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B777 single engine overweight landing question.

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B777 single engine overweight landing question.

Old 24th Feb 2019, 12:56
  #21 (permalink)  

Only half a speed-brake
 
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I think the message of the article is quite clear.
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Old 24th Feb 2019, 13:27
  #22 (permalink)  
 
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Originally Posted by dixi188 View Post
Overweight landing only when you have no time to dump!
Why cook the brakes and tyres?
please substantiate this reply .

The triple is capable of landing overweight , single engine , and that does not mean the brakes will be , as you so describe cooked. Equally capable of a cat III B approach and landing with one Donk .
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Old 24th Feb 2019, 13:34
  #23 (permalink)  
 
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Originally Posted by B2N2 View Post
Dump the fuel and land below max weight.

Why?
Back it up ol boy.

What is the the reason the donk failed. What do you do when the second fails - while dumping - while you send your beloved Acars to your ops .

Do you not brief these type of scenarios before take off.
Are you familiar with your AFM.

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Old 24th Feb 2019, 21:37
  #24 (permalink)  
 
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Agree.
If I am sitting down the back with my family I’d rather you didn’t climb up and fly off somewhere remote to spend 45 minutes dumping fuel on one engine if the aircraft has the ability to land immediately with ample performance margins.
Land at Nearest Suitable Airport implies a certain urgency due to lack of redundancy. Of course it may be safer to reduce the landing weight depending on the circumstances , so let’s not make absolute statements.
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Old 25th Feb 2019, 18:04
  #25 (permalink)  
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Thanks for all the replies, especially tdracer, and wiggy.
While we all know that the airplane can reject at take off weights so obviously it can land again, this is probably not something we want to do unless in a land immediately situation, Tires melted for sure, probably the brakes finished, and maybe even an evacuation due to a brake fire underneath all the fuel. I have seen some pretty dramatic videos of near V1 reject flight testing.

My own airline had a few cases of airplanes returning heavy after flap issues. The performance charts said it could be done, and it could (and was). The last one required the mechanics to cut the melted brakes off the axles. We were then issued non mandatory "guidance" that suggested dumping to max landing weight (or more if required) any time we were dealing with an aircraft problem. Obviously this requires flying around in circles for half an hour in the manner FlightDetent alluded to. And obviously you wouldn't do this if there was any doubt as to the integrity of the other engine or if something was on fire, but the risk of an apparently healthy ETOPS certified engine failing in a particular 30 minute period should be extremely remote. Our guidance will try and have us avoid dumping unnecessary fuel and land overweight if there is nothing wrong with the airplane and runway length permits.

I guess I can see the logic with this. An overweight landing requires a gentle(ish) touchdown in the touchdown zone to take advantage of all the available runway. An engine out, flap, or flight control issue introduces potential handling complications that could work against the objectives of the overweight landing. Why combine the two if you don't have to?

Anyway, we saw this in a sim scenario and I just wondered what the collective wisdom was. On the sim scenario in question, the matter was resolved by a pop up notam that reduced the useable runway length and required dumping fuel.

Cheers Cropduster.
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Old 25th Feb 2019, 18:12
  #26 (permalink)  
 
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There is a huge difference between holding on a single engine and holding on two good engines.
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Old 25th Feb 2019, 23:09
  #27 (permalink)  
 
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It's a good subject Cropduster, and inevitably generates opposing opinions because there is truth on both sides.

I wonder if you are extending your companies guidance beyond it's original intent, which seems to relate to non-time critical problems (such as flaps)?
The ETOPs thing comes up quite a bit and it is true; engine reliability is such that you could argue that the balance of risk favours increasing the flight time rather than accepting the reduced margin for safety in a high energy landing. However it's not that simple:
I can think of a couple of cases off the top of my head where the "good" engine was discovered to have a problem on landing (eg LOT 787 diversion to JFK recently).
A properly planned overweight landing uses far less energy than the one in spectacular RTO certification videos as you have at least twice the available stopping distance and a thrust reverser. The brake fuses will probably deflate the tires but that is accepted as part of the aircraft design.
Jettisoning fuel may be problematic in environmentally sensitive areas. If you don't want to fly off to a remote designated fuel jettison area, you may have to invoke emergency authority. Which is fine but could you justify that if the performance was adequate to safely land overweight?
Boeing designed the thing to land above MLW in emergencies. FAR regs do not even require it to have a jettison system.

