The thrust is redirected. I don’t know how the more advanced versions work, but the simplest versions of thrust reversers are “clamshell” arrangements that close over the rear of the engines and are open at the front.
I was on a flight to Jersey in the Channel Isles when the captain announced that because of the short runway, they would use reverse thrust on landing and that would be noisier than usual, but we weren’t to worry as it was perfectly normal for landings at this airport. That indicates either that many landings are done without reverse thrust. Or certainly without as much.
I believe you are right. The spoilers are sometimes used in flight (to steepen the descent path) and almost always on touchdown, to reduce lift and increase drag. They are generally left open until the plan is down to taxi speed. (Once, landing in Hawaii, I saw them left open until we were almost to the gate – I took this to be an error by the flight crew.)
I don’t know if that would be an actual error… airplanes are quite variable, and in any case I’d rather the pilot(s) leave spoilers up or flaps down or otherwise and pay more attention to where they’re moving this large hunk of metal. Certainly, there are priorities in the cockpit, and if there’s heavy ground traffic they’re better off leaving the control surfaces alone (provided they don’t interfere with movement) until they’re somewhere (like near a gate) that doesn’t require so much of their attention. Safety first.
As I said, I just fly the small planes, but even there you can have considerable differences in how you land. The condition of the ground (grooved vs. ungrooved pavement, dry vs. wet vs. icy, pavement vs. turf), winds (light or heavy, steady or gusting), length of runway, obstacles near the field, and a dozen other factors I could name all affect how I approach, how I descend, how I touch down, and how I bring the plane to a halt.
The really big planes give a pilot even more choices.
A pilot flying a sparsely-loaded passenger plane landing on a 40 degree day may use a different technique than that exact same plane fully loaded on a 100 degree day, or at any load if there’s lots of rain or even some ice on the runway.
Man, I go fly a three-day trip and find this thread almost to page two already!
As has been pointed out before, passenger jets use a combination of reverse thrust and wheel brakes to stop. How much of each? It depends, of course!
The first thing to understand is that thrust reversers are MUCH more effective at high speeds (ie right after touchdown) than at slower speeds (ie taxi speed). After touchdown (and especially on a wet or icy runway) the airplane is in a transitional phase - shifting from flying to taxiing. The goal is to dissipate energy and bring the airplane to a stop. Immediately after touchdown, with the spoilers being deployed and the weight settling on the main gear, thrust reversers can get rid of airpseed much more effectively than wheel brakes. As the speed slows, wheel brakes become more effective. FARs for large jets use generic numbers, but assuming all forms of slowing down are used (thrust reversers, spoiler and wheel brakes) at touchdown reverse thrust and spoilers provide 90% of the deceleration. The wheel brakes provide the other 10% and continue to become more effective until at taxi speed the wheel brakes provide over 80% of the stopping power.
This is for a max-effort stop, which is an EYE-OPENER. Normally you’ll never encounter this, so the degree to which reverse thrust/wheel brakes get used depends on the length of the runway, condition of the runway, altitude of the airport, weight of the airplane, winds, and where the taxiways are located. On a cool, windy day with a long runway I’ll just use idle reverse until I get close to a taxiway and then come on the brakes. Going into La Guardia after a rainshower it’s max reverse on touchdown and immediately get on the wheel brakes.
Wheel brakes are very effective, and ABS has been around for a long time on airplanes (no cite, but at least 20 years that I know of). ABS on jets is usually only effective above a certain speed - say 15 knots or so. Below this speed you need to modulate the brakes just like in a car without ABS. But there is also a warning available to tell you that a wheel is locked or not turning. In my airplane it’s the idiot-proof “Wheel Not Turning” light, but it varies by aircraft.
One other thing about thrust reversers - they save brakes! Brakes obviously wear out and cost money to replace, so if you can use something else to slow the airplane down safely, do it.
You might see an airplane taxiing around with one thrust reverser open. This is not because they forgot: it’s a way to slow down a light airplane without burning up the brakes. Even with just one engine running, a light airplane on a downsloped taxiway can pick up a lot of speed. Rather than riding the brakes for that two-mile taxi, most people will throw open a thrust reverser and let that slow the airplane down. Nothing more than idle thrust, but it works!
Upon re-reading the above paragraph, I guess I should say that “light airplane” does not mean a single-engine GA aircraft. By “light” I mean relatively light for that particular aircraft - say 100,000lbs for an MD-80. Far below max gross weight. Light.
How about “empty” ? 
“A related question suggested by this thread: do planes have ABS? If not, why not?”
First of all, vehicles equipped with ABS have only about 60% of the braking power of similar vehicles without ABS. (cars do, anyway…I’m not sure about planes) A car with ABS just can’t stop in as short a distance as a car with ABS.
Why have ABS, then? Because most people don’t know how to drive, and for THEM, ABS is safer. For those who can brake at impending lockup, ABS is an unsafe distraction.
Fortunately, most pilots are trained & skilled at flying…I wish the same could be said of drivers. A lot is made of the fact that 50% of traffic fatalities are alcohol-related; what’s never mentioned is that 50% of the time the people involved were completely sober & still manged to get themselves into an accident. Seems to me that at least 99% of accidents should be alcohol-related.
Broomstick thanks, I KNEW there was a word that I could have used instead of “light”…empty. Hmmmm. I’ll try to work it into my vocabulary!
Flying Monk the automobile ABS question is probably worthy of another thread, but I can tell you that ABS on jets is MUCH more effective than manual braking. Modulation of the brakes is just about impossible - the brakes themselves sit anywhere from 50-150 feet behind you, and you cannot tell if they are locked up until the airplane starts sliding around. And since the brakes are actually applied by hydraulics (through an accumulator and a de-booster) the “feel” you get is entirely artificial. On an icy runway it’s entirely possible to lock the brakes up with very light pressure on the pedals - ABS is a lifesaver in these conditions.
Glad to help, pilot141. You really had me going there for minute with “light airplane” and “thrust reverser” - I couldn’t find mention of that ANYWHERE in the Cessna 150 Aerobat POH!
I do know that lear 35’s have parachutes also as a last ditch effort.
Cool! I kinda thought that this wasn’t an either-or situation.
King Friday, do you mean parachutes as a drag chute, to be deployed behind the aircraft as it’s rolling on the ground, or the large chute that lowers an entire small plane to the ground? I don’t know how big a ‘Lear 35’ is.
I work on a general aviation ramp in Baltimore, a lear jet is rather small, maybe 6 seats + 2 pilot seats. The chute is a last ditch effort to stop the plane from going off the runway, not as a means of lowering itself to the ground. Although, there are aircraft that have recovery chutes built in them. I’ve also seen the supersonic military jets (B-1, F-117) with simular chutes that are used on a regular basis. From what I understand, it’s early in development but it is available. That just may be something you see in the future on a much larger scale.
