A320 family brake fan use after landing

[ulisse]

good day
I searched the forum about this subject but I did not found an answer so I open a new thread.

My understanding of the brake use on the airbus 320 is do not use brake fan until the brake are thermally equalized, so if conditions permit (no thight turn around or other constraint)I left cool down preferably without use of the fan.

I'll like to know if is reccomended to use the brake fan after landing if no special circumstances are encountered (overweight landing or heavy braking)and the brake temperature is around 250°

and again brakes temperature of 300° it's a limitations for take off only or we have to avoid this while the aircraft is parked and a long turn around is ahead?

thanks

[safelife]

Wait at least 5 minutes, to avoid oxidation.

[Denti]

We usually only use it on taxi-out. Temperatures up to around 450°C after landing usually coold down to well below 300 in the standard turnaround time, a tiny bit more if you release the brakes once the chocks are in place. If the temperature reaches 500°C or higher we should use the fan and to not stick to the minimum 5 minutes according to my company.

[Meikleour]

ulisse This topic comes up regularly. Part of the problem is that Airbus give contradictory pieces of advice in different parts of their FCOMs. The issue is whether one is concerned about brake wear or brake efficiency - and it is further complicated by the fact that there are three different suppliers of brake units to A320 and they each exhibit different qualities. Broadly speaking, carbon brakes wear less and are more efficient when they are not too cold. Google a paper by Guy Di Santo of Airbus Airlines Operations Dept. for an in depth paper on the subject. Hope this helps?

[vilas]

Brake temperature 500 degrees put it on, less than 500 wait for five minutes but if you reach turning point for the gate put it on.

[JABBARA]

An interesting phenomena: When the brake is hotter, wear less. This is well explained at
https://www.youtube.com/watch?v=SG4Aw5BujEU&t=2s

[Valmont]

From the Airbus 11th Performance and Flight Operations Support Operations Conference

4.3.3. Brake Fans (if installed)
• Taxi out
If an arc is displayed on the ECAM WHEEL page, above the brake temperature (indicating a brake temperature > 100°C), select brake fans ON. This will ensure:
- Max energy rejected takeoff will be sustained.
- The brake temperature for taxi will be in the appropriate areas, regarding brake wear, as
recommended by Messier-Bugatti and Honeywell-ALS.
• Before takeoff
If the brake fans are running, check that brake temperature is below 150°C (except ABS - see general remarks below). If temperature is above 150°C, delay takeoff until 150°C is reached with fans running, then switch them OFF.
• Taxi in
The Airbus recommendations mentioned below have been amended to reflect the advantages (claimed by all brakes manufacturers) provided by taxing with hot brakes, while also taking care of possible oxidation problems.
Brake fans selection should be delayed for a minimum of about 5 minutes or at the gate (whichever occurs first), to allow for thermal equalization and stabilization and thus avoid oxidation of brake surface hot spots.
However, when turnaround times are short, or brake temperatures are likely to exceed 500°C, use the brake fans (forget oxidation).
It should be emphasized that, the arc displayed on the ECAM WHEEL page, suggesting the selection of brake fans at taxi out, should be ignored for taxi in. Also, although displayed on the ECAM, the display of the BRAKE HOT warning after landing should not lead to the immediate selection of brake fans as long as 500°C is not likely to be reached (wait 5 minutes or gate arrival).
• Parking
Select the fans OFF, if no arc is displayed on the ECAM WHEEL page (temperature <100°C). If turnaround is short, keep the fans running down to temperatures close to ambient.
• General remarks about brake cooling fans operation
- Except for brakes manufactured by ABS (Aircraft Braking System), the temperature indicated in the
cockpit when the brake fans are running is significantly lower than the temperature indicated when the brake fans are OFF. This is because the brake fans are ventilating the brake temperature sensor that is not located inside the material itself. Therefore, as soon as the brake fans are running, the indicated brake temperature decreases almost instantaneously (except ABS). Similarly, it will take several minutes for the indicated temperature to rise, and to match the actual brake temperature, when brake fans are switched OFF.
For all brake types (except ABS), when the fans are running, the difference ranges typically from approximately 50°C at 100°C actual brake temperature up to about 150°C at 300°C actual brake temperature. As a consequence, if the BRAKE HOT warning is activated just before takeoff, the ECAM will request the selection of the brake fans, if installed, and the delay of the takeoff. When fans are selected, the warning will disappear instantaneously, but the takeoff must be delayed until the indicated temperature consistently decreases below 150°C (for a warning set at 300°C). Then, the brake fans should be switched OFF for takeoff. This is well documented in the FCOM.
- All of the indicated brake temperatures (mentioned in the above Figures 2 to 7) do not consider brake fans. Therefore, pilots should take into account the above-mentioned temperature shift, induced by brake fans operation, if targeting a brake temperature recommended for taxi.
- Brake fans should not be used during takeoff and landing roll to avoid foreign object damage to the fans and the brakes at high speed.
- If not already selected OFF, brake fans are automatically switched OFF when landing gear is retracted.
- If the BRAKE HOT warning appears after landing gear retraction, the landing gear should be extended,
if performance permits, to allow cooling in flight as requested by ECAM and published procedures. However this should not happen, if FCOM-published Standard Operating Procedures are adhered to. On A300 and A310 aircraft, brakes fans may be switched ON as they have proven to increase cooling efficiency in flight. On other Airbus types, the cooling efficiency of the fans in flight is marginal, and next FWC version will no longer require selection of brake fans in flight.