Having said all that, my philosophy is that if circumstances permit I will start fuel jettison as soon as possible and then do an unhurried set up for landing. I'll figure out the maximum acceptable landing weight during this time using a nice fat margin. The resulting landing may or may not be overweight.
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Old 26th Feb 2019, 00:25
  #28 (permalink)  
 
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[COLOR=left=#000000]FAR regs do not even require it to have a jettison system.[/COLOR]
Are you sure about that part? It may not be spelled out in the FARs, but good luck certifying without one if there is a big delta between MTOW and Max Landing.
At EIS, the 767 didn't have a fuel jettison - but Max TO was 330k lbs., and Max Landing was 320k lbs. - so no big deal. But then Boeing started jacking the max TO weight - eventually getting over 400k lbs., but max landing didn't change. The FAA mandated Boeing install a fuel jettison system, and even went so far as to force it be retrofit to a few already delivered aircraft.
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Old 26th Feb 2019, 03:46
  #29 (permalink)  
 
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Pretty sure...

AERO - Overweight Landing? Fuel Jettison? What To Consider

But who knows...in a big organization corporate memory can get pretty foggy.
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Old 26th Feb 2019, 12:03
  #30 (permalink)  
 
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Originally Posted by tdracer View Post
Are you sure about that part? It may not be spelled out in the FARs, but good luck certifying without one if there is a big delta between MTOW and Max Landing.
At EIS, the 767 didn't have a fuel jettison - but Max TO was 330k lbs., and Max Landing was 320k lbs. - so no big deal. But then Boeing started jacking the max TO weight - eventually getting over 400k lbs., but max landing didn't change. The FAA mandated Boeing install a fuel jettison system, and even went so far as to force it be retrofit to a few already delivered aircraft.
The requirement for a fuel jettison system depends on climb performance at MTOW not the MTOW MLW Delta. FAR 25.1001
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Old 26th Feb 2019, 16:07
  #31 (permalink)  
 
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Originally Posted by Cloudtopper View Post


Why?
Back it up ol boy.

What is the the reason the donk failed. What do you do when the second fails - while dumping - while you send your beloved Acars to your ops .

Do you not brief these type of scenarios before take off.
Are you familiar with your AFM.

First of all I’m not your “old boy”.
Second I’m familiar with my AFM thank you.
Third we brief a catastrophic failure and immediate return and not the other 1327 scenarios.

Boeing prohibits auto land when overweight on the type I fly.
That may be an important consideration in the event of further cascading failures.
Your departure airport may not be the best choice to return to for a myriad of reasons.
An uncontained faikure followed by an uncontrollable fire would be a reason for immediate overweight return.
Anything else which may prevent you from continuing to your destination would require additional analysis and decision making which requires time.
The world famous Thompson bird incident caught on tape is a prime example as to why I would decide to dump fuel to land below max landing weight.
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Old 26th Feb 2019, 17:36
  #32 (permalink)  
 
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Cropduster,
A lesson from this debate is not to invent concerns / scenarios or use unfounded ‘certainties’ or ‘guesses’ to justify a course of action.

Based on certification tests, tyres do not ‘melt’, rarely suffer blow outs (antiskid still works), but more likely the protective fusible plugs will deflate them.
Don’t believe all that you see on web videos. Were the tests shown certification successes or otherwise? Many of those RTOs could have been acceptable, which includes allowable deflating tyres and brake fires which must be ‘contained’ without intervention for 5 mins.
Fuel concerns, etc, in abnormal circumstances have been considered in certification, have been flown, and as necessary, demonstrated.
Brakes will be used up to their limit, there may be apparent fire, or brake damage … but that’s inconsequential to the safety decision in planning an overweight landing.

‘A gentle touchdown’; unless your normal landings are greater than 6 ft/sec, then an overweight landing can be flown as a normal landing.
Don’t invent new procedures where none are required.
Don’t create concerns which could distract from the choice of the safest course of action.
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Old 26th Feb 2019, 21:07
  #33 (permalink)  
 
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Or you could fly your A320 over London for nearly thirty minutes,minus its cowls,and then land with smoke coming from one!
Did anyone come up with the reason why that crew stayed airborne for so long?

If you've lost one,and there's asphalt long enough to take you,get it on the ground,and don't wait for SOD or his copilot,MURPHY, to get you by the short and curlies!..Or you could fly round and round in circles,talking to company,dumping fuel,and hope a large bird doesn't go down the other one!

