[airforce1]

Originally Posted by Jeroen

Sorry, but I dont think that's entirely correct. I don't think reverse thrust does not affect the life of engines by any relevant margin. Number of hours and number of starts determine the life of turbine engines. They don't count the number of reverse thrusts, the do count the number of hours and the number of starts.

Although I'm not that familiar with the airbus as far as know SOP is to use the auto braking system at all times. By aerodynamic braking he might think he's increasing the life of the brakes perhaps. Again, I'm not so sure. The airbus uses carbon brakes and the best you can do for those is to build up heat very fast indeed!

I seem to recall that the Airbus does have some system logic built in that prevents the auto brakes to come in to the preset settings until the nose gear is on the ground and the strut has been compressed. Again, another reason not to land like this. At what time does you auto brake system kicks in?? Anybodies guess.

You land single engine prop planes like this, you keep the nose of the ground as long as can, to avoid prop strike. The only plane I know that gets landed with an intentional nose up attitude for aerodynamic braking effect is the Vulcan. One of my very favorite planes. Probably something to do with a V-wing, the fact that it was British designed and made and probably had pretty crappy brakes to start with. They did not have carbon brakes in those days

Jeroen

Excellent information Sir, though I'd like to make a small correction, Reverse Thrust, on its own does not affect the life of the engine as you mentioned and it is indeed the hours and the number of cycles, not starts that determine the life of a turbine engine ( one cycle is one take off and landing), but there is something known as the effective maintenance cost of an engine (which , by the way , is the second highest cost to an airline industry after fuel! ). An engine's wear and tear is less, thereby reducing that cost margin. I'am not saying that reversers should not be used, but as a practise, mostly Idle reverse is used more predominantly. By the way in all the European Union Airports, it is required to use Idle Reverse for noise abatement purpose, unless Safety is compromised.

You are correct that SOP's recommend use of Auto brakes at all times, and its not only Airbus, but mostly all aircrafts! But it's recommended and the requisite conditions are given in the Relevant SOP's. Aerodynamic Braking has got nothing to do with the life of brakes!!! It is essentially the increment of drag that helps the aircraft slow down marginally, (though, I would not recommend this method personally.)

Not only Airbus, even Boeing, And the most Recent, Embraer, have the same system logic for activation of the Autobrake system. Autobrake comes into the preset setting when the Throttles are in idle position and the main gear wheels are spun up! So, with the main gear down and touched, the Autobrake system kicks in on the preset value and does its job!

Ideally, single engine or multiengine, the Aerodynamics of the aircraft remains the same. The landing geometry of all the aircrafts remains the same, it has got nothing to do with the size of the prop, the basic attitude is a slight nose up, to wash away the speed to the requisite value in accordance to the aircraft. It's a very vast topic for discussion, Aerodynamics of an Aircraft!

[ahmad.007]

This is one awesome thread we have here.
12 km/l per head is good considering the plane is cruising at 800-900 km/hr.
But, the overall efficiency would be I guess 12/180(people, guide me if I am wrong) km/l which is about 1km/15l !!! Not at all bad for a massive aircraft.

I have been a few times on the Airbus A320, and I feel the acceleration is pretty good and addictive. The plane starts rolling till 20-30 km/hr then suddenly you hear the pilot full-throttling the thrusters, the engines start howling and whining, but full bore acceleration only comes after about 4-5 seconds (turbine lag :lol or maybe delayed cluth release :lol) suddenly throwing every passenger back onto their seats and smoothly pinning them 1cm foam deep into the cushion. There after the acceleration is brisk and unending, more like a swift ddis pulling in 3rd gear with a constant gusto till a hypothetical redline of 50k rpm (I wish, hehe). So, considering my natural experience (no statistical data) the 0-100 should be around 30-35 seconds, but 100-200 should be impressive, in the league of say 8-12 seconds.
You only get to know the thrust when the plane leaves the ground and starts climbing effortlessly.
The landing part is very much like a bus on bad road. Noisy suspension. :lol