See the whole document in the attachement

[Metro man]

The brakes take longer to cool down if allowed to heat soak for a while before putting the fans on. Eg put a dish in a oven at 250' for 10 mins vs 30 mins.

[DaveReidUK]

It's not entirely clear what effect you are trying to describe.

Clearly the longer you wait before putting on the fans, the longer it will be until the brakes cool. Or is there more to it than that ?

[EmDeer]

The brakes take longer to cool down if allowed to heat soak for a while before putting the fans on. Eg put a dish in a oven at 250' for 10 mins vs 30 mins.

Interesting concept, but...

When you have a dish in the oven, you constantly put energy into it from outside. Of course it is hotter after 30 minutes, it has gotten more joules than after 10 minutes.
After last brake application the system has gotten all the energy it will get. Therefore it cannot "heat soak". It only gets thermally stabilised.

[Meikleour]

Metro man (http://www.pprune.org/members/11599-metro-man) I think you may be misinterpreting the apparent lower brake temp. due to the fans effect (ie. underreading) when they are running. The stopping energy has already been generated and it simply has to spread out in the brake pack. What is certain is that the INDICATED temp. of the brakes on the ECAM is not an accurate indication of the true heat in the brakes until a few minutes have passed.

[noflynomore]

I don't think the dish in oven analogy is a good one. There an item is merely warming up to it's surrounding ambient temperature. In brakes we must consider point-generation of intense heat in an otherwise "cold" system.
In a brake unit the heat at the point of generation (ie the disc/pad interface )is vastly above any oven temperature, I have no idea of figures but expect well over 1000'. This has to dissipate into a lot of metal and rubber and takes an appreciable time to do so, reducing on the surface as it moves deeper into the structure warming that up.. As the transfer of heat to air is proportional to Tdiff I think more energy must be transferred if the fans are used early while the surface is hotter. Sure, it won't be 1000' but it might still be 700 and so far the sensors are only seeing say 300. Wait till the sensor screeps up to 500 and the surface will be down much closer to 500 as the heat has been taken deeper into the surrounding structure. (all figures for illustration only)
How much practical effect this may have is anyone's guess.
One point to bear in mind; if you're going to use the fans try to put them on before coming on stand to avoid smothering the rampies with brake dust which they have to breathe...nano particles and all that.

[Chu Chu]

Also, if it takes time for the heat to be conducted into the interior of the structure, it will also take time for it to be conducted out of the structure after the fan cools the surface. So in theory, starting the fan earlier would not only remove heat more quickly from the still-hot surface, but also remove some of that heat before it could reach the core of the structure.

Whether any of that is significant is a different question. And, of course, starting the fan earlier will cool the brakes earlier even it the heat transfer rate is essentially the same.