Vanity can play a part, and sometimes, reversers are just not necessary. Landing on a 11 or 12 thousand foot runway, with an exit planned at the end means if you use the reversers and don't disarm the autobrake, ATC may require you to exit the runway since you'll be at a walking pace half-way down the runway and thus potentially obstructing traffic behind you.

Or, if you land on the north runways in Vancouver (YVR), noise abatement requires minimal use of reverse, regardless of time of day.

The third option is that they didn't work on that particular aircraft on that particular flight. Thrust reversers are generally not required to stop the aircraft, and performance charts often do not consider the stopping power that reversers provide in their calculations. Just reversers may provide "bonus" stopping power. So if the reversers don't work for some reason, the aircraft can still be dispatched safely.

Gail is right though too, TRs save brakes. Autobrakes target a specific speed reduction in feet per second per second, so if the reversers are providing speed reduction, the brakes will not need to work as hard.

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