[Jeroen]

Originally Posted by airforce1

Excellent information Sir, though I'd like to make a small correction, Reverse Thrust, on its own does not affect the life of the engine as you mentioned and it is indeed the hours and the number of cycles, not starts that determine the life of a turbine engine ( one cycle is one take off and landing), but there is something known as the effective maintenance cost of an engine (which , by the way , is the second highest cost to an airline industry after fuel! ). An engine's wear and tear is less, thereby reducing that cost margin. I'am not saying that reversers should not be used, but as a practise, mostly Idle reverse is used more predominantly. By the way in all the European Union Airports, it is required to use Idle Reverse for noise abatement purpose, unless Safety is compromised.

You are correct that SOP's recommend use of Auto brakes at all times, and its not only Airbus, but mostly all aircrafts! But it's recommended and the requisite conditions are given in the Relevant SOP's. Aerodynamic Braking has got nothing to do with the life of brakes!!! It is essentially the increment of drag that helps the aircraft slow down marginally, (though, I would not recommend this method personally.)

Not only Airbus, even Boeing, And the most Recent, Embraer, have the same system logic for activation of the Autobrake system. Autobrake comes into the preset setting when the Throttles are in idle position and the main gear wheels are spun up! So, with the main gear down and touched, the Autobrake system kicks in on the preset value and does its job!

Ideally, single engine or multiengine, the Aerodynamics of the aircraft remains the same. The landing geometry of all the aircrafts remains the same, it has got nothing to do with the size of the prop, the basic attitude is a slight nose up, to wash away the speed to the requisite value in accordance to the aircraft. It's a very vast topic for discussion, Aerodynamics of an Aircraft!

Thanks, couple of add-ons.
I dont think engine maintenance, apart from fuel, is the biggest cost for carriers apart from fuel these days. C and in particular D checks are hugely expensive and apart from the cost, the aircraft is grounded for many weeks, so its not earning any revenue. Engine maintenance cycles have gone up steadily with new generations. Less maintenance, less frequently. I was talking to the CEO of one off India airlines over the weekend and he was more worried about his finance cost then engine maintenance cost so to speak. But he promised me to get some figures.

Technically speaking it's the start up of a turbine engine that puts wear an tear on it, and running hours. But the starting process is relatively speaking the hardest. Shutting down does't add to the wear and tear and process. But you are correct we count cycles.

Noise abatement procedures around the globe call for idle thrust reverse. Shouldn't be a big thing at all. Especially for planes with auto braking. Autobrakes decelerate the plane at a specific deceleration rate. Irrespective of speed or weight of the plane. Applying reverse thrust while the autobrakes are at work will not slow the plane down quicker. The autobrakes keep it at the preset deceleration rate. But it does mean the brakes have to work less. So using reverse thrust in combination with auto braking increases brake componenet life and I suppose to some extend even tire wear as well.

At a low auto brake setting in theory, the reverse thrust could provide a higher deceleration rate than the autobrake system. In which case the brakes would not be working at all, so no wear and tear at all. Not sure if this is theory or whether it could happen in practice.

Every plane I know is allowed to take off with non operative thrust reversers, as long as it has operable (auto) brakes. No plane is allowed to take off with any problem to its braking system, no matter if the thrust reversers work. (All of course in line with MEL and relevant SOP for departing and destination/alt airport)

The reverse thruster do come into play with heavy precipitation, (rain), standing water on the runway, slush, landing with tailwind, relatively short runway and a few other conditions.

Some years ago I spent about 3 hours putting one of Lufthansa 747-400 Full Motion Simulator in Frankfurt through it's braking paces so to speak. We wanted to understand more in depth how the reverse thrust works in combination with the autobrakes. The 747 is also equipped with a very advanced ABS and anti skid system. So we wanted to figure out under which conditions applying reverse thrust would give a noticeable difference over the autobrake system. We had lots of fun, I added some 30 more landings to my experience, but I seem to recall we did not reach any firm conclussions.

