joffie
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757 / 767 Speedbrake Safety?

Thu Apr 13, 2006 9:02 am

After watching the documentary on the American Airlines 757 which crashed into the mountains in Cali after the crew became confused, it was noted that one of the main causes of the crash was the First officer raising the speedbrakes, but forgetting to stow, or put them down.

My understanding is, airbus planes if the thrust is put to maximum, the speedbrake will automatically lower to prevent drag. On the 757 / 767 and possibly other boeing planes how come this does not happen? Wouldn't it be alot safer if the speedbrakes would lower if max thrust was applied?

I know there are hundreds of safe flights each day, and this is an extremly rare occurance.

thanks
 
2H4
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RE: 757 / 767 Speedbrake Safety?

Thu Apr 13, 2006 9:31 am




Quoting Joffie (Thread starter):
Wouldn't it be alot safer if the speedbrakes would lower if max thrust was applied?

Haven't 757s and subsequent Boeings been modified to do just that?




2H4


Intentionally Left Blank
 
dc10hound
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RE: 757 / 767 Speedbrake Safety?

Thu Apr 13, 2006 12:41 pm

Haven't 757s and subsequent Boeings been modified to do just that?

Only if the aircraft is on the ground. Forty percent of travel from the idle stops will cause the ground spoilers to reteract. It's part of the function of GA.

All AAL B757s came from the factory that way.
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onetogo
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RE: 757 / 767 Speedbrake Safety?

Thu Apr 13, 2006 1:42 pm

Quoting Joffie (Thread starter):
it was noted that one of the main causes of the crash was the First officer raising the speedbrakes, but forgetting to stow, or put them down.

This is a rather bold statement, especially considering the NTSB concluded that the plane would have impacted terrain regardless of whether the speedbrakes were extended or stowed. Recommend you read the full narrative report sir.
 
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HAWK21M
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RE: 757 / 767 Speedbrake Safety?

Thu Apr 13, 2006 6:14 pm

LINK
regds
MEL
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schooner
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RE: 757 / 767 Speedbrake Safety?

Thu Apr 13, 2006 7:29 pm

SOP in my airline is to keep a hand on the speedbrakes whenever they are deployed in flight, the thinking being you are less likely to inadvertantly leave them up if your hand is resting on them!

Cheers.
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YYZYYT
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RE: 757 / 767 Speedbrake Safety?

Fri Apr 14, 2006 1:27 am

Quoting Onetogo (Reply 3):
This is a rather bold statement, especially considering the NTSB concluded that the plane would have impacted terrain regardless of whether the speedbrakes were extended or stowed. Recommend you read the full narrative report sir.

hmm. I thought I remembered otherwise, so I re-read a portion of the NTSB report:

see bottom of p 50:

"Results of an initial study of the performance of AA965 following the GPWS warning indicates that if the flightcrew had retracted the speedbrakes second after initiating the escape maneuver, the airplane could have been climbing through a position that was 150 feet above the initial impact point. Therefore, because the airplane would have continued to climb and had the potential to increase its rate of climb, it may well have cleared the trees at the top of the ridge. The study also showed that if the speedbrakes had been retracted upon initiation of the escape maneuver and if the pitch attitude had been varied to perfectly maintain the stickshaker activation angle [35] the airplane could have been climbing through a position that was 300 feet above the initial impact point."

Though, Onetogo is not entirely wrong - the failure to retract the speedbrake was not listed as a cause at all, but rahter only as one of the contributing factors: see section 3.3, this is shown as a contributing factor:

"2. The flightcrew's execution of the GPWS escape maneuver while the speedbrakes remained deployed."

Interesting analysis of the issue, needless to say. Here is a link to the report:


http://www.rvs.uni-bielefeld.de/publ...s/DOCS/ComAndRep/Cali/calirep.html

[Edited 2006-04-13 18:29:01]
 
YYZYYT
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RE: 757 / 767 Speedbrake Safety?

Fri Apr 14, 2006 1:29 am

Quoting Schooner (Reply 5):
SOP in my airline is to keep a hand on the speedbrakes whenever they are deployed in flight, the thinking being you are less likely to inadvertantly leave them up if your hand is resting on them!

report notes as well that Boeing recommends exactly this, but that AA did not include this in its own pilot manuals...
 
DH106
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RE: 757 / 767 Speedbrake Safety?

Fri Apr 14, 2006 1:42 am

Quoting YYZYYT (Reply 6):
Though, Onetogo is not entirely wrong

Think I disagree - Onetogo seems to say the report implies impact was inevitable regardless of speedbrake position. The report says "it may well have cleared the trees at the top of the ridge" - although the report doesn't commit itself positivley, and the gist is that timely speedbrake retraction and rapid optimum escape maneuver was required, the report certainly doesn't imply impact was ineviable.
...I watched c-beams glitter in the dark near the Tanhauser Gate....
 
YYZYYT
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RE: 757 / 767 Speedbrake Safety?

Fri Apr 14, 2006 2:00 am

Quoting DH106 (Reply 8):
Think I disagree

I know that - I was referring to Onetogo's challenge to this characterization...

Quoting Joffie (Thread starter):
one of the main causes of the crash was the First officer raising the speedbrakes, but forgetting to stow, or put them down

My point was simply that the truth (as usual) lies somewhere between the two...

And btw, I'm not taking a run at Joffie either... no matter how good these shows are they have to edit the content of hte NTSB report to make it interesting for the average viewer, and to fit the episode into 50 minutes...
 
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Starlionblue
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RE: 757 / 767 Speedbrake Safety?

Fri Apr 14, 2006 5:56 am

Quoting Joffie (Thread starter):
My understanding is, airbus planes if the thrust is put to maximum, the speedbrake will automatically lower to prevent drag. On the 757 / 767 and possibly other boeing planes how come this does not happen? Wouldn't it be alot safer if the speedbrakes would lower if max thrust was applied?

For every person who sees this as an extra safety feature, you will find another person who thinks it is removing "authority" from the pilot.

In the end, if you don't follow procedure, you're doing something wrong and potentially dangerous, regardless of whether there is an extra safety net.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
joffie
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RE: 757 / 767 Speedbrake Safety?

Sat Apr 29, 2006 4:20 pm

Some very information there.

I will sure check the official accident report shortly.

I have also read it is policy to keep your hand on the speedbrake lever when you are using them to slow down in some airlines.

If this is an AA policy, the policy was not followed.

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