If more throttle is applied after engaging the reverse thrust, would it shorten the braking distance?
$\begingroup$ depends on the aircraft and the engine. $\endgroup$– jwentingMay 7, 2019 at 5:24
Broadly speaking, yes.
The standard method of operating reverse thrust on jet aircraft is to use the reverser levers, which are actually thrust levers as well. As you pull the reverser levers up, you increase engine thrust. Many aircraft types will have prohibited areas between idle reverse and full reverse thrust which should be avoided (for things such as blade flutter). Importantly, reverse thrust is not considered when evaluating aircraft landing performance - it largely used to reduce wear and tear on the aircraft for reasons of economy of operation, usually idle reverse thrust is ample for this purpose. As you suggest, in an emergency full reverse thrust can be used to reduce or prevent a runway overrun.
With propeller aircraft, turbine or piston, you may enter the 'beta' mode (if equipped), creating reverse thrust and selecting appropriate engine power as desired, though as with jets, there may also be prohibited engine speeds which may be passed through on the way to a higher speed, but not left at that level.
7$\begingroup$ It's a bit of semantic nit picking, but on 747-100/200 aircraft, pulling the reverse levers up deploys the reversers. Then once they're up, pulling them back increases engine thrust. They won't come up unless the thrust levers are in the idle position and the aircraft is sensed to be on the ground. $\endgroup$– TerryMay 7, 2019 at 6:12
8$\begingroup$ Thanks Cpt Terry. Indeed, all reversers I know of won't allow the reversers up until the thrust levers are at idle and other conditions are met. This doesn't always include being on the ground, but that's uncommon. I investigated airborne reverser deployments on a type intended to prevent airborne deployment. In this type, a landing bounce could arm and initiate lift dumper deployment and the bounce of the pilot flying could also result in an un-intended reverser deployment. The combination giving a hard landing indeed, but not quite enough to bend the aeroplane in the cases I looked at. $\endgroup$ May 7, 2019 at 7:17
7$\begingroup$ @PaulSaccani Indeed "uncommanded selection of reverse thrust" is an certification issue, and this is why: en.wikipedia.org/wiki/Lauda_Air_Flight_004. (The flight crew decided a warning was "just an advisory thing" and took no action - followed by their last recorded words "Oh, the reverser's deployed") $\endgroup$ May 7, 2019 at 12:21
1$\begingroup$ It's also common just to deploy reversers on landing without adding power, just to have them available if needed, while reducing FOD risk. Some operators may discourage this because it uses up a reverser operating cycle without any brake wear and tear benefit and tell pilots to either use them or don't. $\endgroup$– John KMay 7, 2019 at 12:33
$\begingroup$ @alephzero A reverser deployed mid-flight is arguably unrecoverable. It puts so much stress on the plane and is such an anomaly that people say the simulators are not accurate. It is actually so dangerous that the FAA have mandated systems to prevent such things from happening mid-flight. $\endgroup$– NelsonMay 8, 2019 at 5:37