[Strella]

Originally Posted by audioholic

I recall reading somewhere that in Airbus aircraft the autobrake levels are set for required deceleration and depending upon the situation and external factors the brakes are used. Is it the same in Boeing? What is the meaning of the levels 1, 2, and so on?

Autobrake 1, 2, 3, Autobrake Max, and Maximum manual braking are the desired deceleration rates of braking on the some of the Boeing aircrafts used for landing.

Autobrake 1 is mild braking, usually used when runways are long and not limiting, Autobrake 2 is a little more stronger braking compared to Autobrake 1 and is also used usually when the LDA ( landing distance available is more than 7000 feet) and Autobrake 3 is advised for LDA less than 7000 feet. This example is for Boeing 737 NG aircraft.

The biggest advantage of Auto Braking is that it is it is applied immediately on landing and also it is absolutely symmetrical braking.( Unlike cars, there are 2 independent brake peddles, one on top of each rudder pedal and hence if the pilot is not careful he could apply different braking on both the main wheels. Nose wheel has no brakes).

Hope it helps.

[Jeroen]

Originally Posted by Strella

Unlike cars, there are 2 independent brake peddles, one on top of each rudder pedal and hence if the pilot is not careful he could apply different braking on both the main wheels. N.

To add, on smaller planes, such as the ones I fly, you use this to actually steer the plane. Quite a few of these planes don’t have nose wheel steering but rely on a castoring nose wheel and differential braking to steer.

All planes have the ability to use differential braking. On large commercial planes it might be used to assist on very tight turns. Obviously, on landing you want to have as symmetrical braking as possible, but during taxi-ing it might be different.

The heaviest use of the braking system is during a so called Rejected Take Off or RTO. On large airplanes as the 777 it’s also the auto braking system that kicks in.

There are certain conditions that need to be met, certain speed (above 80 knots or thereabouts), but when the pilots closes the throttles the auto brake system kicks in automatically to bring the plane to a full stop. On take off the plane is at it heaviest. Much heavier then on landing!

Each plane as part of its certification needs to go through a RTO test. Have a look at this, its quite spectacular:

https://www.youtube.com/watch?v=f4LFErD-yls

Jeroen

[Jeroen]

Nice video about the 777, enjoy
Jeroen

https://www.youtube.com/watch?v=axQ0...ature=youtu.be

[audioholic]

Had a chance to travel on the upper deck of the Emirates A380 from Dubai to Frankfurt. Oh man, what a place to be in. This was the first time I traveled in the upper deck business class, compared to the business class on the 777 which I had earlier traveled in. Absolutely silent, smooth and rarely felt a thing. Leave the economics part, but the A380 is really something unique an offering. Just hope the aircraft sees more patronage and orders and doesnt fade away in history as a white elephant, which no doubt it is.

[Jeroen]

Originally Posted by audioholic

Had a chance to travel on the upper deck of the Emirates A380 from Dubai to Frankfurt. Oh man, what a place to be in. This was the first time I traveled in the upper deck business class, compared to the business class on the 777 which I had earlier traveled in. Absolutely silent, smooth and rarely felt a thing.

Agree, the upper deck of an A380 is the place to be on long haul, nothing compares!

Jeroen

[sriramr9]

Originally Posted by Jeroen

Feel free to ask your questions, I’m sure you will get an answer. There are several professional pilots on Team-BHP.

Hello Jeroen, With respect to the landing speed and approach, despite having multi bogie wheel sets and a smooth tarmac below why does one experience the landing with a lot of small vibrations/jolts horizontally and vertically giving the passenger seated, an experience as though the wheels are subjected to roll over some uneven, broken patchy tarmac which is really not the case,

What causes such vibes despite the landing gear is of highest quality replete with complete shock absorbing equipment's, best rubber rolling over smooth concrete surface ?

[Jeroen]

Originally Posted by sriramr9

Hello Jeroen, With respect to the landing speed and approach, despite having multi bogie wheel sets and a smooth tarmac below why does one experience the landing with a lot of small vibrations/jolts horizontally and vertically giving the passenger seated, an experience as though the wheels are subjected to roll over some uneven, broken patchy tarmac which is really not the case,

What causes such vibes despite the landing gear is of highest quality replete with complete shock absorbing equipment's, best rubber rolling over smooth concrete surface ?

Really more a question for Searchinghaven as he flies these wide bodies, but I’ll take a stab at it:

Not sure how many landings you have experienced, but it is possible to get a very smooth landing, with very little vibrations and jolts. But admittedly that is under pretty ideal conditions. There are also other considerations why a pilot might to want to put the plane pretty firmly on the ground.

When an airplane lands it goes from flying in the air to rolling out on the runway on its wheels. During that transition the plane might not be fully aligned with the runway centre line, especially with crosswinds. But as soon as the gear touches the runway it will start exerting forces on the airframe. Also, depends a bit on the plane at hand, but in general as soon as the main gear touches the ground fully the spoilers are (automatically) deployed. This will dump most of the lift the wing was developing, so additional load is put on the landing gear. At the same time the airframe might be yawning (see above) and pitching (nose coming down) etc.

