View Full Version : B737 Brake Temperature assessment methods.
21st Jan 2007, 22:56
Most B737 series do not have brake temperature gauges. The only way a pilot knows the brakes are hot is during the walk-around inspection. But there are varying degrees of "hot." What method can a pilot use therefore to ascertain the brake temperature in order to minimise the risk of fusible plug blow. There are brake temperature tables but unless a thermometer is available these mean nothing. I recall a Boeing document that stated if the hand cannot be held on the brake assembly then by definition the brakes are "hot." But I am sure if that assessment method was used, few aircraft could depart on time on the short turn-around schedules used by LCC.
I suspect the Boeing "hand on brakes" method is a little vague, I would think that 50'C would feel hot to a naked hand, yet the wheels and brakes could easily get that hot in the sunshine in our hot summers (on the ramp at MEL or SYD or any city in oz).
An interesting note, I once saw a low-time-on-type F/O heat the brakes up very hot during the long taxy at BNE in an Airbus (can't recall model) the screen was showing high 400s and low 500s for all the wheels on the MLG. The Capt., kept telling him to allow the plane to build up speed and then slow the plane down with short applications of the brakes, but the F/O must have been nervous about his taxy speed because he kept those brakes dragging most of the way down that long taxy way.
I'm glad we didn't have an RTO as I suspect we might have had a little brake fade.
22nd Jan 2007, 07:59
we have temp gauges on some of the 737-300's ,and I was able to check the temp behaviour on short turn-around. I never saw it above 4,and the temp light should illuminate at 5,even when landing on short rwy's,with autobrake 3,max reverser will keep the temp in reasonable limits.
A long taxi will tend to raise the temp also,and using reverse idle will help keeping the temp down.
I've seen once smoke coming out from the brake assembly,and the temp was around 4,'hand ' test was ok. Some tech told me the brake's had just been changed..
Without temp gauges we use the tables ,and after landing on 1800m rwy's,20-25 min will be required for cooling the brakes on ground (reversers used at detent reverse thrust). In case one didn't use the reversers this time will go up to 45 min. (on the classics)
The NG (700) is a lot better _same conditions like above will give you no special procedure required on tables. Maybe that's one of the reasons we are using now mostly the NG's on short rwys.And we have one particular rwy (not only short,but also 30m wide) where the pax are always enjoying the 'carrier landings' .
So ,you see,with full reverse thrust there won't be any problem with the brakes.
Only problem we've ever had with the brakes was at a high speed RTO,followed by a long taxi to the apron resulting in fuse melt.:ugh:
22nd Jan 2007, 10:19
I recall a Boeing document that stated if the hand cannot be held on the brake assembly then by definition the brakes are "hot."
I think Boeing would be even happier if you would take the QRH, Advisory informations, Brake cooling Schedule section:ok:
Most of the time we never check that, because we often operate on long runways. I tend to have a look anyway when landing with tailwind for example and autobrake plus idle reverse. On the classics or originals it is most of the time ok within 35 to 45 minutes.
22nd Jan 2007, 12:06
I could say the maximum brake temp on a normal braking situation is around 400°C. It should always be well below this value (say around 200°) if you don't ride the brakes when not necessary. But can you feel the difference between 400° and 500° with your naked hand?
But can you feel the difference between 400° and 500° with your naked hand?
Not for very long methinks.:}
22nd Jan 2007, 12:45
Add a little bit of olive oil, and some salt and you'll feel the difference :hmm:
Anyway,the gauges are in units and 4 doesn't mean 400 ,or so I've been told.Nor does it say so in the book.I stand corrected if I'm wrong:O
22nd Jan 2007, 19:18
We only consider brake cooling time based on rejected takeoffs or high elevation landings. Otherwise we assume (perhaps incorrectly) that the brake temperatures are within limits. What is reverse idle? I've never heard the term.
23rd Jan 2007, 08:40
mullinax ,if you fly the 737,check the PI section of the qrh ( PI.22.9),at brake cooling schedule ,and you see 2 tables,one for no reverse thrust and the other one for 2 engine detent reverse thrust.This is what I called idle reverse (you could also check the reverse sys description in the FCOM 2)
23rd Jan 2007, 15:27
What is reverse idle? I've never heard the term.
it's when upon landing you avoid doing 85% N1 on reverse thrust if you have a 4000 m runway. If you read carefully approach plates you will notice that many times use of reverse thrust above idle is allowed only for safety reasons. That is because airplanes are also a bit noisy.:cool:
23rd Jan 2007, 20:01
Maybe it would be a good idea to have a brake heat measuring thermometer along with the gear pins so that the vagueness can be taken out of the brake temperature assessment. After all, light aircraft have used dipsticks for years to confirm actual fuel on board rather than rely on dipping the finger in the tank.:ok:
24th Jan 2007, 21:07
Otherwise we assume (perhaps incorrectly) that the brake temperatures are within limits..
Where ignorance is bliss, 'tis folly to be wise....