By the way, the simulator is the only place where my number of take offs and landing doesn't add up to an even number! In fact my simulator landings outnumber the simulator take offs by a very large margin!

If anything our conclussion was that in most cases, thrust reversers are used to prolong brake component life, nothing else. Maybe we ran into limitations of the simulator. Although at the time it was the most advanced one money could buy. Trust the Germands to get the best!

The interlocking logic for the autobrakes is a little bit more complicated than you describe. I seem to recall 8-11 pre -conditions need to exist before the system engages. I would have to look it up. I did not bring any of my aviation manuals to India. My whole aviation library is in my home in the Netherlands. I'll be there next week. Be fun to dig in some of the manuals, to figure it out. Most of my library is on Boeing and Boeing related OEM manufacturers and procedures, but I think I have a few AOMs on the earlier Airbus 320 series.

I do know though, that on the Airbus the nose gear plays a role in the interlocking sequence for the autobrake system. Maybe Ifly knows as he is supposed to be an Airbus driver. He should know or have access to the relevant manuals. Would be nice to hear from him on some of these slightly more indepth topics.

I seem to recall a long discussion on Prune about not being able to set the Airbus autobrake to MAX, unless the nose gear oleo was fully deflected. Never understood the logic of that. But even the guys on Prune couldn'r reach consensus on this one.

On aerodynamic braking, it does reduce brake wear! Maybe only by a small margin, but what it does is it reduces the speed at which you, or the autobrake system, starts applying the brakes. If you start braking at a relatively lower speed there is less dynamic energy to get rid off, thus reducing the wear and tear on the brake system components.

Of course, as discussed before you tend to eat up a lot of runway.

Have a look at this video of a Vulcan landing, talk about aerodynamic braking to the max:

http://www.youtube.com/watch?v=bY_CRipaxBE

Jeroen

[Jeroen]

Although I have accumulated quite a few hours flying, although not as much as commercial pilots, I have very few photographs or videos of me piloting. Always to busy flying. Never got around installing video cameras in the planes I flew.

So this one is pretty rare from that perspective; Me landing a Cirrus R20 on Catalina Island, of the coast of Los Angeles. Interesting flying around LA, never experienced VFR corridors before. I prefer IFR anyway. Around LA most mornings its always IMC conditions, so you wont get to go very often or very far without an IFR rating and IFR capable/certified plane.

Catalina island is considered to be a bit of challenge to land.
See http://abcnews.go.com/blogs/lifestyl...iest-airports/

Anyway, here's me doing my thing, with my daughter filming

http://www.youtube.com/watch?v=HRjUASwNz0g

I love the Cirrus and have flown it extenisvely since. Great cross county plane. It has a full glass cockpit based on the Garmin 1000. Interesting enough this gives me a more advanced suite of avionics then you would find in your typical Boeing 747-400! Lovely autopilot, but no autothrottle on this particular version. Which means you need to control the throttle yourself during descent/ascend.

The autopilot can bring me in to land all the way over the threshold and you only fly manual the last bit towards the flare an the actual touch down if you so desire.

You'll notice no yoke, this plane has a side stick. Not fly by wire, its all mechanically linked. And it has a parachute! If all fails you yank a handle and the plane simply floats back to earth on a huge parachute. Its the one option I haven't tried yet, but I have gone through the motions on the Cirrus simulator.

Enjoy,

Jeroen

[akp]

Originally Posted by Jeroen

Anyway, here's me doing my thing, with my daughter filming

Jeroen, immensely enjoying your posts on this thread (also your blog on India - but that's off topic here).

Just wanted to point out that there is some permission related problem with the video - it says "this video is private" when I try to view it.

[Jeroen]

Originally Posted by akp

Jeroen, immensely enjoying your posts on this thread (also your blog on India - but that's off topic here).

Just wanted to point out that there is some permission related problem with the video - it says "this video is private" when I try to view it.

Thanks, it was somehow set to private, I changed it to public, so now you should be able to access

Jeroen

[carzone]

Originally Posted by Jeroen

Thanks, it was somehow set to private, I changed it to public, so now you should be able to access

Jeroen

Still the same. Me thinks you would have to copy and paste the link again.

