Two 747 questions...

[atpcliff]

Landing in a Crab:
I wanted to practice landing the sim in gusty crosswind conditions, but our sims cannot do gusts. So, I asked for 50 kt direct crosswind with turbulence. The landing went OK. The guys doing my sim said that, since I crabbed into the wind, basically 100%, on touchdown in the real aircraft, my gear would have collapsed, as the side-loading was too high. I don't buy it.
Any problems with landing in a large crab angle due to high winds???

Best way to keep the brakes from overheating in a heavyweight 747-8 landing, long runway:
I think that Flaps 30, and Max Reverse are commonly accepted.
We were told minimal braking is best, so that means Autobrakes 2. But, an FO I was talking to said a DE told him that Autobrakes 4 is cooler, because the brakes are applied for a lessor time period, than Autobrakes 2. Another DE told me that AB3 is the best.

Any info, comments, etc. are gladly welcomed!
Namaste...

[atpcliff]

The brakes on the 747-8 are completely different than all the other 747 brakes. That is why one of our DEs said that the time the brakes are applied, is more critical than the intensity of the braking. According to another DE, the reps from the company said the mid-range breaking is better, but they didn't definitively tell us which is better: AB2, 3 or 4...

[Intruder]

I've flown the 747 Classic, 744, and 748. You can land the 747 (any model) in a crab. With a significant crosswind, it is almost mandatory. you cannot use more than 5 deg angle of bank, and you MUST have your velocity vector straight down the runway. Some pilots like to try to "kick out" the crab at the last moment, but just as often that will result in an overcorrection. On a wet runway, you'll hardly notice the airplane aligning itself with the runway; on a dry runway there will be significant shudder through the airframe as the tires scrub during the alignment.

I don't know what the difference is between 748 brakes and 744 brakes, other than capacity. Both have carbon brakes. I treated them the same. With the 748, always use Flaps 20 for T/O and Flaps 30 for landing, unless the airplane is VERY light (270T landing).

[Bergerie1]

I only flew the 747 Classic - what Intruder says about the max 5 degs of bank is correct, as also is the fact that it could be landed with the drift still on and, as he says, on a wet runway the 'self alignment' is hardly noticeable. But I still think it is better to remove the drift before touchdown. My only quibble is about kicking off the drift. Too many pilots talk about kicking off the drift when all that is needed is a gentle squeeze on the rudder. And in view of what Intruder says I would add that is better to remove too little drift than too much!

[742]

The Internet is full of videos of horrific 747 landings. No collapsed landing gear -- ever. The airplane can, and often does, land in a crab. However it is important to differentiate between landing in a crab with the airplane tracking the center-line and landing with sideways drift. The former is fine, the later is bad. In either case the landing gear will be OK, but don't expect any Christmas cards from tires 7,8,11 or 12 (body gear/aft) if you have a lot of sideways drift!

As for -8 brake energy, look it up in the QRH. You will find that reverse reduces brake energy on a heavy weight landing by 40ish%. You will also find that autobrakes 2 is "better" than autobrakes 4. So if you are concerned about brake energy on a -8 when landing near max landing weight, and you should be, your approach is correct. Full reverse, low auto-brake setting, flaps 30 -- in about that order.

And no, the brakes are not "completely different". They are the same technology as what are on the -400, just "new and improved". I suspect that we have the same employer, and part of the reason that the company is burning up -8 brakes are the loose cannons running around -- many of them in positions of authority.

[Intruder]

Best way to keep the brakes from overheating in a heavyweight 747-8 landing, long runway:
I think that Flaps 30, and Max Reverse are commonly accepted.
We were told minimal braking is best, so that means Autobrakes 2. But, an FO I was talking to said a DE told him that Autobrakes 4 is cooler, because the brakes are applied for a lessor time period, than Autobrakes 2. Another DE told me that AB3 is the best.That DE who said "Autobrakes 4 is cooler" needs to get his head examined. The harder the brakes are applied, the more power (i.e., energy dissipation/time) used and the less influence of other factors like air drag, reverse thrust, and mechanical friction. Therefore, Autobrakes 2 and max reverse thrust will cause the least wear.

Autobrakes 1 is not used in the 744/748 because it usually results in multiple brake-release cycles during the landing roll, which increase the wear on carbon brakes. Any time you think Autobrakes 1 might be sufficient (e.g., CVG Rwy 9), simply use idle reverse and Autobrakes OFF instead. On that runway, do a brake check crossing 18R/36L and roll to the end using hardly any brakes at all.

[atpcliff]

Thanx 4 all the replies, and all of the specific info and knowledge. I do get frustrated when I get three different sets of info that conflict, all from my own company, on how best to do things.
I would like to know if any carrier has a specific strategy they use to keep their -8 brakes less hot during landing.
We have had a lot of problems with the -8 brakes overheating...pretty much no problems on the -400.

