[Jeroen]

Originally Posted by searchingheaven

Reverse thrust is used in the 777 during taxi as well due to the extremely powerful engines. Carbon brakes are efficient but using them constantly to keep the plane from accelerating wears them out. So we use reverse thrust at idle to essentially cut the available thrust to half.

Note that the use of reverse thrust above reverse idle is not recommended due to the possibility of foreign object damage and engine surge.

Interesting, the one thing with the carbon brakes is they are efficient, but they need to have reached their normal operating temperature to be that efficient. The wear of carbon brake is lowest when they are completely cold or at normal operating temperature. It's that bandwidth in between where wear could be higher than normal

Boeing and others recommends special braking techniques for carbon brakes:

http://www.boeing.com/commercial/aer...icle_05_1.html


https://airlinesafety.wordpress.com/...carbon-brakes/

Jeroen

[autobalan]

Great article, tons of information.
And sincere thanks for all the effort in compiling this.
Can i ask a doubt wrto to the engines, i am not sure of the particular model but it was a 777 of singapore airlines. During takeoff, i felt the push back to seat kind of power at the same time didn't experience this on A380.
Does 777 have this power feel in general or depends on model/type of engines?
OR am i completely wrong with my observation?

[Motard_Blr]

Thank you, SearchingHeaven for the creating this thread. I've enjoyed reading your original post and all the subsequent informative questions and answers.

Originally Posted by autobalan

Great article, tons of information.
And sincere thanks for all the effort in compiling this.
Can i ask a doubt wrto to the engines, i am not sure of the particular model but it was a 777 of singapore airlines. During takeoff, i felt the push back to seat kind of power at the same time didn't experience this on A380.
Does 777 have this power feel in general or depends on model/type of engines?
OR am i completely wrong with my observation?

I have had a similar experience on Emirates 777 and A380. The sensation of acceleration in an A380 was very light compared to a 777. I am curious to know the reason.

Thanks.

[searchingheaven]

Originally Posted by autobalan

Great article, tons of information.
And sincere thanks for all the effort in compiling this.

Can i ask a doubt wrto to the engines, i am not sure of the particular model but it was a 777 of singapore airlines. During takeoff, i felt the push back to seat kind of power at the same time didn't experience this on A380. Does 777 have this power feel in general or depends on model/type of engines?

Originally Posted by Motard_Blr

Thank you, SearchingHeavenfor the creating this thread. I am curious to know the reason.

Thanks.

The 777 feels faster due to three reasons.

1. The engines themselves are extremely powerful and provide a higher thrust-to-weight ratio of about 0.280 compared to the 0.225 of the A380 at maximum takeoff weight. Acceleration during the take-off roll is about the thrust to weight ratio. In general, all twins engined aircrafts must have a favourable thrust to MTOW ratio to overcome an engine failure after V1(i.e rejected take off impossible). Four engined aircrafts can work with a lower ratio.
   
   
2. The second and more important reason is that it is a very long range twin, but is used very frequently on shorter transcontinental routes as well. So a 777 on short routes is very lightly loaded and therefore accelerates faster.
   
   
3. The A380 itself is not like other big birds. It is slower than other large aircrafts. It approaches about 15 knots slower than a 777. This is due to the wing area which can generate enough lift even at lower speeds.
   
   
4. I am not a psychologist, but I think that the feeling of speed also depends on the noise level in the cabin. Since the 777 is definitely noisier than the A380, you guys might have felt the difference in speed to be a lot higher than it actually was.
   
   Glad that you guys liked the review.

[apachelongbow]

Originally Posted by searchingheaven

Reverse thrust is used in the 777 during taxi as well due to the extremely powerful engines. Carbon brakes are efficient but using them constantly to keep the plane from accelerating wears them out. So we use reverse thrust at idle to essentially cut the available thrust to half. Note that the use of reverse thrust above reverse idle is not recommended due to the possibility of foreign object damage and engine surge.

PS: I specifically remember seeing KLM 744s using single engine reverse thrust while taxiing at Schipol l when I was there 8 days ago.