As soon as the first wheel hits the ground it starts spinning up very rapidly and the same goes for all other wheels. Again, this causes stress on the gear, noise, vibration etc.

So although perfectly in control there are a lot of different forces at work in the space of literally a few seconds from that moment the gear starts to touch the runway and the plane is fully settled on the runway and decelerating.

Not a 777, but this video gives you some idea what all these different forces do.

https://www.youtube.com/watch?v=nlzsYkmwtOc

And here a slo-mo for the 777 Notice how the right gear is fully down before the left one. Nothing unusual, but it will cause some rumbling, vibration due to different stresses on the gear and air frame//

https://www.youtube.com/watch?v=e3rI_UsKbBw

Jeroen

[Thad E Ginathom]

Originally Posted by Jeroen

... But as soon as the gear touches the runway it will start exerting forces on the airframe. Also, depends a bit on the plane at hand, but in general as soon as the main gear touches the ground fully the spoilers are (automatically) deployed. This will dump most of the lift the wing was developing ...

Watching that, I'm surprised at the steep angle to the ground as the rear wheels make contact --- and how the pilot brings the nose gently to the ground!

[Sail]

After viewing both the videos, I thing rear set of wheels (of the complete bunch of two/three sets line up) always wear-off faster than remaining wheels ? (as they take the maximum pounding while touch-down and continue for some distance till the time all the sets shares weight)

[searchingheaven]

Sorry guys for being absent from this forum since a long time. Was caught up with some family issues. So before I answer specific questions, a small primer on brakes and auto brakes system used in the 777.

Originally Posted by audioholic

What is the meaning of the levels 1, 2, and so on?

First off, brakes are the primary devices which slow down an aircraft. Spoilers and reverse thrust are intended not to slow the aircraft, but to disrupt lift and put the weight on the wheels where the brakes can be more effective. Hence, reverse thrust and aerodynamic braking from spoilers aren't considered when calculating landing distance. Wheel brakes are.

With that out of the way, let's talk about something called Deceleration Rate. Deceleration rates are measured in knots per second. Autobrakes provide a known rate of acceleration, which means that it can be used to calculate stopping distance. In our own calculations, the Landing Data card cites the specific stopping distance with each level of braking applied; these distances don't change with or without reverse thrust, but the brake energy and subsequent brake temperature certainly does. If the calculation states that a medium autobrake setting will provide 6,000' of landing distance, then it provides it at the medium setting with or without the reverse thrust. With reverse thrust, the distance remains the same, but the brakes are cooler because the autobrake system uses the brakes less.Also, as the aircraft decelerates, the autobrake system will decrease braking pressure.

There are 5 levels of auto-braking in the 777.

• A/B 1-------4 kts/s------Most gentle out of the 4. Good for long runways.
• A/B 2-------5 kts/s------Most common setting for 777's landing in normal conditions.
• A/B 3-------6 kts/s------THis is where things start to tighten up a bit. Shaves off around 1500-2000 ft landing distance compared to A/B 1 in typical conditions.
• A/B 4-------7 kts/s------At A/B 4, the deceleration can catch you off-guard if you're not prepared for it. Nose dives brutally. We use these for KJFK's 04R, around 8000 ft LDA.
• A/B Max AUTO----11 kts/s----- Newcastle airport. LA 7500 ft. At MAX Auto, it really is savage. We stopped within 4000 ft in slightly slippery conditions.
• A/B RTO----RTO stands for Rejected take-off. This mode is armed before taking off and kicks in if and when a take-off roll is aborted. Never had to use it fortunately, apart from the sim.

Originally Posted by Rehaan

How come you use the close-to-max braking on slippery runways? I'd imagine it would be the other way around...

As explained, the anti-skid is active at all times. A higher autobrake setting just provides a faster deceleration rate. And for slippery runways, we obviously use a higher A/B.

Originally Posted by sriramr9

What causes such vibes despite the landing gear is of highest quality replete with complete shock absorbing equipment's, best rubber rolling over smooth concrete surface ?

Originally Posted by Jeroen

Not sure how many landings you have experienced, but it is possible to get a very smooth landing, with very little vibrations and jolts. But admittedly that is under pretty ideal conditions. There are also other considerations why a pilot might to want to put the plane pretty firmly on the ground.

When an airplane lands it goes from flying in the air to rolling out on the runway on its wheels. During that transition the plane might not be fully aligned with the runway centre line, especially with crosswinds. But as soon as the gear touches the runway it will start exerting forces on the airframe. Also, depends a bit on the plane at hand, but in general as soon as the main gear touches the ground fully the spoilers are (automatically) deployed. This will dump most of the lift the wing was developing, so additional load is put on the landing gear. At the same time the airframe might be yawning (see above) and pitching (nose coming down) etc.

