20 replies to this topic

[clum]

Was listening to Heathrow director last night and noticed an Emirates 380 that went missed approach due to a flap problem. They took up the hold at LAM for 20ish minutes before making another approach. They advised that they had no flap control so would be making a flaps up landing and would be requiring a brake inspection after landing as their APP Vref would be in excess of 162kts.

That struck me as really not all that fast given that no flaps were being used? What's a typical landing speed for one of these aircraft? I suppose it is probably slower than something like a 744 given the sheer size of the 380's wings but I would have expected something more in the region of 180-200kts with zero flaps. I remember that the Air Transat A330 that ran out of fuel made a flaps up landing at 200kts. Obviously better to be faster in that scenario given no margin for error.

Aircraft landed without any further issue. Actually didn't even require full length of 27L to stop, managing to comfortably vacate at N7 is I remember correctly. Must be some stopping power in those brakes!

Edited by clum, 22 October 2010 - 03:31 AM.

[Janu]

Oops, I'm flying on one of their A380's in three days time! :/

[pyruvate]

Janu, on Oct 22 2010, 03:20 PM, said:

Oops, I'm flying on one of their A380's in three days time! :/

Exactly what I thought when I saw the last reply was by you


But this is interesting, what was the actual problem?  Airbus say anything yet?

[clum]

I've not heard anything further about it. Don't really consider it any sort of major problem as it wasn't treated as an emergency at all other than a quick brake/runway inspection after landing. Might get more details on PPRUNE at some point, but doubt it will make the media in any capacity.

[higgi1fc]

Well, not claiming to be an Airbus expert by any means, but one reason could be that they may have been able to get the slats extended, but not the flaps.  In big airplanes, slats tend to make more of a difference in approach speeds than flaps do.  For example, in the 10:

Picking a gross weight of 300,000lbs (you'd obviously reduce to min practical in a case like this)

35/EXT Threshold speed (with slats, and 35 flaps--NORMAL):  131kts
0/EXT Threshold speed (with slats, but no flaps):  152kts
0/RET Threshold speed (no slats, no flaps): 188kts

Thats a difference of over 30 knots just for not having slats!

Then you compare it to

0/EXT Threshold speed (with slats, but no flaps):  152kts
22/RET Threshold speed (no slats, but 22* flaps):  177kts

That shows that with no flaps, but with slats, your threshold speed is more than 20 knots slower than if you had flaps but no slats.

Again, this is for a completely different airplane, but I would think the principle would be the same and MIGHT explain the "slower" approach speed.  (And our numbers are fudged slightly from the normal DC-10 because of the boom)  Something else they would have to take into account in a situation like this is the tire speed limitation.  For us, it is 204kts (groundspeed), so anything in excess of that you'd be taking the chance of blowing out the tires, not from too much brake energy, but from speed alone.  You'd definitely want to reduce gross weight as much as practical to get an approach speed below this.

[clum]

Cheers, had thought slats might be a factor but didn't know it would have made such a drastic difference.

[Cactus]

160 is around normal for flaps-up with most commercial airliners.

The 200 kts on the Air Transat flight was simply because going-around wasn't an option. And of course, every single axle and tire assembly on that airplane had to be replaced.

[_NW_]

clum, on Oct 22 2010, 03:25 AM, said:

Aircraft landed without any further issue. Actually didn't even require full length of 27L to stop, managing to comfortably vacate at N7 is I remember correctly. Must be some stopping power in those brakes!

Brakes are the primary stopping force of any aircraft..   about 85% of the stopping power comes from brakes.  Also keep in mind, the A380 only 2 thrust reversers.  The inner two engines don't have them.

[Fourtyfreak]

Domo, on Oct 22 2010, 02:43 PM, said:

Brakes are the primary stopping force of any aircraft..   about 85% of the stopping power comes from brakes.  Also keep in mind, the A380 only 2 thrust reversers.  The inner two engines don't have them.

You sure it's not the outboard engines that don't have them? Don't want to get debris in the outer engines as they overhang the runway.

I also believe that the original plan was to not fit thrust reversers at all. The brakes really are that good nowadays.

Paul

[pyruvate]

Fourtyfreak, on Oct 22 2010, 07:28 PM, said:

You sure it's not the outboard engines that don't have them? Don't want to get debris in the outer engines as they overhang the runway.

