Hi Guy's,

 

As usual, another random question...,

 

Have been studying the QRH on my long London train journeys for the past week. All is going well except my understanding of the brake cooling schedule. Has anyone else read this section?

 

Not sure why I cant get my head around it... For example, 777F MTOW, calm winds, ISA, reject at V1.  How long do I need to cool the brakes for?

 

Also any idea why Boeing decided to use 1 to 5 for brake temps? Am missing my old Celsius readouts from Airbus. Of course that is just me nit picking, but seeing 800c on the temp readout helped me visualize a lot better. 

 

So for example, brake reading is 5, how hot is that? 500c?

 

Cheers

 

Edit - actually I do know why Boeing decided against temp readouts, the Airbus temp sensors can be inaccurate. A bit complicated to explain but due to readout being the temp of the sensor not the actual brake disk.

I believe that brake reading 5 is approximately 538 degrees celsius. Ill do some more research on the topic. Very intresting!

just as an aside

you tend to find that a new brake will be hotter than a worn unit so a numbering of 1 to 5 makes things a bit easier to figure  if there are brake problems and as you say sometimes the airbus temp sensors cause problems with actual temps

Generally engineers would not pay a lot of attention to the actual temp preferring to go with visuals and if reqd spin chks for brake serviceability,remember if it gets to hot the fuse plug in the hub will go and the tyre will deflate anyway so waiting for it to cool becomes pointless

 

rgds

Thanks for the info guy's!  Will keep looking into this, any further input would be appreciated.

 

Cheers

Let me try to help with that.

I really do not know how the airbus system works, but Boeing has two ways of looking into it.

I fly the real 737 and for a option we can have the BTMS or not. Although the 777 has the system as a default the way of reading the brake cooling schedule table can be done either way just like in the 737.

 

Without the BTMS:

 

On the first table you use the weight of the aircraft, the field temperature and altitude and the speed in which you have started the RTO.

 

That information will give you a number of reference brake energy. We now must correct that number by the event that we had. On the following page we can see that depending on the autobrake or reverse thrust we use we can make that number a little lower.

 

In the event of a RTO we do not have any type of reduction.

 

On the final table we put that reference brake energy number on the top of the table and read the following information:

 

In flight gear down - It means that, if we want to make a immediately take of we must let the gear down for a specific time to cool down. Not the best option if you consider the possibility of having another RTO.

 

Ground - means how many minutes we have to wait on the ground with the aircraft parked ( not using the parking brakes ) to cool down the brakes before a new take of attempted can be performed without any brake concerns.

 

BTMS - If we use the system we must wait from 12 to 15 minutes after the event. Read the number an apply direct to the final table and read how many minutes we must fly gear down or wait on the ground.

 

If we get a caution zone we must taxi only to vacate the runway because the brakes can melt.

If we get in thefuse plug melt zone is just a matter of time before the fuse plugs on the wheels to melt.

 

 

I've tried to give as much information as possible in the simplest way. If you guys need more information feel free to ask.

 

Best regards.

 

Moises

 

Sorry for any forum mistakes, I'm kind of new on this role forum stuff.

 

 

For example, 777F MTOW, calm winds, ISA, reject at V1.  How long do I need to cool the brakes for?

 

According to the table, that would put the corrected brake energy above 45, which indicates that the fuse plugs would melt, so no cooling required, but you will need new wheels.

FYI, the scale actually goes from 0 to 9.9, although anything over 5 is pointless because your tires will most likely be flat due to the fuse plugs melting as Bryan mentioned.

 

The scale is linear with 0 equal to >38C and 9.9 equal to 1038C.

 

Brian

Thanks, great answers everyone. Yes of course, after an RTO at MTOW in the real world you would not be concerned about cooling the brakes for the turnaround. I wanted to give a specific situation for cooling, RTO is not the best example.

 

@moises, thank you, will reread your post while looking at the QRH tables in the morning.

 

Cheers