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De-acceleration options at touch down

Posted: Tue Jul 12, 2016 4:37 pm
by LZBTW
Hello dear formers,

I apologise if this topic had been raised before but I couldn't find it. My question is about the useage of the brakes, spoilers and reverse thrust during a landing. I had a flight (FR4081) on a Boeing 738 last month to Fuerteventura and the runway there is not too long for landings, so when we landed I was expecting some harder de-acceleration but instead the spoilers were not raised - it was just reverse thrust and brakes, and it was a very long landing, which I haven't seen before and I have at least 2-3 flights every month so I was very surprised. I was going to go and ask the pilots after the flight while at the gate why that is but the crew told me people can't go in the cockpit. I started looking around and I read sometimes on rare occasions spoilers won't work and flights can still go ahead before the plane goes for maintenance but on this case I saw the spoilers work during the descent when we had to lose a bit of speed. And I never understood why would you not use the spoilers when they work as they'll provide extra downforce and help with braking. Yesterday night though I was flying in to Manchester (EGCC) from Madeira on U2 1958, the weather in Manchester was awful and the runway was really wet and yet we used only the brakes and speedbrakes, no reverse thrust was used, which really really surprised me as the runway was so wet brakes wouldn't have been as efficient as on a dry runway. I want to find out now why would crew use all 3 systems sometimes and some other times rather wouldn't deploy spoilers or reverse thrust on landing? Is there anything to do with weather or saving costs as both cases were on low cost airlines? Is it as save not to use them all? Thank you very much for the information and advise.

Re: De-acceleration options at touch down

Posted: Tue Jul 12, 2016 5:41 pm
by greg85
Hi there. Actually the runway at GCFV is very long, it's just over 3000m.

I'm surprised about your Ryanair flight, you'd expect to see the ground spoilers upon touchdown. Maybe there was some kind of fault there?

As for your EasyJet flight, I'm pretty sure that they will have used "reverse idle", which is standard at EasyJet (and a great many other airlines). The main reason not to use "reverse max" is noise. It's certainly available when required, but again EGCC has big runways for an A320.

A bit of extra info: the wheel brakes provide most of the deceleration, the spoilers are really there to put the weight on the wheels. Reverse thrust is more effective at high speed, and becomes less effective during deceleration. Often the reason to use more reverse thrust is to keep the brake temperatures lower, rather than have more deceleration. On the A320, under normal circumstances, the use of reverse max should be avoided below 70kts. Mainly because we don't want to hoover the runway!

Re: De-acceleration options at touch down

Posted: Tue Jul 12, 2016 9:04 pm
by LZBTW
Yes I knew the ground spoilers help to provide a lot of downforce and that is why I was so surprised when they were not used. You said that most probably there was a technical fault, would this affect the planend for the flight back, would be a major concern for the landing back into Liverpool airport? And as you said sometimes airlines don't use full reverse thrust, which once worked out quite badly for G-EZOF at MAN as its brakes got too hot and started smoking, and they had to scramble a few firetrucks, but in the case last nightnight there was no reverse thust at all, maybe they were saving some extra fuel :D who knows... And also about GCFV the runway is very long for take off but for landings, from the piano keys, you only have about 2000m and that's what I meant as it's a bit shorter than usual.

Re: De-acceleration options at touch down

Posted: Tue Jul 12, 2016 10:49 pm
by aklrno
Looking on google maps satellite view I notice that the runway is very long but with huge displaced thresholds on both ends. The result is that the touchdown zone is about 1/3 of the way down the runway heading north and there is a good chance that no matter the deceleration rates you need to go nearly all the way to the end of the runway to turn off onto the taxiway. Why not get there as soon as possible and save wear on the engines and brakes?

Re: De-acceleration options at touch down

Posted: Wed Jul 13, 2016 2:23 am
by tb727
LZBTW wrote:
I want to find out now why would crew use all 3 systems sometimes and some other times rather wouldn't deploy spoilers or reverse thrust on landing? Is there anything to do with weather or saving costs as both cases were on low cost airlines? Is it as save not to use them all? Thank you very much for the information and advise.


