Speed Brake Usage on B737 Classic and NG

[POOKEY]

I have been told that when flying the B737 Classic to use full speed brake ( do not use intermediate positions ) ! Can anyone enlighten me on this and is it applicable to the B737 NG also ?

[Wizofoz]

I don't see why you would want to use anything but full speed brake on any type. If you are in a high energy situation (too high and/or too fast), an application of full brake until on profile then putting them away is more efficient than a partial deployment for a longer time.

The NG speed-brake is slightly more effective than the classic IMHO (I've only flown 700s in the NG series), but still not great. The biggest tip I can give is to use it early, and use it at high speed. If high and fast, keep the speed up and use the brake to increase ROD, THEN slow down, as it creates more effective drag fast than slow.

[buttline]

I concur wholeheartedly with WizofOz - when you're looking to get down and slowdown, in the 73 it seems to work much better if you get down first, then slow down. The SB is definately more effective at high speed. I also can't see the point of intermediate SB positions.

It's best to sort it out early if you're high. However, sometimes you are held high by ATC closeish to the field where some thought is needed. Asking for extra track miles is probably the most sensible. However, cranking the speed right up to 320kts with full SB will give you very high rates of descent (especially if you are ACCELERATING to 320 i.e. slow down if you are held high - just like VNAV PATH does). However, if you think it's gonna be tight (we've all been there) consider limiting the speed to 270 so you can take the gear early - haven't investigated scientifically but, IMHO, I reckon SB + Gear at 270kts is a steeper descent gradient than SB only at 320 kts. Obviously this kind of thing should not be routine but a 'get of jail card'.

Having a couple of mental 'gates' in mind helps. Eg at 20miles you would normally expect to be at 250kts and 6000ft AAL. If you're at 4000ft AAL, you can afford to keep high speed and you won't need speedbrake to slowdown is one I find helpful. After all, SB is a grubby tool isn't it?

[CaptainSandL]

I agree with the descent planning advice of Wizofoz. You either need speedbrake or you don’t, the intermediate position will only give you all of the noise for little of the drag and twice the roll rate…

The answer is in the FCTM page 4.18. (31 Oct 2003). Descent – Speedbrakes
“Use of speedbrakes between the down detent and flight detent can result in rapid roll rates and should normally be avoided.”

S & L

[alexban]

I agree with CptSandL ,this is what the book says.The problem with the SB on the 737 it's that they can produce some strong vibrations at full flight detent position.These vibrations will be greatly reduced with the SB just bellow flight detent.
On the NG this was a problem from the beginig ,causing some LCO,at speeds greater than 300kts.They did some modifications on the stabiliser,and this restriction was lifted,but we still have a warning in the FCOM ,not to use the SB at speeds greater than 320 kts on the NG.
Indeed,the 737 has very good aerodinamics,and sometimes flyes like a glider,the speed refusing to go down.It is easier to reduce speed during level flight,especially with a tail wind.
The NG it's even more slippery than the Classic.
I use speed no more than 300 kt during descent,this will give less vibrations at flight detent SB,if not required otherwise by the atc.Also the turbulance speed for the 737 is 280 kts,easier and comfy to go there from 300 than from 320 kts.
Brgds Alex

[4MONU]

Between Up and FLT detent, there are no gradients or indents, to show amount of spoiler deflection desired. (unlike in the bus - think they have numbers?)
The flight spoiler accuator's are programed for a certain deflection to FLT detent. Now the Spoiler mixer is calibrated / Certified only AT THIS certain delection. Anything between is in the area of 'un-calibrated / un-certified'.

Try it - Initiating, or coming out of a turn, i.e. During aeleiron deflection, extending or retracting speedbrakes (passing slowly in-between the detents) will lead to a little dance of the control wheel. Now IF we had a mixer with a little shoddy rigging ?

The Auto-pilot roll rates are also calibrated / certified only at FLT detent and UP.

CaptainSandL has passed on the right 'advise from manufacturer' bit.

Cheers.