737-800 RTO Brake Question

[pp763]

I was on a FR 737 on friday 13th jan incidently and on the takeoff roll we aborted quite far into it and as it was 24L at EGCC the autobrakes were disarmed after around 3 seconds of severe braking and we rolled to the end as there are no taxiways down the far end.
We returned to the holding point and waited twenty minutes for brake cooling. Anyway the question is, as we braked to come to a stop at the holding point we shook quite violently, the brakes were released and then applied again and we came to a holt again shaking. Is this because the brakes were hot?
When we got to Dublin They felt fine as usual. Also as we aborted did I see white smoke coming from the brakes or was I imagining it?
Many thanks.

[jonny dangerous]

I was on a FR 737 on friday 13th jan incidently and on the takeoff roll we aborted quite far into it and as it was 24L at EGCC the autobrakes were disarmed after around 3 seconds of severe braking and we rolled to the end as there are no taxiways down the far end.
We returned to the holding point and waited twenty minutes for brake cooling. Anyway the question is, as we braked to come to a stop at the holding point we shook quite violently, the brakes were released and then applied again and we came to a holt again shaking. Is this because the brakes were hot?
When we got to Dublin They felt fine as usual. Also as we aborted did I see white smoke coming from the brakes or was I imagining it?
Many thanks.


Yes. And probably no, you weren't imagining it. There is a small possibility the shuddering was due to the Captain's legs and feet shaking from the adrenaline also.:)

[john_tullamarine]

Haven't been involved with the 800 but possibly anti-skid operation ?

[Old Smokey]

The B737-800 (amongst others) has Auto-Brake, which applies maximum braking in the event of a Rejected Takeoff, and Anti-Skid is a normal component of Auto-Brake and Manual braking.

Most aircraft have a speed threshold below which Anti-Skid does not operate, and this is no different on the B737-800. Below this speed, there is no Anti-Skid, and brake locking CAN occur when Maximum braking is applied, leading to considerable juddering. The Auto-Brakes are disengaged by momentarily applying normal manual braking, whereafter modulated manual braking without Anti-Skid can take place. This seems to fit your sequence of events -

"as we braked to come to a stop at the holding point we shook quite violently" - Yes, 'as we came to a stop', i.e. at lower speeds, maximum braking is still being applied without Anti-Skid, some wheel locking / skidding is a distinct posibility.

"the brakes were released and then applied again" - The pilot has depressed the manual brakes, temporarily releasing the Auto-Brake, and then commenced Manual braking.

"and we came to a holt again shaking" - The pilot is now applying manual braking, and modulating it to prevent skidding / wheel locks.

Actually, your description is a pretty accurate depiction of a typical RTO from high speed.

BTW, the reason for the low speed threshold below which the Anti-Skid does not work is to prevent a very undesirable and unwanted 'Anti-Skid commanded' brake release during taxy and ground manoeuvering operations.

Regards,

Old Smokey

[HON 1R]

Just out of curiosity, what caused the RTO?

Thanks.

[jonny dangerous]

Smokey, according to the original post, the aircraft taxied to the "holding point" at which it came to a stop shuddering...I would think this is indeed do to the hot brakes, and not modulating brake pressure to avoid lock.

I've flown the 320 with the Carbon Brakes, and the NG with the steel, and can say that the steel brakes on the Boeing definitely will shudder at even relatively low speeds when brake pressure is applied after they've been heated up.

[Shaka Zulu]

Our NG's are equipped with carbon brakes. Don't know if FR has got carbon brakes ticked on the options list at Boeing or not though

[pp763]

Thanks everyone for the replies, however when I referred to the shuddering as we stopped. It started at no more than around 10kts until something like 5kts when he released them and then again down to 0kts. The shuddering didn't happen on the runway as we performed the RTO.
In response to G-DALE's question I visited the flightdeck in Dublin and the Captain just said it was a light that came on.
They were off to Reus in less than half an hour after that so I don't think any engineering presence was needed in Dublin.

[HON 1R]

In response to G-DALE's question I visited the flightdeck in Dublin and the Captain just said it was a light that came on.
Thanks, it's just that I hadn't heard anything about the incident.

Dale

[Alan Partridge!]

FR have steel brakes. Gone for the cheaper option unsurprisingly. Seem to do a good job to me.

[Flughaven]

Appearently steal breaks do not heat up as quick as the carbon breaks. Hence the quick turnarounds in high temps in summer. Method behind the madness perhaps?

[supercarb]

Our NG's are equipped with carbon brakes.

Really? Does Boeing know about this?

[Shaka Zulu]

Uh ofcourse Boeing does. It's been ticked on the option list before they were made I presume. We're not the only airline with carbon brakes on the NG's either.

Carbon brakes can be kept for more cycles and so keep cost down for replacing them since they fade less quick than steel brakes. (if the correct braking technique is applied).

(thread creep) back to the original thread....: never experienced a shudder like that on our NG's, only when the antiskid activates as Old Smokey said before. Interesting one

[supercarb]

That's interesting. Up to now my understanding was that only steel brakes are available for the B737NG. Who are your brakes made by?
Update: Boeing announced yesterday that carbon brakes are being developed for 737NG and will be introduced in 2008. So I don't see how the brakes you have today could be carbon ones.
http://www.boeing.com/news/releases/2006/q1/060130a_nr.html

[breagh01]

I'm an engineer and work on NG. we have carbon brakes too. just for no particularly interesting point they are A LOT easier to change too as usually it takes 3 guys to lift a steel pack without the lift and even then we struggle. (gonna go eat some weetabix i think:\ ).

[Dehavillanddriver]

Supercarb, I am with you I was certainly told that carbon brakes were NOT an option on the NG.

I had a look at the standard options catalogue back a few years ago and didn't see them there then.

[breagh01]

ok, guess we should all stand corrected, just checked with Boeing and also see Fli/Int mag page 7 for article relating to this. funny though 5 of us here thought it was carbon. so we are ashamed and await the cane with trousers down (don't get carried away). (skulks off with tail between legs :O )

[OverRun]

breagh01
No skulk off needed nor tail between legs - this is Tech Log where we share experiences and thoughts and learn from the process. Sometimes we get it right first off and sometimes we get to learn more about it. Thanks for your input. Couple of things (1) am I now right in reading that the NGs don’t have carbon brakes yet? (2) since engineers are experienced and clever people, if they thought that the brakes were carbon then is it that carbon brakes are that close to steel in appearance?
BTW if you want to know how carbon brakes really work (don’t use the PPRUNE search engine because it dies earlier than 2006, go to: http://www.geocities.com/profemery/aviation/carbon_brakes.html

[Hedncld]

Have you been on an MD-80 - shuddering is a way of life for us. I haven't been able to figure it out yet. Some claim 'hot brakes' but I have seen it shake pretty bad on the first flight of the day. I think it is related to the steel brakes but I have no facts to support that.
Take care
hednclds

[CaptainSandL]

Current 737NG brakes are made from a steel alloy called “Cerametalix(R) friction brake material”. The name gives the clue that they are trying to be ceramic/carbon like in their performance and they are much improved from early steel brake technology.

I suspect that Boeing have only started offering these a) because of IGW variants especially the -900ER & b) because Airbus have them and they don’t want to appear inferior.