As far as spoilers go, I have always always always deployed them on touchdown in transport category aircraft. It is very rare and it's quite possible they forgot to deploy them or there could have been an issue on landing that prevented them from deploying.

As far as brakes vs reverse thrust, it's normally a pilots preference but could be dictated by airline SOP. We have a pretty relaxed SOP as far as that goes so it's nice they leave it up to our techniques and I am at a ULCC, cheap shouldn't mean not safe. My preference on a dry runway is to use manual brakes and max reverse(idle reverse if I'm light and rolling it far down the runway), usually I don't use the brakes until below 60-70 knots to keep them cool. The Airbus brakes can get annoyingly hot if you are doing a quick turn and don't have brake fans. Crosswind and/or wet runway I will use auto brakes and max reverse again. Guess my preference is max reverse, I like noise maybe. Same thing when I was on the 727 with max reverse, we didn't have auto brakes though and we had to pull the spoilers on touchdown so it was muscle memory as a Captain and a required call out.

I'm not a big fan of using hard application of brakes unless it's necessary because I was raised by an aircraft mechanic. Suppose I drive my truck the same way. I downshift to slow most of the time and am easy on the brakes because I'm the one that has to change them.

Re: De-acceleration options at touch down

Posted: Wed Jul 13, 2016 6:11 am
by LZBTW
I think these answers explain my question quite well and I very much appreciate it, thank you all for the use full insights and the information :)

Re: De-acceleration options at touch down

Posted: Wed Jul 13, 2016 6:37 am
by aklrno
tb727 wrote:
LZBTW wrote:
I'm not a big fan of using hard application of brakes unless it's necessary because I was raised by an aircraft mechanic. Suppose I drive my truck the same way. I downshift to slow most of the time and am easy on the brakes because I'm the one that has to change them.


My Ferrari mechanic used to laugh at people using the transmission to slow the car. It was great for business. A clutch replacement cost about a week and $10,000. The brakes pads were a few hundred dollars and could be replaced in minutes. The brakes are designed to slow the car. The clutch is not. I'd like to know what the design engineers think is the right way to slow down.

Re: De-acceleration options at touch down

Posted: Wed Jul 13, 2016 8:27 am
by greg85
Just to answer back to a few points. The LDA on 01R in GCFV is 2406m, so really it's not not short and wouldn't require much braking effort from the crew.

On the Ezy flight, no reverse is something that would be flagged up by flight data monitoring (unless the were both inop, which is unlikely). Are you sure there was no reverse? There are only a few seats on the plane that would allow you to see.

Re: De-acceleration options at touch down

Posted: Wed Jul 13, 2016 1:25 pm
by LU9092
aklrno wrote:
tb727 wrote:
LZBTW wrote:
I'm not a big fan of using hard application of brakes unless it's necessary because I was raised by an aircraft mechanic. Suppose I drive my truck the same way. I downshift to slow most of the time and am easy on the brakes because I'm the one that has to change them.


My Ferrari mechanic used to laugh at people using the transmission to slow the car. It was great for business. A clutch replacement cost about a week and $10,000. The brakes pads were a few hundred dollars and could be replaced in minutes. The brakes are designed to slow the car. The clutch is not. I'd like to know what the design engineers think is the right way to slow down.



If you're doing it right, downshifting to decelerate doesn't wear the clutch at all. If you're really good at matching revs, you don't even need to disengage the clutch.

Re: De-acceleration options at touch down

Posted: Wed Jul 13, 2016 3:39 pm
by tb727
LU9092 wrote:
aklrno wrote:
tb727 wrote:


My Ferrari mechanic used to laugh at people using the transmission to slow the car. It was great for business. A clutch replacement cost about a week and $10,000. The brakes pads were a few hundred dollars and could be replaced in minutes. The brakes are designed to slow the car. The clutch is not. I'd like to know what the design engineers think is the right way to slow down.



If you're doing it right, downshifting to decelerate doesn't wear the clutch at all. If you're really good at matching revs, you don't even need to disengage the clutch.


Guess my Dodge truck nearing 200k miles is a little tougher than your Ferrari.

