Airbus Brake Problems?
 

I posted a query a few weeks back whilst observing aircraft at JNB about an A319 leaving its gear dangling for 2 minutes plus after take off.The OAT was around 30C on that day, the answers were hot brakes. Subsequent to that 10 days ago another A319 did the same thing and yesterday a TAP A340 kept his gear out for 2 minutes plus.That has happened to 3 different Airbus products in over the last 5 Sundays that I have spent spotting and yesterday the AOT was 23C.Strangely have never seen any Boeing products doing this at all.Do airbus have a weakness in that department.Any comments?

Smaller brakes plus higher approach speeds = hotter brakes.
Brake cooling fans are installed on Airbus products only.

Hi tree

i would like you to elaborate on your saying 'smaller brakes'...brakes are designed to stop an aircraft with a certain mass to stop at the end of a certain distance after landing..??? how can it be small for this certain aircraft?:confused:
i would really appreciate the thoughts

Boeing, and indeed common sense, says that you should wait until the brakes cool down before you attempt your next takeoff.

In the Bigger Busses there is an MEL procedure to follow when a Brake has beeen deactivated.
It involves leaving the gear down for a couple of minutes after take-off.
Don't know about the little Busses.

In A320 family the max brake temprature for take off (with brake fans off) is 300 degrees.
The only SOP that Airbus has on the brake fan use is after landing (five minutes or gate or 300 degrees which ever happens earlier).
In my company there is no SOP for brake fan use while taxiing out or before take off. Most captains I have flown with like to keep the temprature below 100 degrees, so as the temprature is approaching 100 degrees we turn the brake fans on. Some ex-pats I have flown with do not like to use the brake fans as much. The only time we have kept the LG down was when the brake fan was MEL and the temprature was reaching 200 degrees just before take off.

Brake Fans are a cost option on most aircraft, therefore, you may find these aircraft are not fitted with brake fans and experienced warmer brakes due to the ambient temp and a short turnaround. No drama or airbus specific problem.

As far as single-aisle comparison is required, I believe the answer is hidden under the fact that A has brake temperature indicators, thus enabling pilots to take care of their brakes, whereas B does not. If temperature for any reasons went over certain "comfort" limit, pilots are required/choose to keep the gear down. Had 737 been equipped with temp. sensors and 32S not, the thread name would be "Boeing brake problems?". Needless to say, if my assumption is correct, the operational behaviour observed really is type (manufacturer) specific.
FD.
(the un-real)

Most of the times it is not the "landing brake temp" bringing the problem, but the brake temp taxiing out.
I.e., a fairly empty Airbus taxiing behind a very slow taxiing 737 (some companies pay for blocktime!!) on a long taxiway (i.e. FRA rwy 18) involves quite a few brake actuations.
So reaching the takeoff position the brakes are reaching slowly their peak temp. Retracting the gear after takeoff, loosing the airflow, the temp is even getting higher. This requires to bring the gear down again, reduce speed with probable reconfiguratoin (slats) to observe gear overspeed limitation.
So, to avoid all the trouble, just let the gear down after takeoff for a while as a precautionary measure.
To keep the brake temp at max 100°C with help of the brake fan makes no sense from my point of view. 100°C is definitly not the optimum temperature for carbon brakes.
That´s at least what I am doing! (A-320 family)

I have never left Gear Down "because the brakes are hot"... The Airbus SOPs we work to are (as above) <300C Fans Off for Takeoff. If they are at 290C we can takeoff, and no issues that I am aware of with retracting gear as usual.
A340/A320/B757 all have procedure with brake deactivated to leave gear down for ~2 mins so wheel spins down (since automatic brake applicaiton on retraction disabled).
I trust anybody "deciding to leave the gear down after takeoff because the brakes are hot" makes the appropriate performance correction i.e. limits MTOW etc. since the climb gradient is based on gear up, whereas you have now decided to go gear down... ;)

Brake Fans are said to "halve the indicated brake temp" i.e. if brake fans are on, and the temp says 100°C, the actual brake temp is ~200°C and the temp will rise towards this if the fans are turned off, hence why the takeoff limit is 300°C Fans Off, and 150°C Fans on. So working to Fans on >100°C taxying out works well to keep well clear of the 150°C limit etc. We have the 100°C SOP taxy out, taxy in not so...
100°C is not the optimum temp as you, ~500°C is, but for brake wear purposes. The 300°C / 100°C limit is for the RTO case - a max weight / V1 RTO needs the brakes <300°C so they can absorb the energy, if the brakes are already at 500°C they may not absorb the energy required...

On the Airbus when having a wheel tachometer u/s you have to leave the gear down for a while after take off.