[mustangsally]

Landing in a crab is no big deal. Looks a bit concerning from the flight deck, but when viewed fro the ground no big deal. Look at the Boeing and Airbus crosswind landing videos. No big deal, the aircraft will straighten it self out. I've landed at Prestwick with legal winds by the tower, but really very questionable. I've seen crabs held till touchdown and others with very slight wing low. but still in a crag, all worked well. About the worst was a rudder input just prior to touch down and the up wind wing lifting. Not a pretty sight. Watch the certification tapes of landing 777 and others with at least thirty knots at 90 degrees.

[742]

Thanx 4 all the replies, and all of the specific info and knowledge. I do get frustrated when I get three different sets of info that conflict, all from my own company, on how best to do things.
I would like to know if any carrier has a specific strategy they use to keep their -8 brakes less hot during landing.
We have had a lot of problems with the -8 brakes overheating...pretty much no problems on the -400.

If you work for who I think you do, go to the Training Center web site. 744/8 -> Training and reference material -> 747 Training Supplements -> Advisory Landing Distance 2016 -> This subject starts on page 17. IMO page 22 deserves special emphasis.

The entire presentation is excellent. Ignored by the rest of the Training Center, but excellent.

[742]

... According to another DE, the reps from the company said the mid-range breaking is better, but they didn't definitively tell us which is better: AB2, 3 or 4...

I am going to make a side comment on just this piece.

Having a few years of "office work" in another life, few things in aviation get my hackles up like "the rep from company X said....". These manufacturer rep positions are very, very low on the company food chain. Often entry level positions. Their job is to connect the airline's people with the manufacturer's people who can actually help. Their random opinion is often of little value, and having a bunch of instructors going out for beers with the wrong one of these guys can do a program a lot of damage.

My rule was that I would only act on what was in writing, on my desk. And virtually none of "the rep said....." ever made that transition.

The same thing with cold calling the manufacturer. The engineer who has the job of taking random calls from instructors and check airmen is going to be just above intern (management further up the airline food chain is a different matter).

In writing with accountability. Otherwise it is rumor, and often bad rumor.

Rant over.

[atpcliff]

If you work for who I think you do, go to the Training Center web site. 744/8 -> Training and reference material -> 747 Training Supplements -> Advisory Landing Distance 2016 -> This subject starts on page 17. IMO page 22 deserves special emphasis.

The entire presentation is excellent. Ignored by the rest of the Training Center, but excellent.

Thanx...will look at this...

[jimtx]

I've flown the 747 Classic, 744, and 748. You can land the 747 (any model) in a crab. With a significant crosswind, it is almost mandatory. you cannot use more than 5 deg angle of bank, and you MUST have your velocity vector straight down the runway. Some pilots like to try to "kick out" the crab at the last moment, but just as often that will result in an overcorrection. On a wet runway, you'll hardly notice the airplane aligning itself with the runway; on a dry runway there will be significant shudder through the airframe as the tires scrub during the alignment.

I don't know what the difference is between 748 brakes and 744 brakes, other than capacity. Both have carbon brakes. I treated them the same. With the 748, always use Flaps 20 for T/O and Flaps 30 for landing, unless the airplane is VERY light (270T landing).
Just to be clear, there is no rudder to kick out in the flare, there is a crab angle, in coordinated flight, which must be reduced to runway alignment using rudder for longitudinal correction while using aileron to keep the upwind wing from rising due to the yaw. This crosscontrol in the flare is also be called a slip. Any aileron input error should be to the excess which would put the upwind gear down earlier than the downwind. Some guys do that on purpose. I've seen more sideslip to landing sideloads on big jets caused by the guy who wants to fly it like a cub than sideloads by guys who did not decrab enough.
If your airplane does autoland read how it corrects for X-wind.
Even on aircraft designed to land in a crab, such as the T-38, most guys naturally gravitated to a decrab in the flare.

[Intruder]

Just to be clearer, you may use crab or slip or both on final in the 747. The autopilot will also use a combination with crosswinds over ~5 kts. So, you may indeed have some rudder input before the flare, especially if you had it coupled up until short final.

[jimtx]

It may be just a semantic point but crossed controls, a slip, should only be employed in the flare or just before it. My last airplane started alignment at 50 feet in autoland.

[Intruder]

In the 744 and 748 the alignment begins at 500' (200' if <5 deg crab angle is required) in an Autoland. So much for "just before the flare"...

[The Actuator]

That DE who said "Autobrakes 4 is cooler" needs to get his head examined. The harder the brakes are applied, the more power (i.e., energy dissipation/time) used and the less influence of other factors like air drag, reverse thrust, and mechanical friction. Therefore, Autobrakes 2 and max reverse thrust will cause the least wear.

