The fusible plugs in the A320 family melt around 900C and this is the temp at which maintenance action is required anyway. I've never seen them above 500!

Cheers,
mcdhu

I seem to remember that fuse plugs come in three different colours that melt at 3 design temps. Can't be bothered to look up the temperatures but anyone thinking of touching a brake unit to see how hot it is should not be allowed near an aircraft..

Slick,

To the best of my knowledge Boeing test useing half worn cold brakes

Totally depends on when the aircraft was certified, the present FAR's (25.109) states A flight test demonstration of the maximum brake kinetic energyaccelerate-stop distance must be conducted with not more than 10 percent of the allowable brake wear range remaining on each of the airplane wheel
brakes. However, that only applies to aircraft certified post 1998.

Mutt.

To get back to the original question, I have no idea how hot (or not) a brake should be in normal (or abnormal) use - I am not privy to that information. A brake unit at 200C is too hot to touch, as is one at 500C.

Unless you have a brake temperature monitoring system and some sort of guidance, go into the QRH with the prevailing conditions and the landing wt. (max if you don't have it) and see what it says about cooling times.

One of the things to check for if you don't have a monitor system is that that braking energy has been spread fairly equally between units. If one is smoking and another is cold, you have a problem.

Some manufacturers recommend leaving the gear extended for a few minutes after takeoff in certain situations to ensure adequate cooling; obviously not after a heavy V1 cut but it seems to be accepted practice on a 'short turnaround'.

On the Boeing Customer 1 (C1) flight, you will demonstrate that the plane you are about to buy RTO's correctly. Normally from 100-110 kts depending on the Boeing test pilot. Doing my first C1 with a real nice old boy (30 yrs in test flight) I asked him if I should leave the parking brake OFF after taxi in having rejected at Boeing Field at 110kts, new brakes (steel CAT C) smoking like mad. 'Boy, there's no energy in those brakes.' Is what he said. LWT was around 50 tons, 15 tons below MLWT. That was a nice calibration ride, the fuse plugs were miles away from going, but perhaps the next RTO, 20 mins later, Field Length Limited would be exciting!

Jambo B. Interesting comment by your Boeing test pilot in which he implies that a 110 knot abort at 50 tonnes is a low energy event and nothing to worry about.

He is right, of course. But it makes me wonder why Boeing select 80 knots as the upper limit speed for an abort based purely on a Master caution light appearing, when clearly a higher speed such as 100 knots might be equally as safe.

It has always concerned me that a engine overheat light appearing during the take off run at (say) 100 knots and well below V1 of any sort, is not a valid reason to abort - yet it is if it occurs below 80 knots.

An engine overheat light can also precede a fire warning and I think it would surely be prudent, if faced with an engine overheat, to consider aborting it it came on say 20 knots below V1. It is just that 80 knots seems rather low in view of the Boeing test pilot's remark on low energy?

I understand that some B737 operators use 100 knots as the upper limit for an abort based on a Master Caution light alert. I think the A320 uses 100 knots, too?

Or is it possible that Boeing decided to kill two birds with one stone as it were, by having the normal 80 knot airspeed check as the dividing line for a Master Cautions go/stop? As usual, Boeing don't give reasons - it lets you fight it out among personal opinions. Fat lot of good that is.

First of all, in answering Milt's question on the 'blow-out' plugs, I'm guessing you meant the fuse plugs installed on the wheel rims. Fuse plugs prevent excessive tire pressure built up after excessive braking and during RTOs and as such have nothing to do with the temperature of the brake pack.

Second, aircraft with turnaround times of 30 mins or less would usually have brake-cooling fans installed. Brake-cooling fans are customer-specific items as such you won't find them on aircraft flying long-haul routes.

How hot are hot brakes? Dunno, but I bet PIA do!

A most dedicated Aircraft Engineer died,
as a result of an explosion of a B737 tyre, soon after arriving on stand, at Lagos International airport, in 1979.
May He Rest In Peace.

Unrelated to this event, every proper operator of jet aircraft worldwide now use nitrogen rather than compressed air to charge their aircraft tyres.

r304ndy, the fuse plugs are activated by temperature not pressure. After a high energy RTO the heat from the brake soaks into the wheel structure. Above a certain temperature level, the tensile strength of the wheel material starts to decrease. Eventually the wheel strength will degrade to the point where it can no longer contain the tyre pressure, at which point structural failure of the wheel occurs. To avoid such a failure the fuse plugs are set to release the tyre pressure before the wheel temperature reaches the critical level.

