737 Classic Performance

[Speedwinner]

Folks,

some of you can help me out im sure:

1. Talking about autobrakes: when we do a landing at à noise critical airport with idle reverse and autobrakes 2 a commander told me that the brakes are getting too hot for a 25 min turn around. What do you think?

2. Limited airport with obstacles in go around sector. Planning a single engine ga you are 400 kg above the weight to start the Approach. Can you compensate that with flying a faster approach Speed like 20 kt more for go around?

Thanks Folks

[Centaurus]

1. Talking about autobrakes: when we do a landing at à noise critical airport with idle reverse and autobrakes 2 a commander told me that the brakes are getting too hot for a 25 min turn around. What do you think?

The use of autobrakes is unnecessary if the runway has ample length. If you are restricted to idle reverse because of noise complaints, then depending on excess runway length available, simply allow the spoilers to do their stuff and leave manual braking until you need it. Often this will mean you can keep your feet off the brakes until slow ground speeds such as 80 knots. That should ensure cool brakes.

Many operators use autobrakes of various settings for every landing regardless of available length. That is asking for more wear and tear and hotter brakes.

[cortilla]

for autobrakes,

Look at the performance in flight section of your QRH (lots of useful stuff in there yet i have yet to see someone look at it unless on a line check).

A/C weight, pressure altitude, OAT, and expected landing speed give you a figure.

Then you use a table (next page) with autobrake setting and amount of reverse thrust used (Nil or detent).

Gives another figure.

Feed that figure into next table (below)

gives you brake cooling schedule.

I've often (actually nearly every time) using just idle reverse and even only autobrake one you exceed the brake cooling schedule for a quick turnaround. The figure i usually come up with is 43 mins or more. And remember this time only starts when you release the park brake on shut down.

Most airports that have noise issues state that the use of more than reverse idle is forbidden unless (here's my getout clause) safety factors dictate otherwise. With a wet runway or a quick turnaround safety factors override the noise issue.

Or do as centaurus states and use no brakes until below 100-80 knots.

Most of the airports i go to want me off the runway asap so that's usually the first or second high speed turn off and so i use autobrake 1 2 or 3 (seen someone use max once and boy did we stop especially as a/c was very very light).

But as always i stand to be corrected by those that have more experience than myself.

[RAT 5]

Cortilla. Interesting what you say about the brake cooling starting from brake release on stand. I used to fly for an operator where brakes were released with chocks in. Turn-rounds were not rapid; 45 - 60mins. I now fly for a rapid turn-round operator that always uses autobrakes, but reverse as well, and the SOP is brakes must always be set on stand. They say that there is no gain from releasing brakes on chocks. We operate into some short strips or short turn offs; operate on a tight schedule. I see many people use F30 but A/B 3. When asked why not F40 the answer is F30 is SOP, but we want to make a quick exit. On Carousel Airlines I wonder if brake cooling is such a hot topic. I'm not too practiced in it, and there is not enought time to delve into the charts anyway.
I've also tried to find Boeing's definition of a "quick turn-round". Unsuccessfully. Their table says that at these weights under normal 'quck turn-round' conditions etc.etc. there is no problem. Just how long are thye meaning?

[de facto]

Speedwinner,

1) I never had any hot brakes by selecting A/B 2 and idle reverse on a classic or on an NG.
The only time one brake was smoking was because of a brake change and the oil around it was heating.
The fire brigade came as we stopped refueling and the smoking side was cooler than the non smoking one.Both way within limits using ground personnel heat sensors.
I have shown to fos that landing with A/B 3 and no reverse at 25 c in barcelona did not overheat the brakes.Our landing mass was i admit quite low(about 56T).
The A/B do use quite more braking to achieve the same braking distance as they dont sense the deceleration from reversers but you would need to be real heavy in a hot day to be limited by A/B 2 and no reverse.
Best is to ask your airline for a reference weight,OAT,A/B setting for turnaround time limit.

I suggest you use your SOP guidelines for A/B usage.

2) If you are referring to a Missed Approach climb Gradient , the max weight to achieve it should be known before your flight.It is dispatch weight limitation.
However if you saved loads of fuel and end up with 400kgs overweight for the GA gradient(single engine,full thrust,flaps 15),then adding speed to your approach is not legal, you need to use a higher DA which will decrease the gradient or change runway if possible.

Hope that helps.

'Never take knowledge for granted,always check it'!!

[john_tullamarine]

(a) Planning a single engine ga you are 400 kg above the weight to start the Approach.

Weight is a certification - ie AFM - limitation. No flexibility for the pilot. Presuming you don't have an emergency requiring an immediate landing, the option is to burn down to the limiting weight for the airport. Planned landing overweight is no different, philosophically, to planned takeoff overweight ?

(b) Can you compensate that with flying a faster approach Speed like 20 kt more for go around?

You could ... if the AFM scheduled such .. which it almost certainly won't. Refer to (a).

[capt. solipsist]

Why do we actually worry about hot brakes?
Ans: To avoid fuse plug meltdown during RTO on your subsequent sector.

Anyone who has been using Brakes 1/2/3 WITHOUT reversers and hasn't had any problems has not yet done a high-speed RTO after a quick turn-around.

What about idle reverse? I haven't seen any Boeing table that factors that in, only NO REVERSE. There's a world of difference there. Are inter/extrapolations valid? That assumes values are linear. They could be exponential, though.

I agree with the other guys whose technique is to use idle reverse and let the brake energy dissipate before applying manual braking (approx 80kts). Runway permitting, of course.

Critical runway? Our prime responsibility is flight safety, so noise inconvenience can just go hang.

[Speedwinner]

Thanks for the replies!

You said you never had hot brakes on the 737. So acutally ive never been told how to learn how hot the brakes are. Or have to be. Can somebody help me out with that?

Im just wondering how boeing is planning on that: many operators have minimum gorund times. the table with the cooling schedule or the turnaround weight are hardly readable. is there a programme or a formular which makes it easier for a 737 classic? So we just ignore that fact that brakes could be hot? whats in the case of RTO? Im really not satisfied with that. My old operator used to use autobrakes every landing but with reverse. So made sense there. But my new most times we use idle reverse and AB off in normal conditions.

What is your fleet telling you and recommending?

Thanks

SW

[Pub User]

If the 'noise critical' airport also has a limiting runway, and you still have concerns after a F40 landing, then it's a safety issue and you should use full reverse.

[capt. solipsist]

The Brake Cooling Sched is not as complicated as it is tedious.

Assume for purposes of simplicity landing weight to be maximum (54.8 on most models of the 400). Simplify it even more and use 55K. That's given on the 1st column. Then assume brake application at 140Kts speed, given on the top of the chart. Check out 40 deg C to get the highest value : 29.1 millions of foot pounds on sea level.

On the next table below, Adjusted Brake Energy w/ No Reverse Thrust, round-off your 29.1 value (to simplify for purposes of discussion) to 30. Locate it on the topmost row under EVENT. You'll get a value of 19.4 for Autobrakes 1 Landing.

Moving on to the Recommended Brake Cooling Schedule (Cat A), the value 19.4 shall indicate you falling under the CAUTION ZONE.

But if you again check max brake application below 100kts, you'd end up with adjusted brake energy of 10, and min turn-around time of 19 minutes ONLY.

Simply put, if you apply brakes below 100kts even w/o reverse, you can be sure you're gonna be within the minimum turn-around time.

Having idle reverse makes it even more so.

Cheers!