Interesting!! Is there any concept of electric taxi in the Boeing? Airbus is just about to launch the electric taxi, where in electric motors within the main gear bogie, will run off the APU to ensure that taxi is via motor power. The aircraft can now reverse itself from the bay, taxi all the way to the holding point on APU and the engines can be started just before entering the runway (with sufficient warm up period), so that fuel burn during push back and taxi is on APU alone. It also very green, reducing sound pollution and a big plus for carbon credits...
Break wear will be almost non existent since the motors will reverse to reduce speed or decelerate, just like a electric locomotive. Taxi speed can also be preset via the MCDU to ensure the pilot operates only the tiller....

[Jeroen]

Originally Posted by apachelongbow

Interesting!! Is there any concept of electric taxi in the Boeing? Airbus is just about to launch the electric taxi, where in electric motors within the main gear bogie, will run off the APU to ensure that taxi is via motor power. The aircraft can now reverse itself from the bay, taxi all the way to the holding point on APU and the engines can be started just before entering the runway (with sufficient warm up period), so that fuel burn during push back and taxi is on APU alone. It also very green, reducing sound pollution and a big plus for carbon credits...
Break wear will be almost non existent since the motors will reverse to reduce speed or decelerate, just like a electric locomotive. Taxi speed can also be preset via the MCDU to ensure the pilot operates only the tiller....

Very interesting! Hadn't heard about it.
DC motors can develop a lot of torque and you are going to need a lot of torque to get a Boeing moving. Its going to take a lot of kit, motors, switch gear etc.

Im sure somebody has made a business case. But are they rally considering taxing on emotors all the way to the runway?

So i googled Boeing electric taxi. Quite a few hits as far back as early 2000.

But then a 2012 article says Boeing isn't pursuing this? Have they changed their mind since?

http://www.bloomberg.com/news/articles/2012-10-12/corvette-size-electric-motor-seen-changing-how-jets-taxi

Jeroen

[searchingheaven]

Originally Posted by apachelongbow

Interesting!! Is there any concept of electric taxi in the Boeing?

Boeing and Airbus both have been researching these systems for a long time. Boeing is going with Wheeltug® and Airbus is going with EGTS®. The difference is that Wheeltug® pulls the main gear while EGTS® pushes the main gear. Boeing isn't too interested in this. Their main argument is that if they wanted a dual-engine out taxi, they could just use tugs to position for takeoff which will be cheaper than fitting every aircraft with the gear, both from a complexity and weight POV. This tech is in a very early phase right now and nothing can be said about its future. Boeing will, in probability, drop it. A few questions that have been raised are:

1. First off, this will be used probably only on single aisle aircraft like the A320 and the B737. Will it have enough power to taxi the wide body heavies like the B777/A380. No.
   
   
2. Who's going to tell me about a fuel leak after engine start and other problems which I cannot monitor on the EICAS? An year ago I had a fuel leak on engine 2 and only knew about it from the ground crew who were monitoring the start.
   
   
3. The EGTS is a heat source. EGTS uses 50kw electric motors which will generate heat as the airplane taxis. All that heat is located inside the wheel. Brake hydraulic fluid has to stay below its flash point or there is a fire risk. So the EGTS will require some time to cool down and that is going to increase the holding time, since takeoff cannot be performed unless brakes have cooled sufficiently. EGTS hardware covers the axle-side of the wheel and hence blocks the cool holes in the flange of the wheel to permit the air pass through.
   
   
4. The warm-up period is another concern. High bypass engines require warm up prior to applying takeoff thrust and cool down prior to shutting down. If the engine has been shut down for several hours, it is desirable to operate at as low a thrust setting as practical for several minutes prior to takeoff. Add to that the wake turbulence separation after a 777 departs i.e 2 mins and we are looking at a 8 to 10 min delay at the holding point for the aircrafts holding behind you. At an airport like Atlanta, pilots would get down from their aircraft and beat you to pulp if you hold for this much time.
   
   
5. The weight of the motors will mean that the hydraulics that pull up the gear will have to be beefed up. That is going to add complexity.
   

