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Somewhat Stupid Question


UpperDeck

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Forgive my ignorance (please). En Route FLL>YYZ FL31000 and became aware that speed brakes were being deployed fairly frequently. I appreciate that the onboard pax saystem isn't too accurate but the indicated speed was 412 kts. Travelling SB a week earlier, with an announced tailwind, indicated speed was about 545 kts.

So---I wondered---why would speed brakes be deployed and answered myself (quietly, so as not to disturb) "ATC--flow control".

A lot of times, that voice appears to make sense. On this occasion, was I misguided?

Kicker----we noticed an unusual noise on the left side (over wing) on pushback and mentioned it to the I/C. She had heard the same noise so brought it to the attention of the Capt.

On final into YYZ---a go round due to landing gear indicator. Oops! Correlation to noise in Fll---hydraulics, maybe?

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Forgive my ignorance (please). En Route FLL>YYZ FL31000 and became aware that speed brakes were being deployed fairly frequently. I appreciate that the onboard pax saystem isn't too accurate but the indicated speed was 412 kts. Travelling SB a week earlier, with an announced tailwind, indicated speed was about 545 kts.

So---I wondered---why would speed brakes be deployed and answered myself (quietly, so as not to disturb) "ATC--flow control".

A lot of times, that voice appears to make sense. On this occasion, was I misguided?

Kicker----we noticed an unusual noise on the left side (over wing) on pushback and mentioned it to the I/C. She had heard the same noise so brought it to the attention of the Capt.

On final into YYZ---a go round due to landing gear indicator. Oops! Correlation to noise in Fll---hydraulics, maybe?

I really doubt that the speed brakes were being used in cruise, are you sure it wasn't the ailerons you saw moving? "Flow-control" would not ever be a factor for a flight from FLL-YYZ, well, actually it could be an issue if there was a significant airspace closure due to thunderstorms but even this is unlikely. The speeds you have given SB with a tailwind vs NB against a headwind are well within the expected range (don't forget that it's "downhill" when flying south so you go faster - huh.gif - that's a joke!).

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Forgive my ignorance (please). En Route FLL>YYZ FL31000 and became aware that speed brakes were being deployed fairly frequently. I appreciate that the onboard pax saystem isn't too accurate but the indicated speed was 412 kts. Travelling SB a week earlier, with an announced tailwind, indicated speed was about 545 kts.

So---I wondered---why would speed brakes be deployed and answered myself (quietly, so as not to disturb) "ATC--flow control".

A lot of times, that voice appears to make sense. On this occasion, was I misguided?

Kicker----we noticed an unusual noise on the left side (over wing) on pushback and mentioned it to the I/C. She had heard the same noise so brought it to the attention of the Capt.

On final into YYZ---a go round due to landing gear indicator. Oops! Correlation to noise in Fll---hydraulics, maybe?

The spoilers are used as "Speed brakes" and as spoilers to assist the ailerons for roll control ie turning the aircraft (and in this role would only deploy on one side at a time - which is hard to see from the cabin). Unlikely that the speed brakes would be used in cruise. The airspeed you saw would either be true airspeed or ground speed....not what the pilots read on the airspeed indicator...at that altitude they are almost always using a Mach number for speed control ie 0.80Mach. Winds can be anywhere from 180-200kt headwind to 180-200kt tailwind....so groundspeeds could range from 280kts up to 680 kts...

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Forgive my ignorance (please). En Route FLL>YYZ FL31000 and became aware that speed brakes were being deployed fairly frequently. I appreciate that the onboard pax saystem isn't too accurate but the indicated speed was 412 kts. Travelling SB a week earlier, with an announced tailwind, indicated speed was about 545 kts.

So---I wondered---why would speed brakes be deployed and answered myself (quietly, so as not to disturb) "ATC--flow control".

A lot of times, that voice appears to make sense. On this occasion, was I misguided?

Kicker----we noticed an unusual noise on the left side (over wing) on pushback and mentioned it to the I/C. She had heard the same noise so brought it to the attention of the Capt.

On final into YYZ---a go round due to landing gear indicator. Oops! Correlation to noise in Fll---hydraulics, maybe?

If one wants to slow down in cruise, one pulls back the thrust. If one pulls back the thrust too much, one starts to descend (or else wait for the aircraft to MAKE you descend :red_smile: ). Speedbrakes are used pretty much exclusively in descent to either slow down and/or increase descent rate.

I highly doubt speedbrakes were intentionally deployed in cruise to slow (normally). Not quite the area for mountain wave, but even when I'm in wave, I'd rather ride 'er into the bricks a little bit (the high speed ones that is!) rather than kill lift with speedbrakes and watch my speed window close. Or worse, let the engines spool below about 60% N1 or so... they take a LOOOOOOOOOOOONNNNNNNNNGGGGGGGGGGGGG time to come back when you are in the upper FLs, and you know what comes on the other side of the "up" in a wave... :whistling:

Granted, FL310 isn't THAT high and your margins are most likely (depending on type and weight) pretty wide, but still unorthodox to use 'em to slow that often.

My $0.02

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