I also believe that the original plan was to not fit thrust reversers at all. The brakes really are that good nowadays.

Paul

I think that putting the Reversers on the outer engines would have a greater effect than putting it on the inner ones because of moment, but I don't know how much moment would play a role.

And yea, the original plan was to not fit reversers at all, but they wouldn't be approved without them.

[_NW_]

Fourtyfreak, on Oct 22 2010, 08:58 AM, said:

You sure it's not the outboard engines that don't have them? Don't want to get debris in the outer engines as they overhang the runway.

I also believe that the original plan was to not fit thrust reversers at all. The brakes really are that good nowadays.

Paul

YOu know, I honestly can't remember..  I know only 2 of them have it though.

ANd yes, brake technology has improved..  most large airliners have already switched to composites and ceramics rather than the older style brakes which head up and fade (and catch on fire at a lower temperature)...

[Mohammad]

You'd think it won't stop that easily, given its sheer size and all.

[Tako]

pyruvate, on Oct 22 2010, 10:11 AM, said:

I think that putting the Reversers on the outer engines would have a greater effect than putting it on the inner ones because of moment, but I don't know how much moment would play a role.

And yea, the original plan was to not fit reversers at all, but they wouldn't be approved without them.

I'm pretty sure they were more concerned with FOD than effectiveness. That said, aircraft have to be able to stop on a runway without the use of thrust reverser as per regulations.

Does the moment play a role at all? With control surfaces, they become increasingly effective as you move outward, but I'm not sure the placement of the engines has anything to do with their effectiveness on rollout.

[clum]

Domo, on Oct 22 2010, 08:43 AM, said:

Brakes are the primary stopping force of any aircraft..   about 85% of the stopping power comes from brakes.  Also keep in mind, the A380 only 2 thrust reversers.  The inner two engines don't have them.

I know, that's why I said it

[Flying_Pie]

Moment doesn't play a role in reverse thrusters because they're not applying torque, they're just applying a backward force. If they wanted to turn using the reverse thrusters then moment would play a role (same reason ailerons apply more torque if they're closer to the wingtips), but since they're applying a symmetrical force and there's no net torque, moment doesn't affect stopping distance.

Although, moment may be considered for the engineers in this case because the engines are applying a torque to the individual wings, and therefore more moment = more torque = more stress. But that's completely unrelated to the topic.

[divemaster08]

Its the 2 inner engines on the A380 that have reverse thrust.  

The Outer ones do not due to the fact that they can be at certain fields over the edge of the runway and would cause perhaps FOD to be thrown out and then sucked into the engines or cover the runway with FOD behind them.

[FL050]

Fourtyfreak, on Oct 22 2010, 08:58 AM, said:

You sure it's not the outboard engines that don't have them? Don't want to get debris in the outer engines as they overhang the runway.

I also believe that the original plan was to not fit thrust reversers at all. The brakes really are that good nowadays.

Paul

Brakes have been that good for decades, they are just insanely expensive to replace; that is why a lot of pilots try to utilize the brakes as little as possible.

For example, on the King Air 200 that I fly the brake pads alone are about $2,500; not including installation.  Thankfully you don't need brakes for practically anything in a BE-20.  I can't imagine what that would cost on commercial airliners.

Edited by FL050, 22 October 2010 - 01:18 PM.

[Flying_Pie]

FL050, on Oct 22 2010, 12:18 PM, said:

Brakes have been that good for decades, they are just insanely expensive to replace; that is why a lot of pilots try to utilize the brakes as little as possible.

I read something on PPRune awhile back stating SWA's pilots are prohibited to use brakes above 80 knots to preserve them and reduce brake cool-down time (therefore enabling quick turnarounds).

Somewhat interesting

[higgi1fc]

Flying_Pie, on Oct 22 2010, 02:21 PM, said:

I read something on PPRune awhile back stating SWA's pilots are prohibited to use brakes above 80 knots to preserve them and reduce brake cool-down time (therefore enabling quick turnarounds).

Somewhat interesting

I'm just sayin'!  lol




(and yes, i know this is not the reason for either of those incidents...just an attempt at humor)

[clum]

Haha well played.