well on one engine.

It all comes down to V1: the fastest speed you can stop in your Accelerate Stop distance, and the slowest speed you can continue takeoff after an engine failure, and still make your Accelerate Go distance.

Most passengers would assume an engine failure is pretty frantic. Lots of bells and alarms, maybe some screaming. But in reality, it's the exact opposite. It's quiet, methodic, and calculated.

It's not very exciting, and that's the point. That's why it works out, ensuring you're safe whether you abort or continue the takeoff.