Re: De-acceleration options at touch down

Posted: Wed Jul 13, 2016 8:35 pm
by aklrno
tb727 wrote:
LU9092 wrote:


If you're doing it right, downshifting to decelerate doesn't wear the clutch at all. If you're really good at matching revs, you don't even need to disengage the clutch.


Guess my Dodge truck nearing 200k miles is a little tougher than your Ferrari.


No doubt. My Toyota Tercel was way tougher than a Ferrari!

Re: De-acceleration options at touch down

Posted: Fri Jul 15, 2016 2:49 am
by OzzyPirate
Are you sure there was zero spoiler deployment? Spoilers/speedbrakes are crucial to braking performance -- losing an entire hydraulic system on the 738 will still leave half the spoilers operational, they're checked as armed during the landing checklist, and they're verified up immediately after touchdown.

It's possible they had a situation which called for manual speedbrake extension on landing (there are a few) and missed them completely.

Re: De-acceleration options at touch down

Posted: Sat Jul 16, 2016 7:09 pm
by WingedMigrator
LZBTW wrote:
Yes I knew the ground spoilers help to provide a lot of downforce


They don't really provide downforce; they just spoil the lift generated by the wing. Gravity provides the downforce.

Re: De-acceleration options at touch down

Posted: Sat Jul 16, 2016 8:22 pm
by bueb0g
aklrno wrote:
tb727 wrote:
LZBTW wrote:
I'm not a big fan of using hard application of brakes unless it's necessary because I was raised by an aircraft mechanic. Suppose I drive my truck the same way. I downshift to slow most of the time and am easy on the brakes because I'm the one that has to change them.


My Ferrari mechanic used to laugh at people using the transmission to slow the car. It was great for business. A clutch replacement cost about a week and $10,000. The brakes pads were a few hundred dollars and could be replaced in minutes. The brakes are designed to slow the car. The clutch is not. I'd like to know what the design engineers think is the right way to slow down.


Then your Ferrari mechanic either has a) no idea what a clutch is and what it does or b) doesn't know how to drive. Engine braking is more efficient and better for wear and tear than using the wheel brakes.

Re: De-acceleration options at touch down

Posted: Tue Jul 19, 2016 4:52 pm
by Classa64
I thought SOP would be " Spoilers Armed" on the before landing checklist? Or is it different for every plane.

Re: De-acceleration options at touch down

Posted: Tue Jul 19, 2016 7:35 pm
by BoeingGuy
Classa64 wrote:
I thought SOP would be " Spoilers Armed" on the before landing checklist? Or is it different for every plane.


Spoilers armed are on the Boeing Landing checklist. The Boeing procedure also calls for a callout by the Pilot Monitoring to confirm "SPEEDBRAKES UP" or "SPEEDBRAKES NOT UP" after touchdown.

The 787, 747-8, and KC-46 also have a Time Critical Warning with an aural and text on the PFD that says "SPEEDBRAKE" if the speedbrakes are not up during landing rollout or RTO.

Re: De-acceleration options at touch down

Posted: Wed Jul 20, 2016 10:06 pm
by hivue
BoeingGuy wrote:
Classa64 wrote:
The Boeing procedure also calls for a callout by the Pilot Monitoring to confirm "SPEEDBRAKES UP" or "SPEEDBRAKES NOT UP" after touchdown.

The 787, 747-8, and KC-46 also have a Time Critical Warning with an aural and text on the PFD that says "SPEEDBRAKE" if the speedbrakes are not up during landing rollout or RTO.


I always thought "speed brakes" and "ground spoilers" were different things in the sense that all the panels are deployed for the latter and only some for the former. Are the two terms actually interchangeable?

Re: De-acceleration options at touch down

Posted: Wed Jul 20, 2016 11:34 pm
by OzzyPirate
hivue wrote:
BoeingGuy wrote:
Classa64 wrote:
The Boeing procedure also calls for a callout by the Pilot Monitoring to confirm "SPEEDBRAKES UP" or "SPEEDBRAKES NOT UP" after touchdown.

The 787, 747-8, and KC-46 also have a Time Critical Warning with an aural and text on the PFD that says "SPEEDBRAKE" if the speedbrakes are not up during landing rollout or RTO.


I always thought "speed brakes" and "ground spoilers" were different things in the sense that all the panels are deployed for the latter and only some for the former. Are the two terms actually interchangeable?


