View Full Version : B737 speedbrake limitation

13th Nov 2007, 16:54
Hi guys,
is there any limitation concerning the use of speedbrake on 700? I know that there is nothing in FCTM, FCOM, AFM (except for using with flaps and versions without elevator modification).

Heard recently opinion that it makes vibrations that lead to failure of stabilizer (micro craks) and the use of speedbrake on NGs should be restricted to minimum whenever possible. To me quite strange opinion...

13th Nov 2007, 16:58
forgot to ask if speedbrakes increase load of the wing? What's your comment about using speedbrakes in light to moderate turb?

13th Nov 2007, 17:23

13th Nov 2007, 17:49
Remember to stow it!!! How Embraer can have an auto stow for their speedbrake when thrust is applied and Boeing exist in the dark ages is beyond me.

13th Nov 2007, 17:49
BTW... Is it possible to use an intermediate position between DOWN and FLIGHT DETENT in the 737? Some captains say it is, but others tell you off if you use less than FLIGHT DETENT as they say you may only use either no speedbrakes or FLIGHT DETENT, but nothing in the middle. :confused: Also some use GROUND DETENT in flight... :ugh:

13th Nov 2007, 18:54

They are talking BS.
You are allowed to use the Speedbrakes from down up to Flight-detent. However, the effectiveness of the speedbrakes is very limited indeed if not being put into flight-detent, especially from 250kts. onwards. Always be gentle with the speedbrakes, deploy and stow slowly and leave your hands on the lever at all times.

Try not to use the Speedbrakes when flaps are deployed, although not forbidden by Seattle, it is aerodynamically not recommended... better put the gear down in this case, in my opinion.

13th Nov 2007, 19:05
of course, don't forget these two more limitations:

SPEEDBRAKE not to be used beyond FLT det in flight
SPEEDBRAKE not to be used below 1000' AGL
if you see somebody violating this, it's your job to stop them...:rolleyes:

safe flying!

13th Nov 2007, 20:27
I now about that tech bulletin and that the 300kts limit doesn't apply anymore.
I was wandering if so called "good airmenship" says anything about using speedbrakes? Can I use it freely without any restrictions (except those in manuals)?

What about turbulence and speedbrakes?

The problem is that we fly with different CDRs and everyone has different way of flying THE BEST ONE (in their opinions) and if we don't follow their way of doing things then it starts to be unpleasent in the cockpit...

13th Nov 2007, 21:07
What about on the new 737-700`s though that have a 50% mark between the down and flight detent marks ? has anyone else flown with this type ?

14th Nov 2007, 00:36
Sir Donald,anyway speedbrakes should not be deployed with flaps more than 10.


14th Nov 2007, 09:37
I think Sir Donald was probably referring to his company limit which, like mine, is Flap 5 with speedbrake. Seattle's limit is Flap 10 and I've utilised this in the Sim with a medical emerg to facilitate a straight in. Speedbrake can be very usefull with Flap when coming down a slightly steep glide such as Malaga 13. It keeps the speed in check and avoids an unecessarily high throttle position that deploying the gear would lead to. Snag is if you go from Flap 5 to Flap 15 and gear and forget to stow the brake you'll bust the limit and have some paperwork to file. Obviously if its not enough then drop the gear. Some guy's just don't like using brake with flap so will always use the gear. Nothing wrong with that and at least it avoids the trap above albeit its not very fuel or noise efficient.

Using the speedbrake at high speeds will put more stress on the airframe but if your in a moded aircraft there is no longer any restriction on it. If you plan ahead wisely you should be able to avoid the need for it. If its required then use it but it should be the exception at high speed not the norm.

Those who say its either down or at the flight detent are correct as the aircraft employs differential spoilers any intermediate positions can cause rapid roll rates. I think boeing document that as well.

14th Nov 2007, 10:16
Just as an aside, the Malaga ILS is not particularly steep at 3.2 and the problem comes because it apppears to be bent by the ridges on the approach. The best way around this is, in my experience, to fly V/S until 7 DME when you are clear of the ridges, follow the altitude minina on the plate and ignore the GP until then.

Coupling to the GP can produce descent rates of up to 1800fpm inside 10 miles.

14th Nov 2007, 18:35
V/S has its risks too !

14th Nov 2007, 20:52
I don't even like using, or seeing used, speedbrakes with Flap 5. You start feeling a horrible vibration through the airframe, and I hate to think what it is doing to the flaps! At that speed the effect of the brakes is very limited, so I agree it is better to mkae judicious use of early gear rather than hang on brakes. As for coming down the AGP GS with brakes out, not me at all! Flap 10 gives you more drag if you want it. Brakes just shake you.

glad rag
14th Nov 2007, 21:03
Once again a interesting and informative "tech" thread.

14th Nov 2007, 22:42
Your right Rainboe flap 10 does work well as its at the same mvr speed as flap 5 and fully deploys the LEDs and no gear warning horn either and I quite often use it. However if you have to maintain 180 kts for ATC or the procedure then its not a viable option for a good deal of the approach as your useing flap as drag which is frowned on by the company and in my view is poor airmanship.

Personaly I'm quite happy to use brake and flap, often you find you need it just to keep the speed under control or to get it moving backwards then your able to stow it again. Dropping the gear will work but once its down you tend not to bring it back up so in a-lot of cases that will mean dragging it in for a stretch burning more fuel and making more noise. Certainly not wrong to do so. Cats skins etc

15th Nov 2007, 11:17
I think its best used as a "switch", either on or off "flight detent" or "stowed". If yr below 220 kts I'd suggest configuring with flaps and or gear if you really need the drag, I can't think of a valid reason to use S/B in this regime, F1 gives buggerall drag and below 190 kts the worlds your oyster with flap.