[pgsagar]

Excellent thread. I'm aviationally challenged so it will take more than just one reading to grasp even 50 per cent of what's being discussed here. I have some questions though, which pilots might find funny. Please bear with me.

1. What is the take off and landing speed of an average airliner, say airbus A320? I was told 320 KPH. Is that true?

2. Why don't they double the runway length to minimise risk to take offs or landings. Pilots will then have the luxury of lengthened landings which would be smooth and it would take less toll on tires, landing gears, brakes and suspension. And no reverse thrust would need to be engaged which would mean no stress on airframe and fuselage.

Recently, while returning from Singapore to Kuala Lumpur, as the plane started to descend for landing at around 5 pm, I saw streaks running from both wingtips. It looked like aircraft jettisoned fuel. Why did they do that? It was a smaller plane. I think B737. Nothing seemed out of ordinary and landing was smooth, too.

[Jeroen]

Originally Posted by searchingheaven

[*]The weight of the motors will mean that the hydraulics that pull up the gear will have to be beefed up. That is going to add complexity.
T]

Interesting. As soon as you have to add weight to a plane, any plane, you also get a fuel penalty. You need to lug that extra weight around everywhere you go. So it always becomes a complex calculation, whether it makes sense on top of all the other challenges you already mentioned.

In the past there have been multiple studies and some trials on equipping landing gear with emoters to spin up the wheels prior to touchdown,thus reducing tire wear. A few prototypes flew around, but nobody could make that one a viable solution either. Similar complexity, although with much smaller e-motors obviously.

Jeroen

[searchingheaven]

Originally Posted by pgsagar

Excellent thread. I'm aviationally challenged so it will take more than just one reading to grasp even 50 per cent of what's being discussed here. I have some questions though, which pilots might find funny. Please bear with me.

1. What is the take off and landing speed of an average airliner, say airbus A320? I was told 320 KPH. Is that true?

2. Why don't they double the runway length to minimise risk to take offs or landings. Pilots will then have the luxury of lengthened landings which would be smooth and it would take less toll on tires, landing gears, brakes and suspension. And no reverse thrust would need to be engaged which would mean no stress on airframe and fuselage.

Recently, while returning from Singapore to Kuala Lumpur, as the plane started to descend for landing at around 5 pm, I saw streaks running from both wingtips. It looked like aircraft jettisoned fuel. Why did they do that? It was a smaller plane. I think B737. Nothing seemed out of ordinary and landing was smooth, too.

1. The correct landing speed for any jet varies depending on landing weight, flap selection and airport conditions. There isn’t a number we can give you that will always work. For the A320, the approach(landing) speed is generally 120-140 knots depending on the variables mentioned above. This translates to roughly 225-265 kph. So no, an A320 does not land at 320 kph.
   
   The B777 has approach speeds of 130-160 knots, again translating to 240-300 km/h.
   
   
2. The minimum runway required by an aircraft is calculated with a high safety margin. The FAR (Federal aviation regulation) takeoff field length is the longest of the following:
   
   • The distance required to accelerate with all engines, experience an engine failure 1 second prior to V1, continue the takeoff and reach a point 35 feet above the runway at V2 speed. (Accelerate-Go Distance).
     
   • The distance required to accelerate with all engines, experience an event 1 second prior to V1, recognize the event, initiate the stopping maneuver and stop within the confines of the runway (Accelerate-Stop Distance).
     
   • 1.15 times the all engine takeoff distance required to reach a point 35 feet above the runway.
   
   So runways need not be extended since aircrafts are designed with a high safety margin in mind.
   
   
3. As I discussed earlier, B737 or any narrow body aircraft does not have jettisoning capability since they can fly for 15 mins and have the required missed approach performance.(Please read this post for details: Link to post. ). What you saw was probably condensation trails.

[coolboy007]

Originally Posted by quickdraw

Lastly, maybe Coolboy007 can answer, has airbus changed anything inside their cockpit to give better visual indication of current stick input and which stick has requested priority?

