Quick braking question for jet drivers

Comhrá

Quick question about braking after landing:

After touchdown in say, a B737 or A320 or bigger, are brakes applied immediately upon touchdown, or are thrust reversers and spoilers used to decelerate to a certain speed before applying brakes? Just something I'm curious about.

Negative_G

Comhra wrote: »

Quick question about braking after landing:

After touchdown in say, a B737 or A320 or bigger, are brakes applied immediately upon touchdown, or are thrust reversers and spoilers used to decelerate to a certain speed before applying brakes? Just something I'm curious about.

Brakes are used as soon as the main landing gear is down. Brakes, unsurprisingly, contribute the most to the deceleration of an aircraft.

Spoilers lose their effectiveness as the aircraft slows down due to the decreasing air flow. It varies by operator but many will have a cut off point in the roll out where TR's are stowed or only used at idle as the risk of FOD increases as the aircraft slows.

Spoilers will deploy automatically once the weight on wheel/squat switches are activated and enter ground mode.

Similarly, thrust reversers can be activated once the weight on wheels/squat switches are in ground mode. Some auto stow after reaching a certain speed, others are retracted manually after landing.

Generally, there is no requirement for the nose wheel to be down before activating either the spoilers and thrust reversers, provided the main gear have touched down.

If you have a significantly long runway, the crew may elect to not use max braking and allow the aircraft to roll to the end or a convienent exit if it is safe and practical. In any event, the crew would ensure the brakes are working and slow the aircraft to a safe speed and continue the roll out.

There may of course be some different rules on different aircraft but the above is very common.

Comhrá

Thanks Negative_G, great explanation - exactly the info I was looking for!

John_Mc

It's also worth noting that all Jets (that I know of anyway) have an autobrake system which will automatically apply the brakes to give you a consistent braking distance and for improved safety. Airbus use Low, Medium, Max and Boeing use 1, 2, 3, Max.

Pilots will use this and then disable it by applying brakes themselves when they're at the speed they want to be at

Lustrum

Some more info for you - my current type we have autobrakes, however all our landing performance is calculated with only manual braking and ground spoilers being taken into account. Same goes for our thrust reversers.

My previous type which was also a jet had no autobrakes nor reversers, we had to open the windows and put our hands out to slow down :-)

bkehoe

Negative_G wrote: »

If you have a significantly long runway, the crew may elect to not use max braking and allow the aircraft to roll to the end or a convienent exit if it is safe and practical. In any event, the crew would ensure the brakes are working and slow the aircraft to a safe speed and continue the roll out.

'Brake to vacate' and minimum runway occupancy time are standard in most airline operations now as well as consideration to the noise impact, therefore often idle reverse thrust when possible (mandatory in some airports like CPH and others usually at night, eg BCN/MAD). Therefore we calculate our desired braking so as to reach a safe speed approaching the exit we're planning to take (around 30-45kts for a high speed exit).

Worth pointing out that most aircraft types 'Autobrake' systems command braking based on a deceleration rate. At lower Autobrake settings this deceleration rate is usually achieved aerodynamically on dry/wet runways at higher speeds and therefore the wheel brakes only start being required at lower speeds. This is very noticeable on the 737 with autobrake 1 or 2.

martinsvi

Lustrum wrote: »

My previous type which was also a jet had no autobrakes nor reversers, we had to open the windows and put our hands out to slow down :-)

BAe 146/RJ?