[RemingtonSteele]

Jeroen: The video is still marked private and not availble for viewing.

Thanks Guys; for enlightening us with all this flying know-how and different terminologies associated with it.

[amitwlele]

This thread is simply amazing. Have been following it since it started and the abundant information that has been shared by different folks is greatly appreciated.

Thought would post to say my Thanks to everyone as the button is not present for this sub forum topic.

[Jeroen]

Originally Posted by RemingtonSteele

Jeroen: The video is still marked private and not availble for viewing.

Thanks Guys; for enlightening us with all this flying know-how and different terminologies associated with it.

Sorry my bad. I changed the setting to public but forgot to save it. Just redid it and checked to see if it works from my wife's computer. Should be good now!

Enjoy,

Jeroen

[amitwlele]

Originally Posted by Jeroen

Sorry my bad. I changed the setting to public but forgot to save it. Just redid it and checked to see if it works from my wife's computer. Should be good now!

Enjoy,

Jeroen

Yup it works now. Thanks.

It looks like the runaway is on top of a hill. Is that correct? Surely must be very challenging.

[Jeroen]

Originally Posted by amitwlele

Yup it works now. Thanks.

It looks like the runaway is on top of a hill. Is that correct? Surely must be very challenging.

Yes, it is right on top of a hill at roughly 1700 feet. The sides of the hill drop off sharply on both ends. So it is very difficult to get a good orientation. And its a VFR approach only. On top of that there are always stiff winds and gusts. And a lot of the time there are clouds about. You can see the clouds around us as well.

Theres should be a VASI to help you in the approach, but if there is one it certainly wasn't working the day I landed.

See for more details:

http://www.airnav.com/airport/KAVX

This was my first landing ever with a Cirrus R20 and I had not flown for a few months. Although the approach is good I'm landing a little bit of centre to the left due to cross wind. You can see me correcting all the way down as I dip the right wing to align. Still, it wasn't too bad. Once I flare you can hear a buzzer going off. This is the stall warning. Essentially, that is how you land these little planes. You need to bring them in on final, flare and stay just a feet or so above the runway. Then the airspeed will start to decay and you hold the nose up, avoid prop strike, the wings will stall, the stall buzzer will go off and you settle very nicely onto the runway. The runway is very uneven as you'll notice. Nothing to do with me, just lots of potholes!

The guy next to me is the CFI. Certified Flight Instructor. Although I'm perfectly legal and fully qualified to fly this plane it is not advisable to do so if you're not familiar. Hence the CFI. Safety first at all times!

I have flown a number of different planes and whenever I transition to a new type I will always spend at least a few hours flying with a CFI to show me the ropes, get familiar, before I will go out on my own.

Typically you want to spent some time "in the pattern", meaning flying around the airport doing touch and go's familiarizing yourself with the take off and landing characteristics. The other maneuvers I always placed a lot of emphasize on, when transitioning, was cross wind landings.

You really need to get 20+ crosswind landings under your belt on any type to feel a bit confident. That is on top of the 70-80 I did in basic training for my PPL. For some, these maneuvers come naturally. I'm quite comfortable doing cross wind landing up to 15-20 knots no problem. But I had to practice a lot. I had a friend for whom it came more or less naturally. The one thing that came very naturally to me is "forward slip". Again a standard maneuver and you have to demonstrate it during your check ride. Never had a problem with it and others found it difficult to master. Just how it goes, some come easy some you need to work hard for.

In all honesty I can say that learning to fly and flying around the USA all by myself is one of the most incredible achievements and experiences.

I know I was lucky being able to afford it, but still. Even the ones that can afford it, are often not very successful. I enjoyed every minute of it. Every time I took of or landed it brought an immense feeling of achievement.

My last flight in the US was a pretty difficult one. We took of from a small field near St Louis and flew to our home base, New Century Air center. All the way IMC. Never saw the sky, we broke out from under clouds only 100 feet above our landing minimums and touched down just fine.

