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757 system question

SLUF4

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I came across the CVR recording of Aero Peru 603 on youtube-pretty disturbing-but the captain and FO kept referencing the Rudder Ratio and Mach Trim during this scenario. What information would they be trying to gather from the fact that the rudder ratio and mach trim weren't engaged; or were those just the only messages that came up on the EICAS? I've not flown anything with a rudder ratio so I'm not exactly sure what that does.
 
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Junkflyer

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Rudder ratio allows large rudder movement at slow speeds and limits it at higher speeds. The light means you may not get full deflection. On the 767 you have a crosswind limit for landing with the light on.
 

SLUF4

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Rudder ratio allows large rudder movement at slow speeds and limits it at higher speeds. The light means you may not get full deflection. On the 767 you have a crosswind limit for landing with the light on.

OK thanks; I guess since the system was so screwed up the rudder ratio failed.
 

NAAPilot

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Like Junkflyer said above. The Rudder Ratio allows for large deflection of the rudder at low speeds, and conversely limits rudder deflection at high speeds. On the 757 the rudder ratio light typically is related to a left hydraulic system problem/failure.
 

Captain X

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Doing?

Wow. God bless 'em. It's really amazing they stayed in the air as long as they did because it sounds like they never got much higher than 1000' AGL. Assuming they never really got to 9700' based on Lima's elevation.

Easy to armchair quarterback so this is really just a synopsis on what I gathered and learned.

They had several clues that their ADCs were giving them invalid information but continously tried to use systems that received information from them (A/T, Vertical MCP modes, etc.).

They also had the GPWS and SPS systems giving them information that could have helped diagnose their true situation. It seemed the Captain became very fixated on the very instruments they knew could be suspect. It seems like the FO had a gut feeling with his references to ATTITUDE and ENGINE instruments.

Lastly, their Radio Altimeter could have provided some information that could have helped.

Never underestimate the value of good systems knowledge, a good preflight inspection, watch out for "tunnel vision," and remember PITCH + POWER = PERFORMANCE.

There but for the Grace of God...:(
 
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bubbers44

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Using their ground speed readout and radio altimiter with attitude and power settings might have got them down but they certainly had enough distractions with all the warnings to make it difficult.
 

Dumb Pilot

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I was in Puerto Plata the night that the Virgen Air 75 crashed, it is by far the worst memory of my career. I remember hearing about Aero Peru a few months later and it just took me right back to that evening, I just could not believe that two 75's would crash the same year for the same reason, a piece of tape.

Que Dios les bendiga
 

BOOZENEWS

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Using their ground speed readout and radio altimiter with attitude and power settings might have got them down but they certainly had enough distractions with all the warnings to make it difficult.


And also dumping the cabin pressure and staying below 10K. This way they could have used the cabin altimiter to help.

Not MM Quarterbacking. This is so sad.
 

wmuflyguy

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Was the controller looking at the wrong plane on the radar screen? He kept saying they were at 9700'.
 

BEECH-SLAPPED

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Was the controller looking at the wrong plane on the radar screen? He kept saying they were at 9700'.

A Mode C transponder uses static pressure to transmit a pressure altitude signal to the ground based equipment. The ground computer then corrects the data for the local altimeter setting and displays the data for the controller. Essentially, the transponder and altimeters were using the same erroneous pressure data.
 

wmuflyguy

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A Mode C transponder uses static pressure to transmit a pressure altitude signal to the ground based equipment. The ground computer then corrects the data for the local altimeter setting and displays the data for the controller. Essentially, the transponder and altimeters were using the same erroneous pressure data.

I didn't think about that...good point.
 

SLUF4

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I think it's good to review these incidents and think about what you would do in a situation like this. Like some others said, you would still have your groundspeed readout and RadAlt and I'm sure the 757 has an EGPWS display derived from GPS position. It seemed like they were under the impression that ATC radar would show their actual altitude and not what was given from the transponder. I feel really bad about this, but hopefully it's a reminder to do a thorough preflight and catch this stuff before it becomes a problem.
 

jmreii

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as a pilot and a mechanic, whenever I take an aircraft out of maintenance that has been signed off to return to line service and before doing any preflight check I make sure the maintenance work was accomplished and complete. you would be surprise on what is forgot, opps pop goes the weasel. thank god for that valuable a&p experience.
 
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