Last edited by Yaw String; 27th Feb 2019 at 21:27.
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Old 27th Feb 2019, 08:35
  #34 (permalink)  
 
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Originally Posted by B2N2 View Post
The world famous Thompson bird incident caught on tape is a prime example as to why I would decide to dump fuel to land below max landing weight.
Well that was a 757 so they didn`t dump fuel - whats your point?
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Old 27th Feb 2019, 12:47
  #35 (permalink)  
 
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Cloudtopper

Originally Posted by [b]dixi188
Overweight landing only when you have no time to dump!
Why cook the brakes and tyres?
please substantiate this reply .

Whilst the aircraft is certified to stop from V1 at Max T.O. weight, the wheels and brakes will almost certainly be cooked and tyres deflated. In an overweight landing with Max Autobrake selected, I think the result would be the similar.
I have only ever done these Max weight excercises in the Sim, but with Carbon brakes on the A300, the brake temps went off the scale, (over 700 degrees C). I don't see the B777 being very different.

Obviously, with the Fuel Dump inop. there is little choice but to land overweight, and with a long runway and lighter braking then the brakes could be saved.

My thoughts,

Dixi188
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Old 28th Feb 2019, 10:35
  #36 (permalink)  

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Dixi188, the MTOW RTOW runs are done with brakes worn down to 25% and will cook them, as well as blow the tyres at the stop - it is a destructive test, agreed until this point. I haven't seen the numbers, so guessing here: the deceleration part eats about 1000 m.

The difference of opinions lies in how much of that actually applies for the overweight landing case in standard configuration. The approach speeds with landing flap tend to be 10% less than at liftoff, which alone provides a dramatic decrease of E(k) in the benefit of the return scenario. The pilots have all of the 3000m-ish runway at their disposal and there is no need to stop by the 1200 meters mark.

Thus our argument that destruction of the wheel assembly due to excessive braking energy does not enter the assessment matrix for an immediate landing at MTOW.
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Old 28th Feb 2019, 15:31
  #37 (permalink)  
 
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Originally Posted by wiggy View Post
Boeing’s thoughts here, (probably based on some of the testing tdracer was involved in):

https://www.boeing.com/commercial/ae...icle_03_1.html
.... and the answer is :

FAR criteria require that landing gear design be based on:

-A sink rate of 10 feet per second at the maximum design landing weight; [...]


which equates to a touch-down vertical speed of 600 fpm !

However, in many AMM Ch 5 , the 'Overweight Landing' inspection is much reduced if the
vertical speed at touch-down is very low (FDR redout helps).
A high-vertical speed touch-down in overweight condition will surely make nasty damages to wing and/or LG
and/or other structure.
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Old 6th Mar 2019, 10:46
  #38 (permalink)  
 
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Originally Posted by B2N2 View Post


First of all I’m not your “old boy”.
Second I’m familiar with my AFM thank you.
Third we brief a catastrophic failure and immediate return and not the other 1327 scenarios.

Boeing prohibits auto land when overweight on the type I fly.
That may be an important consideration in the event of further cascading failures.
Your departure airport may not be the best choice to return to for a myriad of reasons.
An uncontained faikure followed by an uncontrollable fire would be a reason for immediate overweight return.
Anything else which may prevent you from continuing to your destination would require additional analysis and decision making which requires time.
The world famous Thompson bird incident caught on tape is a prime example as to why I would decide to dump fuel to land below max landing weight.

Are you sure you're flying a T7?

Boeing does not prohibit an overweight autoland. They merely state in the AFM (which should be no different to the one you read) it is not recommended.
There is a distinct difference in how you paint the picture.
Cheerio!
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Old 6th Mar 2019, 16:33
  #39 (permalink)  
 
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Let me throw another small hand grenade into the discussion. Imagine that your company policy is not to land overweight unless it would be dangerous not to. Imagine also that when first aquired by your company the aircraft had a certificated weight of say 66 Tonnes.

Since they were not really using that landing weight the company then chose to re-certificate the aircraft to a lower max landing weight in order to save money. Guess what? The lower certificated landing weight now becomes the weight on which you are required to base your decisions.

So to summarise, last week you are not landing overweight, this week you are.
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Old 6th Mar 2019, 17:28
  #40 (permalink)  
 
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Originally Posted by Cloudtopper View Post
Are you sure you're flying a T7?

Boeing does not prohibit an overweight autoland. They merely state in the AFM (which should be no different to the one you read) it is not recommended.
There is a distinct difference in how you paint the picture.
Cheerio!
Ok now you’re arguing about manufacturers recommendations.
Of it’s not recommended it should be avoided except in dire straits.
Which we’re not in this scenario.
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