Originally Posted by
NigelOnDraft
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.
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
Originally Posted by
NigelOnDraft
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.
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?
Originally Posted by Kraut
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)
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.
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)