As far as I know, a substantial part of passenger aircraft crashes are because the brakage is not as sufficient as needed (overruns runway). The reasons may be a failure of wheel brakes or aerodynamical brakes, failure of an engine or lack of fuel, what makes impossible using the reverse. Other reasons may be failures that enforce greater speed of landing approach or problems with precise steering that can cause landing too close to the middle of runway. Or if is necessary to land on a little airport, which has no sufficiently long runway. Or on the highway, which has viaducts limiting the "runway" length.
That's why I propose two emergency methods of braking.
1. In military aircrafts and in space shuttles braking parachutes are in use. Passenger aircraft could have such a parachute for emergency use. The stewardess should be able to launch it if launching from the cockpit is impossible.
2. Airplanes prepared to land on aircraft carriers have a hook which catches a rope that gives an additional braking force. This could be used during emergency landing of passenger airplanes. If we don't want to make a special hook at the bottom of the airplane, we can choose two ways:
- a rope should be located just below the nose of the airplane and catch the crus of the front wheel of the plane; the rope should be spooled on two spools, able to relieve the rope with a resistance (and convert the energy of the aircraft into heat). This is disputable whether the resistance should be fixed or automatically adjusted to situation - if anybody wants it, I will post my ideas about how to adjust it. The spools should be prepared by the airport crew either at the beginning of runway or about its middle, depending on whether there is a danger of landing near the middle of the runway. There should be several sites near the runway, where the spools could be anchored.
- as above, but the rope should be stretched above the nose of the plane. This requires a special construction of the aircraft: the vertical skeg should have a hook, or an extra hook could be exserted by the aircraft crew before the landing.