I was reading about flight RWAF9268 earlier today when a questions popped into mind. When a large commercial jet touches down, is it required to try and come to a complete stop? Or is it allowed to take off again if part of the craft fails (like the braking system, for example)? And what factors would make a pilot decide to stay one the ground, or just abort the landing?
Boldface emergency procedures are procedures that the aircrew should have committed to memory and are written in bold text. Generally speaking, the boldface for all emergencies involving brake failures, gear failures, control failures, literally anything that involves control of the aircraft after touchdown, starts with:
If fly-away airspeed available:
If fly-away airspeed unavailable:
2. Do specific airframe related items.
Emergency procedures like these will be committed to memory, and then the only problem for the aircrew to solve will be if they have enough runway remaining to get airborne again. If they don't have enough runway remaining then usually the fix to is apply emergency brakes (if the pedals hit the floor) or use backup nose wheel steering (for a steering failure) and ride it out.
Note: use of these emergency procedures doesn't necessarily indicate a failure of an aircraft system. If a sudden gust of wind at touchdown weathervanes the aircraft 45 degree off centerline, you can be sure the crew is checking for fly-away airspeed.
When a large commercial aircraft touches down, it is not committed to stopping.
However, it is committed to stopping when the thrust reversers are selected. This is because they take different time to stow and adding power while stowing would likely cause significant asymmetric thrust. And even if they don't, they take their time to stow and you are unlikely to have enough speed and runway when they finally do.
When thrust reverses are not selected, the pilots of course have to consider whether it is more likely that they can stop or lift-off again on the remaining runway. And they sometimes do choose to lift off. There are many incidents where planes went around after tail or even wing strikes or bounces as it's often easier to get the plane under control by adding power. But once thrust reversers are selected, stowing them again means loosing a lot of time and is risky, so go-around is considered out of question afterwards.
No, when an airliner touches down, it is not committed to stop.
Compared to a landing, more runway is required for a takeoff. After the touchdown, pilots have very little time to decide to take off again if they cannot stop. Fortunately1, most of the time, this decision is made very quickly. However, if an airplane is slowed down below the minimum safe go-around speed, there will (or may2) not be enough runway remaining to take off again. Therefore, pilots should accept a runway overrun, as it is probably a lesser evil.
To take off after a touchdown, there are several very important factors to consider. They include:
- Remaining runway
Probably the most important factor.
- If airplane is at or above minimum safe go-around speed, or can achieve with enough runway remaining
- Actual touchdown point
- Density altitude
- Pilot reaction time (decision time)
- Inertia of the airplane
- Time required to configuration change
1: In cases when the pilots decide to abort the landing, they decide it within the first few seconds of touchdown. I found a video of this (and this one) showing the airplane took off very quickly when aborting the landing (after the wheels touched down). Most of the time, they abort the landing before touchdown, when the gears are just a few feet off the ground (as seen here and here).
2: This depends on runway length.