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Runway excursion by DL MD-80

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Runway excursion by DL MD-80

Old 7th Apr 2015, 18:35
  #221 (permalink)  
 
Join Date: Feb 2015
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zeffy, I don't have my MEL list handy. Since you probably do, why not look it up?

Can you dispatch an MD80 with one thrust reverser inop?

Does the MEL indicate that BOTH reversers must be made inop by wiring both reverse levers closed or allow one reverser to be used and if so what limits?


Dear Aluminum Shuffler. Would you classify the Sioux City crash as cowboying, or improvising in an odd situation? They used differential/assymetric thrust didn't they?

There is so much misunderstanding of the art of flying, which is largely done with the mind. Bubbers indicated thinking of the reversers as the reins of a horse is a way of THINKING. It would be very nice if people started THINKING and actually reading things.

Simple question: if you were in trouble and could not control the plane with conventional methods, would you try differential/assymetric thrust, or just give up?
skyhighfallguy is offline  
Old 8th Apr 2015, 00:25
  #222 (permalink)  
 
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I've never seen it written or said that you can't use asymmetric reverse thrust. The only guidance I have seen is that it may "make directional control difficult", but if you're attempting to use it to re-gain directional control, that could be a bad idea (thrust changes don't happen immediately), unless loss of control in attempting to stop is preferable to not trying...

The reason reverse thrusters get locked out is to prevent inadvertent deployment in flight.
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Old 8th Apr 2015, 00:43
  #223 (permalink)  
 
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When I flew the MD80 we could dispatch with one reverser inop per our MEL.


The restriction was 'idle reverse only'


There is no 'experience waiver' for manufacturers operation
recommendations !


If you disregard them you have become a test pilot and opened yourself up to unlimited liability.
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Old 8th Apr 2015, 01:19
  #224 (permalink)  
 
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stilton and others

thanks for the MEL confirmation you can go with one TR inop.

And that you can use idle reverse.

IDLE reverse on one side and forward thrust on the other side is assymetric.


hmmmmmmm
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Old 8th Apr 2015, 03:12
  #225 (permalink)  
 
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You must be 'Skyhigh' if you think that idle reverse on one side has any significant asymmetric affect.


You have no idea what you're talking about.
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Old 8th Apr 2015, 03:12
  #226 (permalink)  
 
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Landed a 757 on a short runway in the mountains in Central America one day and only the right reverser deployed so used it normally with no problem staying on centerline with a bit of opposite rudder.

Of course if it was icy the plane would have turned in the direction of the reversing engine so I would have had to reduce or cancel reverse because the rudder couldn't compensate for the reverse at lower speeds.

Amazing how that works.
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Old 8th Apr 2015, 03:33
  #227 (permalink)  
 
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stilton

forward idle, reverse idle= assymetric.

ask an engineer (not a mechanic)

gotcha stilton. gee, stilton, that's a smelly cheese right?

And I don't know what I'm talking about? Well, then how did I know what the answer was for the MEL'ing of a thrust reverser .
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Old 8th Apr 2015, 06:39
  #228 (permalink)  
 
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Originally Posted by skyhigh
forward idle, reverse idle= assymetric.
Knock it off, stilton didn't say it was not asymmetric, he talked about the "significant asymmetric effect". Big difference.
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Old 8th Apr 2015, 08:12
  #229 (permalink)  
 
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Sky
What several posters are pointing out is that there is specific authorised information about the use of reverse, the idea that one should use asymmetric reverse to regain directional control is contrary to that.
The mel item allows one reverse inop. It does not mean that you would play around trying to stear using asymmetric power! Further the manuals clearly state if directional control is lost to cancel reverse, this will apply whether one TR is inop or not.
You qoute Sioux City as part of your defence.....WTF? That is clearly not the same. and has no relevance to this incident.
You accuse others of not reading correctly, perhaps you should take a close look at your own behaviour.
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Old 8th Apr 2015, 09:53
  #230 (permalink)  
 
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Fine. let's do it your way.

go out of control and get out of reverse. fine

then why didn't these guys do that? why didn't they have the nosewheel on the ground prior to selecting reverse?

why was the assymetric reverse thrust successful at pulling the plane to the excursion side?
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Old 8th Apr 2015, 10:17
  #231 (permalink)  
 
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What about reverser use during an RTO just below V1. How about the same on a slippery runway?

Is it idle reverse only?
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Old 8th Apr 2015, 18:54
  #232 (permalink)  
 
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jammed stab

they won't answer. they cannot fathom the ideas expressed here. Your question is quite valid.

Reverse can be used in any way when you need it and CAN MAINTAIN CONTROL>

I have never said use assymetric reverse and LOSE CONTROL.