No, Airbus has not changed any thing in this regard but believe me that there is nothing wrong with the side stick design. If none of the pilots have taken priority with the priority button pressed and both start acting on the stick, there is a loud "Dual Input" warning and the dual input warning comes on the glare shield which is right in your face and impossible to ignore.

Any of the pilot can take priority and keep the red button pressed for 40 seconds, a red light comes on the glare shield of the pilot who has his stick deactivated and a green light in front of the pilot who has priority. The pilot with the deactivated stick can always take priority back again by pressing his priority button. If both pilots press it at the same time, the one who presses last has priority.

The cockpit and systems are not designed to ensure that pilots dont start fighting for controls. In any urgent situation like a stall, windshear or a tcas (traffic collision avoidance system) - the pilot flying reinforces his controls and loudly says "Tcas, i have controls" or "Stall, i have controls". The other pilot now has to monitor and not start fighting for controls.

Even in a Boeing, it is impossible to manage the situation if both pilots start fighting for controls unless you punch the other guy in the face.

The only thing wrong with Airbus side stick design in my opinion is that the pilot non flying will never know what pilot flying is doing with his stick (unless you look at your instruments) as the side sticks are not linked and do not move together. For AF447 - the junior co pilot kept his stick full back in a stall, there were 50-60 stall warnings, tons of dual input warnings but the crew ignored every thing. The senior co pilot could have taken controls with the priority as soon as they entered in a stall situation, the flight did face issue with pilot tubes icing and there was no valid airspeed indication, the auto pilot tripped off to hand over the controls back to pilot, the a/c entered into alternate law where there are no airbus fbw protections, it was just like a Boeing 737 now with the failure of airspeed indications, af447 did not have to end that way.

Once you entered into a stall with commercial airlines, you need 4000-6000 feet easily to come out. We practiced a stall in the 320 today (on the sim) and the aircraft fell 4000 feet before it recovered, i had to pitch down when the stall warning sounded, this is basic training, you never pitch up.

The problem these days is that there is so much automation that pilots are forgetting to fly manually and how to handle the aircraft when the auto pilot trips off. There was an accident recently in US with a 777 doing an ILS approach, the glide slope at airport was inoperative providing vertical guidance and only localizer was working (lateral guidance), the crew was informed about it but the aircraft crashed. The commander later said that he had not hand flown an approach without vertical guidance for so long that it became impossible for him to do it, this seems impossible in clear weather but then people always blame pilots, you need to blame the airline's training department too. This ILS approach without vertical guidance was taught to us in our second session of training and it is very simple but if you do not practice it for 10-11 months, you are bound to make mistakes, there is a reason that all pilots have sim checks every 6 months.

This is why I love Boeing, so captain I'm putting my trust in you. Get me home safe.

- you are one of those who believe, "if it is not a Boeing, i am not going". The safety records of Airbus are as good as Boeing and both companies make great airplanes.

[Jeroen]

Originally Posted by coolboy007

There was an accident recently in US with a 777 doing an ILS approach, the glide slope at airport was inoperative providing vertical guidance and only localizer was working (lateral guidance), the crew was informed about it but the aircraft crashed. The commander later said that he had not hand flown an approach without vertical guidance for so long that it became impossible for him to do it, .

I assume you are referring to Asiana 214 at Los Angeles?

In addition to the captain not having much hand flown lately, there was also confusion/misunderstanding on the flightdeck on what was to be expected from changing the vertical mode to FLCH SPD. (see our earlier discussion about vertical modes)

Here is an interesting synopsis:

http://www.ntsb.gov/news/events/Page...-Abstract.aspx

To my earlier point, there is no simple correlation between hours flown and accidents. This was a very seasoned cockpit crew, with even the pilot monitoring a seasoned 777 captain himself overseeing/supervising the captain flying as part of his training/familiarisation.

At first it seems just inconceivable that any reasonable experienced pilot make these sort of mistakes. It's almost as if there is rookie in control.

But when you read the synopsis and the recommendation you also begin to understand how complex these things. From system design, in depth understanding of the system operations, sufficient hand flying, etc etc.

