Weak braking on Airbus A320

[02vallancel]

Hi guys,

This is my first post on the PPRuNe forums so I hope I'm posting in the right place :)

I've spotted a few flight simulator related questions here in the past so I thought I'd add my own query!

I'm flying the Airbus X Extended package for Flight Simulator X and I'm finding the braking to be rather odd. Maybe it's a limitation of the simulation but it could be me doing something wrong :P

One time I sat in on a real A319 flight and the pilots didn't select an autobrake setting when approaching Budapest airport. When I asked why, they said that since the runway is so long they didn't need the autobrakes and used manual braking instead.

When landing my A320 in FSX I find that the foot brakes are far more effective than either of the autobrake settings, so I don't understand what the pilots meant if the autobrake performance is weaker...

So I'm curious to know the real-world difference in performance between the brake pedals and the autobrakes (both LO and MED) on the Airbus A320 series aircraft.

Thanks :-)

[dixi188]

Hi Vallance.

I can't say for the A320, but the A300 has 5 autobrake options : Off, Min, Med, Hi and Max. The Min, Med and Hi modes are looking for a particular deceleration rate. The Max setting will apply Maximum braking and is only used for Rejected take off.
If when landing on a long runway and expecting to vacate at or near the end, as in Budapest, then a pilot will probably not use autobrake but roll along the runway with ground spoilers and reverse idle until he or she judges it about right to apply the brakes to make a smooth exit from the runway without occupying it for too long. This also saves brake wear.

We once landed on 04L (about 3700m) at Copenhagen at an average landing weight with a little head wind and vacated the end of the runway at 15kts without using brakes at all. At 0400 runway occupancy time was not important.

I believe some of the latest Airbuses have a "Brake to Vacate" option so the Autobrake will apply the brakes to slow the aircraft for a designated exit.

Hope this helps.

[LetsFlyAway]

Don't expect Fsx to simulate the effects of a real aircraft the flight model in fsx is no where near correct suggest you try Xplane for a realistic flight model, it's been approved by the FAA for flight training as it's pretty close to the real thing.

[bfisk]

This is sort of general, and not type specific:

Autobrakes typically give you a given deceleration rate, and are activated shortly after touchdown.

The pro is that you get braking immideately and evenly; this is ideal on short/slippery/contaminated runways or if a specific turnoff needs to be made, or in strong crosswinds.

The con is in absorbed brake energy and thus heat - if you have a short turnaround time, heavy aircraft and limitations in use of reverse thrust (or any combination) you could very well run into a brake cooling issue.

With manual brakes, the pilot can modulate the brake pressure manually with the foot brakes, from zero to max pressure. It also allows a delayed brake application, which reduces brake heat issues.

The type of materials used in the brake units may also be of interest. On carbon brakes, wear is primarily dependent upon the number of applications rather than the force and duration of the application. The even and continous nature of autobrake may be useful here if use of wheel brakes is anticipated all the way to taxi speed and brake heat is not an issue.

Steel brakes wear primarily based on duration and force of application, so a delayed brake application (ie manual brakes) may reduce maintenance cost.

Furthermore, the economical aspect of the brake wear may vary from operator to operator. The other primary means of slowing the aircraft after landing, reverse thrust, costs fuel and engine wear. Depending on the maintenance cost structure of the brakes vs. engines (think warranty/no warranty or variable price vs fixed price for overhaul), and cost of fuel, may influence the Standard Operating Procedure regarding use of wheel brakes vs use of reverse thrust.



For any given landing, the pilots will, with due regard to safety, comfort and economy, based on their company SOPs, determine which setting will give the overall best result. (And yes...this much thought actually goes into this decision for each and every landing...but of course it gets easier with time.)