Interesting question and one that leads to other areas of " Professionalism ", IMHO.
How hot is a brake ? What "resources" do you as a pilot or engineer have available to you in order to determine this ? Are there brake temp gauges installed ? Is there a digital thermometer available from your engineering organisation ? Can you see smoke ? If there is smoke, is there an accompanying odour ? Does the brake appear to be new ( colour of the carrier nice and fresh plus a ton of pedal fodder on the wear pin ) ? New brakes tend to " burn off " the build fluid which is a synthetic lube. Also, minor hydraulic fluid leakage will smoke off with a quite characteristic odour.
The suggestion to touch a brake has been, I would suggest, taken a little too literally. During a walkaround by either a ground engineer, F/E or Pilot if I did not see them hold their hand slightly above the brake, I would think that they are failing to use the resources available to them. It stands to reason that the closer you can put your hand, the cooler the brake. Experience will tell you if it is hot, or HOT !!! ( remember if it is suspected or confirmed to be HOT, there is a right and a wrong way to approach or exit the vicinity of that wheel )
This leads to the 2 most overlooked and undervalued resources I know of. Common sense and experience - and I don't just mean your own. What of the other resources available to you ? How many of you have built a relatonship of trust with some of your engineers or pilots that is built on mutual respect and acceptance of individual experience and demonstrated capacity ?
I stand to be flamed but if there are not situations where the word of a trusted partner in aviation cannot be taken at face value then we have come so far only to end up nowhere. A wise man will always evaluate the souce of his information and that should in many, but certainly not all lead to an acceptance that an " it's fine " reply from your ground engineer really is just that - nothing to worry about. To think that an " it's fine " is just an excuse to shirk work is an undervaluation of a fellow professional, in many cases. ( I would never assert that it's always true though ). His experience will have hopefully taught him that 30-45 minutes cooling on a widebody Airbus brake at around 375-400 indicated is actually no problem. Are you taught that releasing carbon brakes serves no purpose ? Check with your ground engineer. He may well have learned through experience that releasing them actually DOES speed up cooling. Consider the variables - what is the OAT ? Is there a cooling breeze ? Does the pack outlet impinge on the undercarriages ? How much time do I have ? is it a long taxy to the departure point ? Is it a busy period at the airport ? Would I expect a long hold ? Granted you may not always have the best resources available, so, err on the side of caution. Use cooling fans - whatever you have available to satisfy yourself that you can reach the FCOM/OPS manual limits
.
It's a wandering post, I know but if you can't smell a bird injestion before you see evidence of it, then you are not using all the resources available to you.

Back in the dark ages of jet aviation we used a pyrometer to check brake temps on short turns. It worked well on the old iron brakes instaled on the DC-8-63 and the 747-100. The -200 had brake temp indicatiors installed.

The Boeing AFM had a brake cooling statement and a chart that could be used to calculate minimum brake cooling time based on aircraft landing weight and the OAT. Landing at 635,000 at 0 dges C gave something close to 1+30 minimum ground time. We were scheduled for a 0+45 turn. We never made it and took delays on almost every flight until I stumbled into that statement in the AFM.

Pilot technique is a large factor. A lead footed pilot can get more heat in the brakes than the pilot that lets it roll using minimum braking force.

My standard trick was to walkaround the aircraft as I blocked it in and look at the brakes. If the arrival was before sun up, if they were glowing, I had my answer. If there were shimmers of heat raising between the gear, I had my answer. If they didn't give any indication of being hot, I would hold my hand over the inboard disk and feel for heat. If the temperature didn't get my attention, I would lightly touch the brake piston housing. If I could hold my hand on the brake housing we were good to go. This information was in a Boeing Airliner on more than one occasion dating from the mid 1970's.

Don

Fuse Plugs and Hot Brakes.

This thread has shown that there are a few potentially dangerous myths and misunderstandings floating around concerning aircraft brakes and their limitations in being able to transform enormous amounts of kinetic energy into thermal energy and then dissipate that thermal/heat energy over time.

As stated earlier - ignore the energy already stored in overly hot brake packs, then follow with an aborted take off and I hope you can walk away from the heap off the end.

How many know the XXX millions of ft pnds of energy absorption capability designed into YOUR brakes.?
How many know the melt temperature of YOUR fuse plugs or even whether they are in your wheels.?

Please someone who knows give us a typical listing for a few heavies.

Here is one medium heavy out of the memory bank. F-111 brakes at 15 degrees C are designed to absorb 147 million ft pnds.

But it gets to be a bit complicated if you need to interpolate for a higher temperature start point than 15 degrees C. To enable these calculations you need to know the maximum design end temperature. The modern carbon disk brake pack apparently starts to go pear shaped around 1,000 degrees C

Knowing the numbers gives you the key to calculating how much you have left with brake pack temperatures above 15 C.

As an ageing TP, I seem to recall a figure of around 300,000,000+ ft pnds for a Valiant having 4 brake packs. Did an AUW full braking stop employing the old maxaret antiskid from a ground speed calculated to prove the design specs. Blew two tyres near the end of the roll out as two wheels locked up. Much smoke for 15 minutes or so as firecrew gingerly applied dry powder fire suppressant. Later examination of the disassembled brake units showed the extreme distress of most components. The disks were thick copper heavily chromium plated. Don't remember the peak temperatures reached but around 800 degrees would be a good guess..

Accelerate-stop testing is known by TPs to be extremely hazardous.

I guess most of it been covered here but a couple of comments.
Yes fuse plugs protect the tyre from busting in the event from high temperatures that generate hi pressures. These plugs just melt under hi temp and release the air pressure. Temp varies from aircraft to aircraft and wheel depending on the max tyre pressures.
Wheels that have blown fuse plugs just have a detailed inspection and crack check and new plugs installed.
Am surprised about the guy getting killed as the plugs hould have gone before then:confused:

Initially production certification was done for the RTO with new brakes. In fact it was normally practice to install brand new brakes for that particular test. The DC 10 overrun after RTO when it should have stopped in time ( NYC I think) caused a rethink and subseqent tests were done with worn brake PLUS an AD was issued that reduced allowable in service brake wear limits.

One point that has been missed is that the hi wheel temps do not only from from the brakes.
The normal flexing of the tyres during taxying at hi-weights is also a very good heat generator.
During some tyre problem we had with Dunlop tyres, Dunlop sent people out to investigate and they monitored tyre temperature on turnarounds with a temp probe that gave instant readings.
They also showed us a film of a V bomber ( Valiant I think) that was just towed up and down a runway at max weight with no braking and they tyre temps went off the clock! ;)

Don`t worry about brake temp.....
 

Just turn the brake fun on....;)