When do pilot's decide to reject a takeoff?

I thought I'd get into a few topics surrounding my occupation. There is a lot of misinformation surrounding the aviation industry and I'd like to help clarify some of it and hope to make people more aware of what's going on behind the scenes as they travel aboard aircraft for holidays or business meetings.

In this case I'm going to talk a little bit about the takeoff roll in your standard commercial operation. Right up from the little guys, all the way up to the major airlines, these procedures are nearly identical. This procedure in particular is practiced many many times within flight simulators, and is a required item to pass successfully before you will be granted your endorsement on a new type of aircraft.

The procedure in question is the rejected takeoff, or continued takeoff after a major malfunction.

The idea is simply this, before the flight there are a lot of calculations made which are directly formed from the weight of the aircraft, temperature, density, length of runway, elevation of airport, wet, dry or snow/slush/ice covered runways etc. The main numbers that result from these calculations are what are called "V speeds". For the type of aircraft that I fly, we have a "V1" speed, a "VR" speed and a "V2" speed.

V1 Speed = go or no go speed. This is a very, very important speed which means that if any major malfunction occurs prior to this speed it is safe to abort the takeoff. The biggest example of this would be an engine failure, fire or other major catastrophic event. If any of these events occur AFTER this speed, then the aircraft (even with a failed engine) will be able to safely takeoff and you can deal with the problem in the air.

VR Speed = rotate speed. This is simple enough and is the speed at which the aircraft is rotated off the runway and very shortly thereafter becomes airborne.

V2 Speed = flight safety speed. This is a speed at which you must maintain to have absolute control over the aircraft and will allow for a safe climb out.

These are the most common numbers derived, there are some variations with different aircraft, but for the most part, this is what is calculated prior to the flight.

So for an example, I will use some numbers based on our aircraft for takeoff speeds. A typical set of speeds would be around V1=100 knots, VR=110 knots and V2=120 knots. So before each takeoff we brief to each other what we will do for our emergencies. As an example I will publish our company's standard takeoff briefing:

Pilot flying says "This will be a standard left seat, flap 15 takeoff, any emergencies prior to V1 I will call either reject or continue, if the decision is to reject I will retard the thrust levers, and apply maximum braking and reverse thrust, bringing the aircraft to a stop on the runway"
Pilot not flying then says "I will deploy the speed brakes, call 70 knots, monitor braking and reverse deployment and advise air traffic control"
Pilot flying continues with "If the malfunction occurs after V1, the only actions to be taken below 400 ft will be to raise the landing gear and reset any master/warning caution lights as applicable. Emergency return will be vectors back around to runway 34, with the minimum safety altitude of 6,700 ft. We are on the 'Stampede 3 Departure' from Calgary which is to maintain runway heading until 7,000 ft. Our speeds are V1=100 knots, VR=110 knots and V2=120 knots, do you have any questions?"

Some of that may be quite a lot of gibberish to you, but it happens before each flight so that each pilot knows what the other is doing. So if traveling down the runway on the takeoff roll and there is an engine fire in one of the engines prior to the "V1 speed" then the takeoff will be rejected. If it occurs after the speed, then it is safer to takeoff with the engine on fire, and deal with the situation in the air.

You'll be happy to know that all the major commercial airlines are able to fly very happily with only one engine, even during the takeoff. The engines can even be on fire for quite some time before a real danger presents itself.

During my training for the jet I currently fly, the instructors would tell us "if that engine fire light illuminates, take a sip of your coffee, take a deep breath, and then go through your emergency checklists." The reason being, that you don't want to rush the situation and handle it appropriately, rather than hastily doing something that could further aggravate the ordeal.

So rest assured that your flight crew is perfectly trained and capable of handling even the most dire of situations regarding your aircraft. The training is extensive and routine. Airlines do have engine failures, birds get sucked into engines, mechanical malfunctions have occured, but the airplanes and crew are well up to the challange of bringing you back to the ground safely.

I've found a couple of videos on youtube to help in my blog post. The first video is of an Airbus A330 shortly after takeoff, they encounter engine problems and have to return back to the airport. It is a quick clip but just goes to show you that the plane will not fall out of the sky.


The other video is of a Boeing 747 which has a major malfunction and rejects it's takeoff. However, they had been going very fast and possibly even past their "V1 speed" when they decided to reject the takeoff. The result was they were not able to safely stop the airplane and it skidded of the end of the runway as captured by an aiport security camera. Nobody was injured, just a banged up cargo airplane and luckily everyone walked away. It is too easy to be an "armchair quarterback" and say what these guys should have done, I would have hated to have been in their position. If they rejected the takeoff that late in the takeoff roll there was likely a damn good reason for it.


So in summary, the decisions regarding your safe takeoff and subsequent flight are figured and factored out long before you are sitting at the end of the runway ready to fly. Your crew is expertly trained and retrained to handle even the worst disaster at the worst possible time. In the simulator training the exercise is called "V1 cuts" because they will give you the malfunction immediatly before or immediatly after that V1 speed so that you can be trained to handle the emergency right at the worst possible time.

If anybody has any further questions I'd be happy to answer. Enjoy your next flight!