As part of cost cutting, New Century Air center tower operation has now ceased, together with some other 148 airports.

See http://www.usatoday.com/story/travel...sures/2009371/

It's a real shame. These were not small airports by any stretch of the imagination. Now they are left without tower operation. Not saying it is unsafe, there is different practices and rules landing on these airports now. But it was always nice to be talking to the controllers. American controllers are very, very good, lots of patience and very accommodating. A lot of them are (private) pilots too. That makes a huge difference.

The FAA puts a lot of emphasis on safety training, see http://www.faasafety.gov/WINGS/pub/learn_more.aspx

I was a very enthusiastic participant of their wings program. Aimed at GA it's goal is to increase overall safety and reduce accidents.

I remember I went to one of their seminars. Topic was how to reduce fatal accidents in GA. The FAA has a lot of data pertaining on this. The most telling part of their analysis was that there is no correlation between hours flown and fatal accidents rate. Put differently, statistically speaking a new pilot with say 100 hours flying a Cessna 150 has the same statistical chance of being in a fatal accident as the captain of a Learjet with 10.000 hours.

The big differentiator was safety training and awareness. Pilots that engage in constant safey education/training are statistically speaking much less prone to end up in fatal accidents. The WINGS programs is exactly that, it constantly encourages pilots to study, read, be engaged in the broadest sense possible of enhancing your flying skills and your attitude. The latter probably being the most relevant.

There are other safety programs that do exactly the same. For instance Cirrus runs special (safety) programs for their owners. And statistically speaking those that participate crash 50% less then the pilots that don't participate.

So, its one of the reason I have put a few question to earlier poster on the "most stringent regime" here in India. Apart from the fact that nobody has answered my question what is so strict in India compared to other parts of the world, its not necessarily the rules and regulations that make airspace safe. Its the adherence to rules and regulations that make it safe. And no offense to anybody but my limited exposure here in India has shown me one thing, Indian don't adhere very well to rules and regulations.

I fly about 4-6 times a week with all of Indian carriers. And from what I can see none, and I mean, none of the cabin crews are anywhere up to where they should be in enforcing normal standard cabin practices. Just last week coming back from Leh on Air India, literally 90 seconds before touch down a lady unbuckles, gets up and takes her little daughter all the way back to the toilets. I checked, the stewardesses saw it happening, did not do anything. You try that sort of nonsense on American Airlines, KLM, BA, Virgin, Delta, SAS, Lufthansa and you will know the difference.

People get up whilst the plane is still taxing and the flight attendants don't take any actions. Its truly unbelievable.

Indian cabin crews do not exercise authority, they never ever speak up, they just go through the motion but don't add anything in terms of safety protocol or enforcement of safety protocol. Just my experience of a couple of hundred flight with Air India, Indigo, Jet Airways and Spice Jet, and a few others.

Air India is a case to its own, because I honestly have never ever witnessed such a complete and total disinterest of a cabin crew in their passengers as on our flight coming back from Leh last week.

The cockpit crew wasn't much better in terms of engaging with their customers. The plane left an hour earlier than the published time, only to sit on the tarmac with engines running for 35 minutes without any explanation, during or after.

My rule is; a captain that doesn't communicate with his passengers what goes on needs to be sacked immediately. Somebody who's lacking in basic communication skills and empathy can never be trusted to be any good in CRM (Crew Resource Management).

Jeroen

[revtech]

Originally Posted by Jeroen

On larger plane you tend to have a steering yoke/handle. Ie. a special yoke that directly controls the nose wheel.

its called a tiller

Originally Posted by Jeroen

When you pull up the wheels, providing you fly a plane with retractable gear, the wheels just spin. Even when retracted the wheels still spin, but of course, eventually they will stop spinning all together. Jeroen

Most commercial airliners have a device that stops rotation once airborne.

Originally Posted by Jeroen

Sorry, but I dont think that's entirely correct. I don't think reverse thrust does not affect the life of engines by any relevant margin.

use of reverse thrust affects wear and tear of the engine !!