The report mentions that at 500 ft above airport elevation Asia company procedure dictated the plane needs to be in stable approach and all crew members either failed to notice it wasn't or did not call it out. At this point in time all they had to do was initiate a go around and none of this would have happened.

The report doesn't mention it, but many aviation experts do feel that pilots are sometime reluctant to initiate a go around for all the wrong reasons. It has been suggested many times that in particular Asian Culture have a profound negative effect on effective Crew Resource Management (CRM).

Hence, nobody called out the need to Go Around (too much hierarchy?), nobody wanted to do a GO Around (loose face?)

Jeroen


Jeroen

[apachelongbow]

Originally Posted by Jeroen

I assume you are referring to Asiana 214 at Los Angeles?


The report mentions that at 500 ft above airport elevation Asia company procedure dictated the plane needs to be in stable approach and all crew members either failed to notice it wasn't or did not call it out. At this point in time all they had to do was initiate a go around and none of this would have happened.

The report doesn't mention it, but many aviation experts do feel that pilots are sometime reluctant to initiate a go around for all the wrong reasons. It has been suggested many times that in particular Asian Culture have a profound negative effect on effective Crew Resource Management (CRM).

Hence, nobody called out the need to Go Around (too much hierarchy?), nobody wanted to do a GO Around (loose face?)

I agree!! A go around in this case was mandatory. However Ariana airlines in particular and the home country in general have a concept of strict hierarchy and something called loss of face. Due this, the junior never ever questions or corrects the senior, even if they are running into the ground. Also they had a dangerous situation where in the pilot flying was a senior captain who had recently graduated to the type: 777, the co pilot too was a captain and the guy in the jump seat was a senior instructor, if I am recollecting correctly. With multiple commanders in the cockpit, it is a recipe for errors, because one is reluctant to challenge and correct someone equal of rank or senior, that's why Indian DGCA frowns at rostering two captains together for a flight unless of severe copilot shortage.
Secondly the crew had flown all night, were landing visual on a runway, early morning, into the sun, because the runway had notams on approach aids, all this coupled together created the perfect storm so to speak...

[honeybee]

A newbie question. I love to watch aeroplanes (airplanes!), and sometimes I watch on youtube different videos of planes landing in severe crosswinds (crab-like).

What are the airports or places where you see such high crosswinds? Mind you, these aren't small airplanes like the Cessna, but sometimes big jets too. Also in order to be able to land successfully do you guys need to train for it? Are there any additional certifications to acquire before a pilot can fly to such airports, or is it part of the basic training?

Just out of sheer curiousity, what is most likely to fail during a landing? I am assuming take offs are relatively safer than landings with a lesser number of things likely to go wrong, whereas during landing, the chances of various things going wrong would be higher. So out of all components required to make a safe landing, what are the things more likely to fail - maybe in terms of previous statistics? And what is the most critical part that MUST work for a safe landing?

[souvik6]

Originally Posted by honeybee

A newbie question. I love to watch aeroplanes (airplanes!), and sometimes I watch on Youtube different videos of planes landing in severe crosswinds (crab-like).

What are the airports or places where you see such high crosswinds? Mind you, these aren't small airplanes like the Cessna, but sometimes big jets too. Also in order to be able to land successfully do you guys need to train for it? Are there any additional certifications to acquire before a pilot can fly to such airports, or is it part of the basic training?

Just out of sheer curiousity, what is most likely to fail during a landing? I am assuming take offs are relatively safer than landings with a lesser number of things likely to go wrong, whereas during landing, the chances of various things going wrong would be higher. So out of all components required to make a safe landing, what are the things more likely to fail - maybe in terms of previous statistics? And what is the most critical part that MUST work for a safe landing?

Excellent thread with tons of first hand info from professionals and enthusiasts!

Regarding landings in severe cross wind conditions I would recommend to check out youtube videos at Birmingham airport as it is famous for sudden change in wind direction at one of its runways..

It is just so exciting to watch planes landing against severe crosswind and that exact moment when the pilot kicks the rudder pedal at the last moment before impact to align the plane with runway..do check it out as it is supposedly one of the most exciting and favorite maneuver of pilots