Is there a Max speed to deploy the speed brakes? Searching the limitations section of the 747-8 FCOM I couldn't find one.

Nope.

 

There isn’t one but I did find an article on the b738 that mentions the limit that was introduced when a flight crew noticed horizontal stabilizer vibration when they deployed the speed brakes at 325 knots. So the FAA limited the max speed to 300knots.

1 minute ago, ph-cxz said:

There isn’t one but I did find an article on the b738 that mentions the limit that was introduced when a flight crew noticed horizontal stabilizer vibration when they deployed the speed brakes at 325 knots. So the FAA limited the max speed to 300knots.

Reference for that? Thanks.

5 minutes ago, downscc said:

Reference for that? Thanks.

While pretty old and probably solved with later aircraft of the b737 series. It does how that there is a risk when using speed brakes at higher speeds.

AD 2001-12-51

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/AOCADSearch/0FF43E2A8F0C938F86256CC900702D1C?OpenDocument 

Thanks, agree... I found an entry in the B737 FCOM Limitations section on pg L.10.9.  Do not operated airplane in speeds in excess of 300 KIAS with speedbrakes extended.  WARNING: Use of speedbrakes in excess of 320 KIAS could... damage the horizontal stabilizer.

However, this thread is asking specifically about the B747-8.  The only limitation noted is that use of speedbrakes in flight with flaps past 20 is not recommended.

Thanks all. Actually I was wondering about the NG as well.Just stay well below the bricks and I guess you'll be fine.

Yeah no limit on the 744 or 748, just expect some vibration if you put them all the way up at higher speeds.

The LCF’s can vibrate quite heavily with full speedbrakes, but to my knowledge there isn’t a limit on those either.... not that you ever need them anyway with all the extra drag. 

4 hours ago, Jetlinker said:

Yeah no limit on the 744 or 748, just expect some vibration if you put them all the way up at higher speeds.

This statement is not quite correct, I'm sorry to say!  On the 744 you can only select Speedbrake in the air as far as the Flight Detent and the panels will tend to blow back at higher speeds and so become slightly less effective.  However, application of Speedbrake in flight on the 744 is definitely NOT approved with Flaps 25 or 30 (you will get an EICAS message if you do), or below 800ft AAL.  Operationally, their use is also not permitted (i.e. DO NOT USE) with any Flap setting greater than Flaps10 in order to preserve the life of the Flap beams.  Although there are no speed restrictions as such, these particular Boeing limitations are contained in the B744 Flight Manual under 'Flight Controls'.

Looking at this issue in practical terms, ideally you should aim to use the Speedbrake sparsely and then only when you are clean in order to slow down and/or increase the rate of descent for a given speed.  If you find yourself needing to use Speedbrake when you already have the Flaps extended - and presumably with the aircraft already well into the descent and going relatively slowly - then you might also need to think about what could be going wrong with your descent calculations and the approach path.  Instead of ending up high and fast which will almost inevitably result in a rushed approach, it is usually far more sensible to enter a Holding pattern, or extend the distance to touchdown, or extend the gear, or (depending on your position from the airfield and the amount of height you need to lose) discontinue the approach and give yourself more time.  Then, when you are at a safe height with the aircraft under proper control again you can ask ATC for another attempt at the approach.

Edited January 22, 20197 yr by berts

Should’ve been more specific I guess. I meant no speed limit, since that was what the OP was about. 

Edited January 23, 20197 yr by Jetlinker