Originally Posted by Jeroen

I seem to recall that the Airbus does have some system logic built in that prevents the auto brakes to come in to the preset settings until the nose gear is on the ground and the strut has been compressed. Again, another reason not to land like this. At what time does you auto brake system kicks in?? Anybodies guess.

autobrake activation has go nothing to do with the nose wheel.. it starts when the main wheels touch the ground and thrust levers in idle

Originally Posted by Jeroen

Thanks, couple of add-ons.
I dont think engine maintenance, apart from fuel, is the biggest cost for carriers apart from fuel these days. C and in particular D checks are hugely expensive and apart from the cost, the aircraft is grounded for many weeks, so its not earning any revenue. Engine maintenance cycles have gone up steadily with new generations. Less maintenance, less frequently. I was talking to the CEO of one off India airlines over the weekend and he was more worried about his finance cost then engine maintenance cost so to speak. But he promised me to get some figures.

Technically speaking it's the start up of a turbine engine that puts wear an tear on it, and running hours. But the starting process is relatively speaking the hardest. Shutting down does't add to the wear and tear and process. But you are correct we count cycles.

its not about starting and shutting down.. its a lot of things. thrust usage for take off, thermal cooling etc

and barring fuel cost it is, one of the highest operating cost for an airline

Originally Posted by Jeroen

Noise abatement procedures around the globe call for idle thrust reverse. Shouldn't be a big thing at all. Especially for planes with auto braking. Autobrakes decelerate the plane at a specific deceleration rate. Irrespective of speed or weight of the plane. Applying reverse thrust while the autobrakes are at work will not slow the plane down quicker. The autobrakes keep it at the preset deceleration rate. But it does mean the brakes have to work less. So using reverse thrust in combination with auto braking increases brake componenet life and I suppose to some extend even tire wear as well.

At a low auto brake setting in theory, the reverse thrust could provide a higher deceleration rate than the autobrake system. In which case the brakes would not be working at all, so no wear and tear at all. Not sure if this is theory or whether it could happen in practice.

actually autobrakes work in conjunction with other devices like the thrust reversers and spoilers. so he amount of autobrake pressure reduces when reversers and spoilers are used. in other words the brakes will be working harder if reversers and spoilers are not deployed.

secondly in most airplanes its mandatory to use reverse thrust if auto brakes are selected.

[Jeroen]

Originally Posted by revtech

its called a tiller



Most commercial airliners have a device that stops rotation once airborne.



use of reverse thrust affects wear and tear of the engine !!



autobrake activation has go nothing to do with the nose wheel.. it starts when the main wheels touch the ground

Tiller, that's the word I was looking for!

Yes, probably on a lot of commercial airliner they will be brought to stop.That device is actually called brake! Usually on the main gear the brakes are applied gradually whilst the gear retracts As the wheels are freely spinning with no resistance you don't need much brake force to stop it. Just an automatic override of the ABS system. I believe most nose wheels are stopped simply by some sort of snubbing device. I.e. something that touches the tire.

I've heard several reason why the wheels gets stopped. Ranging from noise, gyroscopic effects and the possibility of a tire burst ripping through the various electrical and hydraulic lines in the wheel well.

I just don't know, I know very little about this part of (commercial) planes. Although I'm certified to fly a complex planes (plane with amongst others a retractable gear, I've only flown with retractable gear once.

On small planes you will usually find fixed gear. Their is an endless debate whether the additional weight for a retractable gear outweighs the performance gains on having less drag. Not relevant for commercial airliners of course.

Autobrakes have a complicated system of interlocking sequence. It starts with the throttle quadrant on which various mechanical locks are present. Then there is a host of other conditions that need to be met before the (auto)brakes engage.