Autobrakes 1 is not used in the 744/748 because it usually results in multiple brake-release cycles during the landing roll, which increase the wear on carbon brakes. Any time you think Autobrakes 1 might be sufficient (e.g., CVG Rwy 9), simply use idle reverse and Autobrakes OFF instead. On that runway, do a brake check crossing 18R/36L and roll to the end using hardly any brakes at all.
Is there a reference for the statement that AB1 will release the brakes multiple times? That is not my understanding of the AB system - in fact I believe that once the autobrake engages the pressure will modulate to keep the decelaration rate but will in fact not release entirely. The reason for this and also why, with Carbon brakes it is better to keep the brakes on is so that no oxidation occurs which results in an additional brake wear event apart from the shaving effect of the initial brake application. It is far better to have carbon brakes operating in the 200-300 degree range since the carbon will pack more tightly together resulting in less physical brake wear. Above 450 degrees the effect of oxidation really increases compared to lower temps and at temperatures lower than 200 the effect of shaving is greater given the strands of carbon are not tightly packed - almost like "standing up" as opposed to packed down when hot. I have been taught and so teach that AB is reccomended so that you have one continuous brake application - this gets the temps up to the 200 degree range rapidly and allows for minimal oxidation.

[felixthecat]

I think the point being made with AB1 is that the brakes are giving a rate of deceleration. If that rate of declaration is too low, for example with AB1, then you may not get the brakes heated up enough to get out of the low temperature range where most of the brake wear occurs, especially it your using reverse as well.

[torghabe]

atpcliff :The brakes on the 747-8 are completely different than all the other 747 brakes.
Sorry,what is the difference? Both of them multiple-disc carbon brakes. 747- Rotor and stator discs are made of carbon. 748- The multiple-disc carbon brakes. The carbon steel brake cables with a top layer of tin-coated zinc decrease friction and simplify maintenance.

[EDML]

There is a Boeing document out there about X-wind landings. It states that any Boeing commercial aircraft (excluding former MD) can be landed without decrab up to max. allowed X-wind component.

[stilton]

I have no doubt this is true


But in the case of the 767 with its forward
trailing main landing gear if you don’t have all the drift removed before touchdown it’s a
pretty abrupt impact !


Not forgiving and ive never been able to
understand how those side loads are
acceptable

[EDML]

I am pretty sure it is quite abrupt on a 747 as well. Seeing videos of such landings I always thought it would rip the tires of the wheel.

[RVF750]

As to abrupt. It's not rocket science...my 10p worth.

You have an approach speed and power, and a body angle to achieve the correct rate of descent. Just at the point you want to reduce R.O.D. with a flare, you apply significant sideslip to align, and wonder why the extra drag from this reduces your energy enough to make it plant on rather than kiss the tarmac? Pretty standard for all swept wing jet transports. By aligning a bit earlier you can ease up the power and reestablish an equilibrium. then when you flare and reduce power it bleeds energy more normally. Hence those that decrab earlier or after landing tend to suffer less "firm" arrival than the last minute swingers.....

[A Squared]

That DE who said "Autobrakes 4 is cooler" needs to get his head examined. The harder the brakes are applied, the more power (i.e., energy dissipation/time) used and the less influence of other factors like air drag, reverse thrust, and mechanical friction. Therefore, Autobrakes 2 and max reverse thrust will cause the least wear.


Not a 747 pilot, but this is my thought as well. You're going to bring the airplane to a compete stop before the end of the runway (hopefully) so the less braking you use the more of the planes kinetic energy is dissipated with drag and reverse. Dialing up your autobrake factor just means you use more brake, sooner, therefore less time for kinetic to be dissipated by drag and reverse, and more kinetic energy that is transformed into brake heat. At the extreme end of this is the runway long enough to stop using no brake and no energy is turned into brake heat.

[Local Variation]

Question.....I was down at LHR yesterday working and whilst walking down the Bath Rd noticed a 747 take off very close by on the northern runway westbound.

T’was a windy day like today and from my position on pretty much directly behind, could see the nose cranked into wind (to the left) on the initial climb out to maintain track.

The aircraft commenced a turn to right and I noticed the nose “appeared” to lag in the turn. Wondered whether the rudder would had been applied in the same aileron sense to kick the nose into the turn?

[mustangsally]

Suggest searching for Boeing Crosswind landing tests. They will demonstrate landing with at least 25Knts crosswind. Both from the flight deck and runway edge. Intruder has already said it all. I have landed with at least a 25 knot crosswind bit uncomfortable, but very controllable. The 74 all models are great.