And if you do lose one engine before V1 or at V1 and elect to reject the takeoff, you deploy both reversers, as they will create drag at the least and can attenuate forward idle. But if you can MAINTAIN control you can use remaining reverse.
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Old 8th Apr 2015, 21:42
  #233 (permalink)  
 
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This is probably a dumb SLF question, but wouldn't the effect of asymmetric reverse thrust be limited with tail mounted engines?
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Old 8th Apr 2015, 22:12
  #234 (permalink)  
 
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hi chu chu

it is a reasonable question. many factors come into play. One is that the tail mounted engines , when reversers are deployed, interfere with airflow over the rudder, reducing the aerodynamic effectiveness.

But you are right the lever arm is much shorter on a tail mounted engine so it would be less assymetric than a wing mounted engine.

HOWEVER most wing mounted engine planes now a days use higher bypass engines and their thrust reversers are a different type than on the MD80. They are inherently less effective.

So it is an apples or oranges comparison.

I have flown 9 and 737 with the same engines and same types of reversers and that is a better comparison. Prefer the tailmounted engines.

the main topic on this forum seems to be the blanket statement about using assymetric reverse thrust for directional control. IT is tricky to do and you either have the touch or don't and the blanket statement covers those who don't.

IT IS VERY IMPORTANT TO PUSH FORWARD ON THE CONTROL WHEEL to insure the nosewheel is in firm contact of the runway as it aids in directional control.

IT IS Important to note that the maximum EPR (engine pressure ratio) was exceeded early on in the landing.
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Old 9th Apr 2015, 04:41
  #235 (permalink)  
 
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Returning to Brussels in a 1-11 in the 1970s after one of the engines went bang just as the nose was lifting, we did an interesting zig-zag landing (interesting for passengers such as I). First the good engine revved up (reverse thrust) and we veered off quite sharply to one side (towards one line of fire engines). Then the good engine revved down and the brakes came on (presumably the brakes on the wheels on the other side only) and we veered off towards the line of fire engines on the other side. We turned like this about six times, repeating the same procedure. Question: does every pilot practise such manoeuvres these days?
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Old 9th Apr 2015, 05:30
  #236 (permalink)  
 
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skyhighfallguy:
IT is tricky to do and you either have the touch or don't and the blanket statement covers those who don't.
So how do you find out if you do or don't? I'd rather not fly with those who are hell bent on testing out their capabilities.
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Old 9th Apr 2015, 13:07
  #237 (permalink)  
 
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ancient mariner

I guess you would really have to fly planes with thrust reverseres to understand my comment.

I've seen pilots pull on reverse and get it wrong. Engines never come up at the same rate, sometimes the rigging is wrong on the reverse levers. And you develop a touch. A touch for the type and for the particular plane.

The flight in question had assymetric reverse and it seems to have pulled the plane to one side. Had they altered that they might have been able to pull the plane back towards centerline.

Directional control with aerodynamic or nosewheel steering is preferred, but if you are going off the side, wouldn't you try assymetric thrust?
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Old 9th Apr 2015, 13:12
  #238 (permalink)  
 
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but if you are going off the side, wouldn't you try assymetric thrust?
Me? Never, as I'm not a pilot.
Just wondering how you would train on using asymmetric thrust for directional control on the ground. Sim?
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Old 9th Apr 2015, 13:20
  #239 (permalink)  
 
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re reading the handout, it says MAINTAIN directional control, not re establish directional control when you are headed off the side of the runway.

ancient mariner, in the real world, reversers do not deploy at the same instant, and engines do not spool up at the same rate, therefore you gain real world experience with assymetric thrust while attempting to establish equal thrust.

bubbers has spoken of the "REINS" technique and he is correct, you find one engine putting out more thrust than another engine. You find the plane pointing to one side or the other, you can look down and make your adjustments on the EPR gauge or you can "take the reins" and establish an equal amount of thrust

I guess you will have to go out and learn to fly ancient mariner to fully understand.

IF the plane's nose is going left, you pull back a little more on the right reverse lever, IF YOU can't maintain aerodynamic or nosewheel control. IF the engine EPR gauges show you are producing more thrust on the left engine (while reverser is deployed) you push forward on the left reverser lever and pull back a little on the right (increasing reverse) to balance them


YOU GAIN experience with assymetric thrust by trying to avoid its use, but you have this experience if you ever need to use it.
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Old 9th Apr 2015, 13:51
  #240 (permalink)  
 
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Most landings runway length is not critical so brakes are not used until around 80 knots to save on brake wear on my airline. I used the same technique prior to the airlines also.

From reverser deployment to 80 knots small rudder inputs are used to maintain centerline tracking. Crosswinds and assymetrical thrust application would be the main reasons for correction to remain on centerline. This is the time to see the results of a bit of assymetrical thrust to maintain centerline using rudders if necessary to maintain centerline tracking. It will soon become easy and instrinctive so one day when things go south you have that extra tool to bail you out of a situation.

You haven't broken any rules because no pilot can keep perfectly balanced reverse power anyway when most of your attention is directed out the front window.

Obviously it wasn't in this crash causing it from the start.
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