I believe this to be true (the article definitely states "Brakes are also necessary for aborting takeoffs", and V1 is the speed at which takeoff ~~occurs~~ edit: must be committed to), but this is only one instant of the journey. At other times it is certainly feasible to brake (landings included) with just the use of the thrust reversers.

> At other times it is certainly feasible to brake (landings included) with just the use of the thrust reversers.

This could be true; it's also not particularly reassuring as a passenger :-)

(Not doubting you specifically, but it'd be nice to have one of the many pilots on HN opine here. My understanding as a passenger is that commercial airliners use breaks because the margins are very narrow, especially in the presence of a tailwind or busy runway designed with breaks in mind.)

There are two distances to calculate, called accelerate-stop and accelerate-go.

Accelerate-stop is the distance needed to accelerate to V1, lose an engine instants before that, take the first action to abort at V1, and the resulting accelerate-stop is the distance between the start and end of roll. On an uncontaminated runway, this is computed without thrust reversers. On a contaminated runway, you can compute it with thrust reverser on the assumed non-failed engine(s).

Accelerate-go is the distance needed to accelerate all engines to just below V1, lose and recognize the loss, continue to Vr, rotate, climb, accelerate to V2, and reach 35 feet above the ground at V2.

When the accelerate-stop and accelerate-go are the same for the chosen V1, we call that the balanced field length.

Brakes are critically needed to achieve anything close to the book accelerate-stop distance.

There's definitely a difference between feasibility and what passengers should be guaranteed, yeah. Don't get me wrong, commercial airliners should have brakes.

I thought V1 was the decision speed, where you must takeoff unless the plane is literally incapable of leaving the ground.

Technically I think the takeoff speed is VRotate, where the plane is rotated and actually starts to leave the ground.

V1 is the “takeoff decision speed” (roughly as you describe). Vr is the speed at which rotation occurs. Vmu is the “minimum unstick” speed (the lowest speed at which liftoff is possible). V2 is the takeoff safety speed, which is faster than liftoff speed, and the minimum target speed for initial climb.

Isn’t the issue more specifically that not having brakes to abort lowers V1, which is the speed at which abort is no longer an option?