787WannabePilot

After my real world flight, I don't feel so bad about using my speed brakes for extended periods of time

23 posts in this topic

Flew down to Florida  few days ago. Flying the 737 I have been taking note of how the pilot(s) fly on take off and landing.

I guess the winds flying into Fort Myers on Monday were pretty strong, as the pilot had the speed brakes extended on descent for a good 4 minutes +,  and even with flaps 5 (or 10?) on approach still having them extended out. First time we used RWY 10 in all the years I have been coming down here. 

In the sim, I find some flights I have been extended the speed brakes for quite some time as well. Kind of neat to see it done on a real flight.

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I was on a Swiss 330 and they left the spoilers halfway up during almost the whole decent. They finally retracted them on the last right turn capturing the LOC for RW 14.. 

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The line pilots that visit here have commented that they use speedbrakes about half the time.  Much depends on the traffic, if there is no one ahead of you ATC isn't going to care if your speed slips upward... there is usually lots of distance once you are down to let things slow down.  However, in busy airspace everyone needs to be on the same IAS to give the controller a chance at maintaining desired separation.  This will usually result in speedbrakes.

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Well, as a real 330 pilot I can assure that is a real hard plane to slow down during descent. Don,t know about the 737 but with the 320 we used the speedbrakes many many times during descent and app. 

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Speed brakes are used on almost every flight.  They are a flight control and are there to be used.  Sim pilots seem to have this obsession that having to use the speed brakes is akin to admitting you have made some type of error in your flying.

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3 hours ago, downscc said:

The line pilots that visit here have commented that they use speedbrakes about half the time.  Much depends on the traffic, if there is no one ahead of you ATC isn't going to care if your speed slips upward... there is usually lots of distance once you are down to let things slow down.  However, in busy airspace everyone needs to be on the same IAS to give the controller a chance at maintaining desired separation.  This will usually result in speedbrakes.

It wasn't the use of speedbrakes that I found interesting, it was the extended period of time. 

1 hour ago, JoeDiamond said:

Speed brakes are used on almost every flight.  They are a flight control and are there to be used.  Sim pilots seem to have this obsession that having to use the speed brakes is akin to admitting you have made some type of error in your flying.

Very true, and something I was guilty of as well. 

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As an aside, surely an aircraft which doesn't want to slow down as though it's hit a wall when power is reduced & in a descent is a Good Thing? It demonstrates efficient aerodynamics... 

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6 hours ago, JoeDiamond said:

Speed brakes are used on almost every flight.  They are a flight control and are there to be used.  Sim pilots seem to have this obsession that having to use the speed brakes is akin to admitting you have made some type of error in your flying.

Anchorage-based Captains I used to fly with called it the “Lever of Shame.” Of course they’re a different breed and they all learned to fly on the 737-200 which is also a different breed. 

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22 minutes ago, Spin737 said:

Anchorage-based Captains I used to fly with called it the “Lever of Shame.” Of course they’re a different breed and they all learned to fly on the 737-200 which is also a different breed. 

I dunno why, but that made me chuckle. 

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23 minutes ago, Spin737 said:

Anchorage-based Captains I used to fly with called it the “Lever of Shame.” Of course they’re a different breed and they all learned to fly on the 737-200 which is also a different breed. 

In that case I’d use them every descent just to annoy them. :)

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2 minutes ago, 787WannabePilot said:

I dunno why, but that made me chuckle. 

I have visions of Septa Unella in the Jumpseat with a bell shouting “SHAME”

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8 hours ago, JoeDiamond said:

Speed brakes are used on almost every flight.  They are a flight control and are there to be used. 

Sure - and I think this might be a bit of a US/EU thing to a certain extent as I know you guys over there have some pretty aggressive STAR descent profiles and slam-dunk ATC demands which are unachievable without extra drag.

Fundamentally, however, it is a question of smoothness and efficiency. Is it more efficient to turn the heating in your house on full whack, wait until you're dripping with sweat and then open all the windows to quickly cool it down, or to turn the heater on less and/or anticipate turning it off earlier so that you don't overheat and have to then throw all that energy away? 

As I say, I'm not disputing that the speedbrakes are there to be used if necessary -- if the question is is it better to end up high and fast on approach and go around/end up off the end of the runway or use some speedbrake and get the energy level of the aircraft under control then clearly it needs using (and generally earlier rather than later!). But in a sim with little in the way of ATC restrictions and minimal traffic levels, you can usually start down any time you want. There is no energy problem that couldn't have been solved by closing the thrust levers and starting down earlier, no matter how slippery the airframe! I know a friend who flies corporate jets (and has done for a very long time) often comments on the amount of speedbrake use when he positions on airline flights and appreciates the occasions when there isn't so much...

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7 hours ago, HighBypass said:

As an aside, surely an aircraft which doesn't want to slow down as though it's hit a wall when power is reduced & in a descent is a Good Thing? It demonstrates efficient aerodynamics... 

Of course. However, see my point above: it goes to waste if you end up with the speedbrake out all the time. 

You use the speedbrake because you have too much energy. The amount of energy you have is a function of height (gravitational potential energy) and speed (kinetic energy). You obtain both by converting fuel (chemical energy) in to thrust.

When you close the thrust levers at top of descent you (for all intents and purposes) stop converting fuel in to kinetic energy. To maintain airspeed therefore you have to descend - converting your gravitational potential energy in to kinetic energy. If you level off without adding thrust, you are now converting your kinetic energy back in to gravitational potential and so on. As you descend, your overall energy reduces (until ultimately you stop on the runway and you have KE=0 and GPE=0).

Having a slippery airframe reduces the rate at which energy is 'lost' to noise/heat/creating turbulence in the air etc. This allows you to close the thrust levers earlier and 'glide' further without additional thrust and therefore burn less fuel.

However, if you stay at cruise too long you are effectively pouring more and more energy in to the system. This energy comes from burning fuel. When you start down, you realise you have too much energy so you put the speedbrakes out in order to convert some of that 'extra' energy in to noise, turbulence etc. Effectively you are throwing away all the fuel you burnt between the 'ideal' descent point and the point at which you actually started down.

This is why some people make a point about speedbrake usage - because it is a fundamentally inefficient way to fly the aeroplane and if you have a choice (not always the case in the imperfect real world with ATC requirements) there are more efficient ways to manage energy which result in an overall lower fuel burn and greater passenger comfort (speedbrakes are invariably noisy and vibration-inducing). As I say, the heating analogy above is a good way to think about it, or like racing up to a red traffic light in your car and standing on the brakes at the last moment - it works, but by anticipating ahead and getting off the gas earlier you burn less fuel and give your passengers a smoother ride - get off the gas early enough and you will barely have to touch the brake at all, though this may not always be practical in busy traffic! (Of course, if you get off the gas too early you may coast to a stop before you get to the stop line, and thus have to get back on the gas again - which is also less efficient than the 'ideal' profile).

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If our sims had a proper ATC built in with a prerequisite of maintaining separation and assigned airspeeds on approaches, the stigma of using the speedbrake would be a thing of the past.  

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More than Flaps  10 with speedbrakes is prohibited to airflow interference with the tail.

In most cases more fuel will be saved if the descent is started immediatly cruise altitude is reached.  This however would cause huge problems with cutting across levels and 2 aircraft could make an even more sudden decent.

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