Saying that it starts when the main wheels touch the ground is an oversimplification. For instance on the Airbus one of the other conditions is that the spoilers have deployed. On the Airbus, correct me if I'm wrong I don't think its the wheels touching the ground. Its actually the main gear strut compressing. Not sure if the tire speed as such is part of the interlocking sequence. Certainly airplane speed is! And yes, on some planes the nose gear comes into play on the interlocking sequence as well.

Just google Airbus 320 auto brake and you'll find a host of information that will give you an idea of the auto brake interlock sequence. And yes it will mention the spoiler deployment and yes you will find references to the nose gear oleo strut having to compress. Or try Prune, the professional pilot forum.

You also seem to be forgetting that the autobrake system is not only used during landing, but is also armed during take off on most planes. In order to assist during a Rejected Take Off. So you will appreciate that the interlocking needs to be a little more eloborate than just the main wheels touching the ground. During take off the wheels are touching the ground, but the autobrakes don't engage, but are armed to do so. Under those circumstances there are several other conditions that will activate the auto brakes. Could be as simple as the pilot pushing the RTO button, or pulling back the throttles into idle detent. Again, even with the auto brakes in armed mode, there are several interlocking conditions that need to be met before it engages. Speed, spoiler deployment a few other conditions spring to mind.

It is pretty complicated and the details confuse some of the pilots too. Have a look at this thread:

http://www.pprune.org/tech-log/51247...-aircraft.html
You can find many more examples and lots of interesting information on just about any (aviation related) topic on Prune.

So we have a jet engine that runs 14-16 hours a day. Most of that at pretty much well 90% thrust. On regional airliners they get started and shut down several times a day. And go from idle to max power several times a day during take off.

Why would a 15 second idle reverse thrust on top of that put any material wear and tear on it?? During reverse thrust nothing changes in the jet engine. It can't even tell it' is just idling or reverse thrust idling, other that parts of its either by-pass air or exhaust gets directed in a different direction?? If it puts wear and tear on the engine, why is it not measured as part of the maintenance cycle?

I really like to understand what it is that puts material wear and tear on a jet engine during (idle) reverse thrust. I just don't get it. Just an amateur trying to understand. Well, actually I do have a bit of professional experience with jet engines in marine applications, so do tell me. Always eager to learn more.

Jeroen

[revtech]

Originally Posted by Jeroen

Autobrakes have a complicated system of interlocking sequence. It starts with the throttle quadrant on which various mechanical locks are present. Then there is a host of other conditions that need to be met before the (auto)brakes engage.

Saying that it starts when the main wheels touch the ground is an oversimplification. For instance on the Airbus one of the other conditions is that the spoilers have deployed. On the Airbus, correct me if I'm wrong I don't think its the wheels touching the ground. Its actually the main gear strut compressing. Not sure if the tire speed as such is part of the interlocking sequence. Certainly airplane speed is! And yes, on some planes the nose gear comes into play on the interlocking sequence as well.

Just google Airbus 320 auto brake and you'll find a host of information that will give you an idea of the auto brake interlock sequence. And yes it will mention the spoiler deployment and yes you will find references to the nose gear oleo strut having to compress. Or try Prune, the professional pilot forum.

instead of trying to google.. i thought ill just refer to the Boeing FCOM

here is an extract,

"After landing, autobrake application begins when:
• both forward thrust levers are retarded to IDLE
• the main wheels spin–up."

Originally Posted by Jeroen

You also seem to be forgetting that the autobrake system is not only used during landing, but is also armed during take off on most planes. In order to assist during a Rejected Take Off. So you will appreciate that the interlocking needs to be a little more eloborate than just the main wheels touching the ground. During take off the wheels are touching the ground, but the autobrakes don't engage, but are armed to do so. Under those circumstances there are several other conditions that will activate the auto brakes. Could be as simple as the pilot pushing the RTO button, or pulling back the throttles into idle detent. Again, even with the auto brakes in armed mode, there are several interlocking conditions that need to be met before it engages. Speed, spoiler deployment a few other conditions spring to mind.

there is no RTO "button" , its a maneuver. which begins with thrust levers to idle and thats when the autobrakes engage only if the speed is higher than a pre-determined value.