In Boeing terminology, "spoiler" is used to describe the devices/panels themselves -- so there are ground spoilers and flight spoilers, for a total of 12 spoilers on the 737. The term "speedbrake" is used to describe the system as a whole, whether we're in the air or on the ground. To put it another way, the speedbrake system is comprised of flight spoilers and ground spoilers.

Re: De-acceleration options at touch down

Posted: Thu Jul 21, 2016 6:14 am
by Starlionblue
OzzyPirate wrote:
hivue wrote:
BoeingGuy wrote:


I always thought "speed brakes" and "ground spoilers" were different things in the sense that all the panels are deployed for the latter and only some for the former. Are the two terms actually interchangeable?


In Boeing terminology, "spoiler" is used to describe the devices/panels themselves -- so there are ground spoilers and flight spoilers, for a total of 12 spoilers on the 737. The term "speedbrake" is used to describe the system as a whole, whether we're in the air or on the ground. To put it another way, the speedbrake system is comprised of flight spoilers and ground spoilers.


On the 'bus, it is "speedbrake" in the air and "ground spoilers" on the ground. Same lever though.

Re: De-acceleration options at touch down

Posted: Thu Jul 21, 2016 2:51 pm
by hivue
OzzyPirate wrote:


stationblue wrote:


Thanks for the info. Another question: at landing I gather that the purpose of the speedbrakes/ground spoilers is to "spoil" lift in order to get max weight on the wheels for braking, which -- along with reverse thrust -- is what actually accomplishes the speed reduction. In the air, though, are the speedbrakes primarily intended to reduce airspeed or are they instead primarily intended to spoil lift and thus increase rate of decent?

Re: De-acceleration options at touch down

Posted: Thu Jul 21, 2016 3:33 pm
by Whiteguy
hivue wrote:
OzzyPirate wrote:


stationblue wrote:


Thanks for the info. Another question: at landing I gather that the purpose of the speedbrakes/ground spoilers is to "spoil" lift in order to get max weight on the wheels for braking, which -- along with reverse thrust -- is what actually accomplishes the speed reduction. In the air, though, are the speedbrakes primarily intended to reduce airspeed or are they instead primarily intended to spoil lift and thus increase rate of decent?


Pretty much, the spoilers on the '37 don't do a lot in the way of reducing speed....

Re: De-acceleration options at touch down

Posted: Thu Jul 21, 2016 8:58 pm
by Starlionblue
hivue wrote:
OzzyPirate wrote:


stationblue wrote:


Thanks for the info. Another question: at landing I gather that the purpose of the speedbrakes/ground spoilers is to "spoil" lift in order to get max weight on the wheels for braking, which -- along with reverse thrust -- is what actually accomplishes the speed reduction. In the air, though, are the speedbrakes primarily intended to reduce airspeed or are they instead primarily intended to spoil lift and thus increase rate of decent?


They are used for either or both. It depends what you are trying to do at a particular time. Airliners are very "slippery" and tend to want to keep going.

Both decelerating and descending (faster) at the same time is possible, but not as efficient. As the saying goes "you can go down or slow down, not both." Ideally, you'd "go down" first at a higher speed (meaning higher RoD), then slow down.

Examples:
Altitude loss: You're on approach at 250 knots at 10000 feet, cleared down to 5000 feet and above profile. Keeping 250 knots selected, you pull speedbrake. This will increase the rate of descent.
Speed loss: You're on approach at 300 knots at 10000 feet, and need to maintain 10000 feet but slow to 230 knots. Keeping 10000 knots selected, you select 230 knots. Pulling speedbrake will increase the deceleration rate.

Re: De-acceleration options at touch down

Posted: Fri Jul 22, 2016 6:12 am
by Florianopolis
Starlionblue wrote:
Speed loss: You're on approach at 300 knots at 10000 feet, and need to maintain 10000 feet but slow to 230 knots. Keeping 10000 knots selected, you select 230 knots. Pulling speedbrake will increase the deceleration rate.


Just so we're clear about using the spoilers for speed loss - the spoiler kills the wing's lift generation, so you pull up the nose and increase the angle of attack to maintain your altitude...which increases drag (I'm guessing) substantially more than the drag of the spoiler in the slipstream...? This would be different than the literal speedbrakes on some jets (BAE146, F-14) that work by directly adding drag?

Separately - I've always been under the impression that if you're piloting a jet airliner, and need to go down and slow down, you're usually better off by first slowing down at your current altitude, and then throwing out flaps and landing gear, and then most airliners will drop like rocks. Is that accurate?

Re: De-acceleration options at touch down

Posted: Mon Jul 25, 2016 5:18 am
by Starlionblue
Florianopolis wrote:
Starlionblue wrote:
Speed loss: You're on approach at 300 knots at 10000 feet, and need to maintain 10000 feet but slow to 230 knots. Keeping 10000 knots selected, you select 230 knots. Pulling speedbrake will increase the deceleration rate.


Just so we're clear about using the spoilers for speed loss - the spoiler kills the wing's lift generation, so you pull up the nose and increase the angle of attack to maintain your altitude...which increases drag (I'm guessing) substantially more than the drag of the spoiler in the slipstream...? This would be different than the literal speedbrakes on some jets (BAE146, F-14) that work by directly adding drag?


Correct. Speed brake out. Less lift means a pitch angle increase to maintain altitude. And as you slow down more pitch angle increase until you retract the speedbrakes. The pitch angle change is not very noticeable though.

In the 333 you'll lose around 10 knots per nautical mile in level flight without speedbrake. With speedbrake it goes up to about double if memory serves.


Florianopolis wrote:
Separately - I've always been under the impression that if you're piloting a jet airliner, and need to go down and slow down, you're usually better off by first slowing down at your current altitude, and then throwing out flaps and landing gear, and then most airliners will drop like rocks. Is that accurate?


The typical method is to keep your speed up and descend faster, then slow down. If you slow down early, you'll just descend slowly. If you're at, say, 18000 feet and you need to descend quickly, you're not going to put out flaps and gear because you most likely don't want them out later. Certainly speed brake can be used as needed.

Now, if you're lower, say 5000AAL, and you're sure you're not going to be retracting them later, by all means throw out flaps and gear earlier than usual. However you'll still descend faster at a higher speed.

To give you an idea of how slippery jetliners are, in the 333 if you're on a 3 degree glideslope at Flaps 2, you'll be at idle thrust. At Flaps 1 or 0, you won't be able to keep your speed down without speedbrake, and even that is hard.

Re: De-acceleration options at touch down

Posted: Mon Jul 25, 2016 9:22 pm
by vikkyvik
Florianopolis wrote:
Just so we're clear about using the spoilers for speed loss - the spoiler kills the wing's lift generation, so you pull up the nose and increase the angle of attack to maintain your altitude...which increases drag (I'm guessing) substantially more than the drag of the spoiler in the slipstream...? This would be different than the literal speedbrakes on some jets (BAE146, F-14) that work by directly adding drag?


It's not one or the other - speedbrakes (flight spoilers) will reduce the wing's lift, but also add drag, even before the nose is raised to maintain altitude.

aklrno wrote:
My Ferrari mechanic used to laugh at people using the transmission to slow the car. It was great for business. A clutch replacement cost about a week and $10,000. The brakes pads were a few hundred dollars and could be replaced in minutes. The brakes are designed to slow the car. The clutch is not. I'd like to know what the design engineers think is the right way to slow down.


You don't use the transmission to slow the car down. You use the engine to slow the car down (just like you use the engine to speed up). Properly downshifting won't really add any more wear than properly upshifting.

If people are wearing out the clutch due to engine braking, then they simply don't know how to drive a stick shift. I'm not surprised at all, especially in an expensive and high-powered car like a Ferrari.

Re: De-acceleration options at touch down

Posted: Tue Jul 26, 2016 10:35 pm
by aklrno
It is hard to control engine speed to match the clutch speed with a manual clutch in a very high power engine. That's why brakes are preferred. It's different in the "F-1" transmissions (paddle shifters) that are electronically controlled with twin clutches. Don't completely know how they do it but it's all over in about 50 milliseconds and very smooth. I don't think Ferrari even makes cars with manual clutches any more.