Someone told me that the 300c limit was not just due to energy absorption requirement with RTO, but also due to the 400c flash point of Skydrol - therefore you need below 300c to be able to retract the gear after T/O to prevent heat build up in the ldg gear bay and possible hydraulic fluid fire.

EDIT: Not flash point, but autoignition temp.. is this the stuff?

<<- SKYDROL 500B-4 FIRE RESISTANT HYDRAULIC FLUID>>

Fire and Explosion Hazard Information
=======================================================
Flash Point Method: COC
Flash Point: =160.C, 320.F
*****Autoignition Temp: =398.9C****, 750.F
Extinguishing Media: IN CASE OF FIRE, USE WATER SPRAY (FOG), FOAM, DRY
CHEMICAL, OR CARBON DIOXIDE.
Fire Fighting Procedures: FIRE IFGHTERS AND OTHERS EXPOSED TO PRODUCTS OF
COMBUSTION SHOULD WEAR SELF-CONTAINED BREATHING APPARATUS. EQUIPMENT SHOULD
BE THRORUGHLY DECONTAMINATED AFTER USE.
Unusual Fire/Explosion Hazard: PRODUCTS OF COMBUSTION INCLUDE HAZARDOUS CARBON
MONOXIDE, CARBON DIOXIDE AND OXIDES OF PHOSPHORUS.>>

tom... an interesting aspect I was not aware of. Will file away to b*lls**t my next Router Checker :)

Flight Detent: On the 737 there are temperature indicators even on the classics, not to mention the Ng's. On the Ng you'll find brake temp indicator mostly on the -800 CDS ,on the rest is not required.
The difference is in the brake assembly design, the ones on the 737 allow for a very good cooling. No fan required or ever installed on a 737.
You may land at full weight with a 737-700 on a short rwy,brake 3 ,and you'll have no cooling time required in the brake cooling schedule.
The brakes on the classics are a bit less efective, but never had a problem with them.

Incorrect. During normal take-off roll, brakes heat up at least 30°C. ECAM warning BRAKES HOT (one brake T>300°C) is ihibited from 1st engine TO power to liftoff. Once airborne, you would get
BRAKES HOT
- L/G .............. DN FOR COOL
MAX SPEED ...........250/0.6
Very good point. In fact, FCOM 3.2 under BRAKES HOT says If performance permits: and explanatory note reads: If performance permits, the leanding gear should be extended, or if already extended, it should remain so, to improve brake cooling.

I agree that "performance permitting" means "performance calculations have been revised accordingly", however if presented with the above ECAM, I think pilots would keep gear down, even if it is a twilight zone.

alexban: Our -4/500s had no indicators and from time to time you would be limited by brakes cooling schedule, albeit never longer than say 40 minutes (steel brakes type A). I understand that if equipped with temp. sensors, the cooling schedule would be probably much shorter and not limiting. The NG's are, obviously a different breed. Carbon brakes?

As mentioned by Nigel, wear optimalisation and RTO energy limits do not go along easily. To address your last point, I am afraid Airbus themselves think differently.
FCOM 3.3.10 Taxi
Brakes ..... Check
- check decceleration
- check no residual Y HYD pressure (not applicable on Enhaced's with electric brakes controls)
- check TEMP not above 100°C, if so, BRK FANS ON.

FCOM 3.3.11 Before Take-Off
This have been rewritten for clarification about a year ago. Before it said
- check temp below 300 deg,
- with fans running, check temp below 150, then fans off
which was susceptible to some lunatic explanations such as: What do you do at holding point with fans ON and 220 deg? Select fans off, find yourself below 300 and proceed with take off. :ugh: :ugh: :ugh:

Now it is clarified, however I only have the wording for fan equipped fleet:
- brake temp > 150 deg - delay takeoff
- brake temp < 150 deg - select fans off.

Note, that this "new" wording assumes the brake fans are ON once temperature rises above 100 deg, because SOPs require pilot to do so.

I wonder what is the wording for non fan aircraft, because I was taught that the 300°C limitation is "mechanical" from AFM and tied to hydraulic fluid flashpoint.

FCTM is clear: The FCOM limits brake temperature to 300 Deg C. before takeoff is started. This limit ensures that, in the case of hydraulic fluid leakage, any hydraulic fluid, that may come into contact with the brake units, will not be ignited in the wheelwell.
and fuzzy at once: This limit does not ensure that, in the case of a high energy rejected takeoff, the maximum brake energy limitation will be respected.

Happy braking...
FD
(the un-real)

Flight Detent, very busy post, too busy to read.

Exactly, how many times does this have to be covered, on the Airbus, the gear is left down to cover MEL operational procedures. :ugh: