a question for commercial pilots... when landing a jetliner the speed brake seems to deploy on its own. But its not on full

correct? I mean you have to pull it towards you and then it throttles up the engines in reverser mode...?? is that correct?

do you sometimes just leave it alone if you feel you don't need any reverse thrust??

Great question,

First lets chat about the types. You will hear the terms speed brakes and ground spoilers. On some aircraft, they are the same panels, but in others they are separate panels. Usually, the name really differs in whether you are in the air or on the ground. When the panels are the same, it's usually based on the max angle/throw used inflight and on the ground. But, on other aircraft, the ground spoiler panels will not be used in flight, only on the ground. Now that I have confused you enough, lets go further.

Now, speed brakes are basically panels that will have a variable throw/angle in flight to cause drag. This is why they are called speed brakes. As mentioned before, all panels may be used in flight or just the outboard ones that are also roll assist panels. Not only do they cause drag through the speed brake handle, they also move with the yoke/stick to assist in roll control. Even when deployed, they will still move and adjust to assist in roll. Now lets talk ground spoilers.

Ground spoilers are used on the ground and their purpose is to disrupt lift on the ground. When you touch down, the aircraft is still flying. The ground spoilers lift to an angle to dump lift and make the aircraft settle by transferring the weight from the wings to the wheels. This aids in braking as well as creating drag. Now, we mentioned that some aircraft use the same panels for both. In that case, in flight, they are limited to a max angle. On the ground they have a higher angle. For example, they may be limited to 30 degrees in flight(roll assist panels could be 40 degrees) and 70 degrees on the ground. On aircraft with ground spoiler panels that don't move inflight, those panels will join the others once on the ground. Now lets talk about the action you described.

Most ground spoilers in modern times are automatic and can be armed before landing. When the weight on wheel switches compress or when wheel spin up is sensed, they will automatically deploy to their designated position. You arm them through a switch or by lifting the handle to the armed position. This action is also used for takeoff on some aircraft. If the throttles are reduced on takeoff roll, the ground spoilers will automatically deploy to assist with braking as it does on landing. If the automatic function fails, you have to manually deploy them. Most handles are restricted to the max angle in flight and become unblocked once on the ground. There are also lockouts on some aircraft depending on flap usage.

Ground spoilers are also factored in takeoff and landing performance. If they are inop or not used, you have to make takeoff distance and landing distance corrections because of the penalty.

 

Edited January 12, 20233 yr by G550flyer

I think he might be getting mixed up between speed brakes and reverse thrust. 

 

22 minutes ago, martin-w said:

I think he might be getting mixed up between speed brakes and reverse thrust. 

Good Point,

Now reverse thrust is not automatic and has to be initiated by the pilot. Most engines will have FADECs or other controlling systems that will either limit the N1 speed or the EGT that you will get when engaging reverse thrust. There are some who will meter how much reverse thrust they will use. Like, if it's a long runway, they may select reverse idle and ride it till slowing to a point with braking. I have also seen guys/gals select a high amount and then quickly return to reverse idle. There are aircraft specific speeds at which you need to be at reverse idle and forward idle. It may be reverse idle by 60 or 50 knots and forward by taxi speed. This prevents FOD ingestion risk from the reversed air kicking up debris. In the Gulfstreams(G5 or better), we actually use reversers during taxi. One reverser at idle to maintain speed and two reveresers at idle to slow down before a turn. You get so good at it that you never really touch the brakes until stopping. The brakes are really grabby once they are warmed up. The jet has a tendancy to get fast during taxi at idle. Either way, you initiate it on takeoff and landing. When I flew DC10s, you were restricted to reverse idle until the nose was down. Only the number 2 engine would be locked to reverse idle, but if you tried 1 and 3, they would go past reverse idle. It's always fun constantly lifting on the reverse handles while awaiting the number 2 interlock to release so that you could lay into max reverse. Good times! 

Well, whether it's speed brakes, ground spoilers or reversers, we have it all sorted.

Edited January 12, 20233 yr by G550flyer

1 hour ago, G550flyer said:

In the Gulfstreams(G5 or better), we actually use reversers during taxi. One reverser at idle to maintain speed and two reveresers at idle to slow down before a turn. You get so good at it that you never really touch the brakes until stopping. The brakes are really grabby once they are warmed up. The jet has a tendancy to get fast during taxi at idle.

That's quite interesting. I wonder why not taxi in/out with one or two engines out (if the case) versus using reversers during taxi to slow down, so much for fuel conservation. 

11 minutes ago, LRBS said:

That's quite interesting. I wonder why not taxi in/out with one or two engines out (if the case) versus using reversers during taxi to slow down, so much for fuel conservation. 

That's a good question. When you get into the biz jet world, everything is about passenger comfort and time. Fuel is not a big issue in these jets because they are super efficient. When you get up to altitude, the jet sips fuel. In fact, we will sacrifice fuel for time routinely. Airlines are very fuel minded, which makes sense when you have a large fleet of aircraft. You will notice that airliners have not gotten faster over the years. They will let you set on that jet for a longer period as long as fuel burn is low. Biz jets on the other hand have gotten faster. A G5 at .83 reaching 6000NM up to a G8 at .90 reaching 7000NM. It's already announced that both major companies are working super sonic biz jets. To put it in perspective, on some of my typical routes, the difference between cruising at .80 and .85 have been 500 to 1000 pounds of fuel. In the biz world, time is money. You always keep a "ready to go" posture. No ground equipment and APU running as soon as power is on. When the vehicle pulls up, right engine starts spinning. As the principal hits the stairs, left engine starts spinning. The last thing you want to do is get near the end of the runway and find out an engine will not start. You will have to taxi back in. In most cases, you are holding short ready to go by the time the 3 minute warm up period happens.  

The reverser during taxi came about because they sit high and FOD is relatively low at reverse idle. Reverser use for taxi speed control was preferred over having to start the engine when taxi time is 5 minutes or less. 

Yeh, what can I say, previously dual-qualified in B748 @  0.85 Mach and 7,700 nm range, and A389 @  0.85 Mach with a range of 8,000 nm, and now on B789 @  0.85 Mach with over 7,500 nm range I find them quite good and of course main target, pax comfort which I doubt seriously when we all know what they did with the seating configurations. 

We taxi in/out with one/two engines based on the weights, and as you mentioned the 5 minutes we have that limitation before t.o.

It's so much to learn in this business and how companies operate. For sure, every day/flight we learn something in this trade and it never stops. 

Edited January 12, 20233 yr by LRBS