As soon as the first wheel hits the ground it starts spinning up very rapidly and the same goes for all other wheels. Again, this causes stress on the gear, noise, vibration etc.

So although perfectly in control there are a lot of different forces at work in the space of literally a few seconds from that moment the gear starts to touch the runway and the plane is fully settled on the runway and decelerating.

Jeroes sir has summed in a much better way than I ever could.

Originally Posted by Sail

After viewing both the videos, I think rear set of wheels (of the complete bunch of two/three sets line up) always wear-off faster than remaining wheels ? (as they take the maximum pounding while touch-down and continue for some distance till the time all the sets shares weight)

No, in fact it's just the opposite. The main tires tend to last longer than the nosewheel tires. The nosewheel wears out first because it has more weight bearing and on some aircraft is a smaller diameter tire. The nosewheel typically only has two tires while the main wheels have a minimum of 4 (2 per bogie, 2 bogies minimum), some aircraft have even more. The Boeing 777 has two bogies for the main wheels with 6 tires each. That's 12 tires vs 2.

[sriramr9]

Thanks and shout outs to Jeroen and SearchingHeaven and many pilots here for enlightening us with a plethora of facts,figures, technology about aviation which is in context here and for sharing with us all that critical knowledge, experience and real life episodes in a platter to a layman's living room, i cannot be more thankful.

To come back to thread, please check and let us know your view on the supersonic air travel fever picking up yet again.

http://www.theverge.com/2016/11/15/1...nveil-concorde

[Jeroen]

Originally Posted by sriramr9

To come back to thread, please check and let us know your view on the supersonic air travel fever picking up yet again.

]

With the retirement of Concorde we have see a long string of various initiatives all claiming to bring back supersonic air travel for the masses.

It will be nice when it happens, but I'm not holding my breath.

One of the big problems of Concorde was the legislation and getting permission to operate in somebodies airspace at Mach 2 because of noise problems. I don't hear much about this part of the challenge. Must be many more!
Jeroen

Jeroen

[TKMCE]

Apologies if this has been posted earlier.

The following link in the Federal Aviation Administration website details and discusses a number of major accidents of transport aircraft in the last 50 years.

http://lessonslearned.faa.gov/ll_mai...=71&LLTypeID=3

These pages also gives a link (I think the only publicly available one) to the accident report of IC 605, the A320 which crashed at Bangalore on February 1990.

Many of these accidents were featured in the "Air Crash Investigation" series shown on the National Geographic Channel.

[MinivanDriver]

One promising technology improvement that is already happening is the ability of turbo fan engines to operate at (low at present) supersonic speeds. The Concorde consumed a lot of fuel as it used turbo jet engines.
This would be a key in making supersonic air travel more viable. I have a feeling the first transport category variants will have low supersonic speeds (Mach 1.6 or thereabouts). Boeing sort of toyed with the idea in the form of its sonic cruiser a decade or so back and then shelved it. However with the improvements in technology ( engines & sonic boom reduction), they could potentially bring it back if there is enough market demand.

Originally Posted by Jeroen

With the retirement of Concorde we have see a long string of various initiatives all claiming to bring back supersonic air travel for the masses.

It will be nice when it happens, but I'm not holding my breath.

One of the big problems of Concorde was the legislation and getting permission to operate in somebodies airspace at Mach 2 because of noise problems. I don't hear much about this part of the challenge. Must be many more!
Jeroen

Jeroen

[Jeroen]

Originally Posted by MinivanDriver

One promising technology improvement that is already happening is the ability of turbo fan engines to operate at (low at present) supersonic speeds. The Concorde consumed a lot of fuel as it used turbo jet engines.
This would be a key in making supersonic air travel more viable. I have a feeling the first transport category variants will have low supersonic speeds (Mach 1.6 or thereabouts). Boeing sort of toyed with the idea in the form of its sonic cruiser a decade or so back and then shelved it. However with the improvements in technology ( engines & sonic boom reduction), they could potentially bring it back if there is enough market demand.

I really don’t know much about whether turbo fan engines could operate at supersonic speeds. Today they can’t, and as far as I know anything like a propellor blades approaching speed of sound will run into problems, flutter springs to mind. As far as I know fans work best/most efficient in the subsonic regime. So even if they would not break, I’m not sure how much good they would be going supersonic. But then again, I really don’t know. Just note, that the when talking about sub/supersonic speed I’m referring to the air near the propellor blade which could be considerably different from the speed of the plane.

The Concorde engines were extremely advanced for their time. The intake air was slowed down to subsonic speeds, as jet engines don’t do well on supersonic intake air either.

What set Concorde aside from every other supersonic aircraft is that it flew at Mach 2 without the use of superheat/afterburner. That gave it is range and endurance.

Although research in reducing sonic boom has continued I’m not sure how far they are these days in term of applying something in practice. It all comes down to the shape of the fuselage, wings and engines. Nothing has changed from Concorde’ days in that respect!

http://machinedesign.com/defense/sup...ing-sonic-boom