When landing a commercial airliner, there seems to be considerable variation in whether the pilot chooses to slow down to taxi speed using wheel brakes or reverse thrust. Sometimes reverse-thrust is used extensively, and on other landings I’m certain I’ve never heard the reverse-thrust being used at all.
What factors go into the decision about whether (and for how long) to use reverse thrust? Is there an economic tradeoff between fuel, brake pad material and tire tread? Is there a significant risk of FOD to the engines that dictates reverse-thrust only be used when absolutely necessary to avoid overcooking the brakes?
I don’t think I’ve ever been on a commercial jetliner where reverse thrust wasn’t used. At the speeds these planes are travelling when they land, the wheel brakes alone wouldn’t be able to do the job.
However, I will agree that small propeller driven planes rarely, if ever, use reverse thrust.
As I understand it, the calculations for allowable runway for landing must be done assuming that reverse thrust is unavailable, so presumably the brakes and spoilers must be capable of stopping the aircraft on their own.
The brakes are perfectly capable of stopping the airplane all by themselves. The contribution of reverse thrust is surprisingly small, and reversers on modern high-bypass engines are surprisingly inefficient.
Some jet airliners don’t have reverse thrust at all. As PaulParkhead notes, landing distances (and rejected take-off distances) are calculated without the use of reverse thrust. Landing distances also have a 67% safety factor added to the flight manual figures so there should be no reason why reverse thrust would be required for landing. Landing over-run accidents generally involve aircraft landing long and fast in poor weather, and in the Qantas example the auto-brakes were disabled by the misshandling of the thrust levers and this wasn’t picked up for some time by the crew.
The decision on how to slow down comes down to a combination of company policy (Qantas had a policy of not using reverse when they had their over-run), whether the landing distance available is close to the performance limit for the aeroplane, and what exit you are intending to use off the runway. Landing on runway 25 at Sydney it is very helpful to everyone if you can get off the runway before the intersection with runway 34L/16R and so you might use all of the stopping power you’ve got to achieve that. In other cases the only exit available might be at the end of the runway so you don’t use as much stopping power.
Reverse thrust and heavy brake applications make for a fairly harsh landing experience so you only use what you need to, unless the company says otherwise, in which case you do what they say.
The Airbus A380, the largest passenger aircraft in the world, was originally designed with no thrust reversers at all, just wheel brakes. Airbus ultimately decided to fit thrust reversers after all, but only on the two inboard engines.