Strange Plane Behavior: Explaining Graphs from the Black Box

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Discussion Overview

The discussion revolves around the interpretation of flight data graphs from a plane's black box, specifically focusing on the relationship between ground speed, airspeed, and the plane's descent behavior. Participants explore the implications of the data regarding the plane's motion during a critical phase of flight.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions whether the interpretation of the data showing the plane falling while slowing down is correct.
  • Another participant suggests that the plane may have entered a tail spin, which could explain a dramatic slowdown in speed.
  • A different participant challenges the tail spin hypothesis, requesting yaw port data and emphasizing the importance of distinguishing between groundspeed and airspeed.
  • One participant acknowledges a mistake in plotting groundspeed instead of airspeed, suggesting that the plane was indeed descending rapidly.
  • Another participant posits that the plane was in a mild dive before rolling over and pitching down more steeply, indicating that while ground speed slowed, airspeed might have increased.

Areas of Agreement / Disagreement

Participants express differing interpretations of the data, with no consensus reached on the exact nature of the plane's behavior during the descent. Multiple competing views remain regarding the implications of the plotted data.

Contextual Notes

Participants note the importance of distinguishing between groundspeed and airspeed, and there is an acknowledgment of the need for additional data (e.g., yaw port data) to clarify the situation. Some assumptions about the data interpretation remain unverified.

jumpjack
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Don't know if this is the right place for such a question...

I plotted these graphs based on data taken from the black box of a plane:

http://www.planetmobile.it/jumpjack/immagini/volo93-grafici.GIF

I can't fully understand these data: looks like while the plane was falling down, it was also slowing down. Is this interpreataion correct? How could it be explained?
 
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The plane seems to have entered a tail spin, which would slow down its speed dramatically.
 
How do you get a tail spin from that? I would like to see some yaw port data before jumping there.

You are looking at groundspeed, not airspeed. With a huge roll rate and pitch down it's possible that this thing is falling at a very steep rate which is shown on the altitude plot. Do you have any data on airspeed?
 
Sorry, my mistake, I plotted GROUND speed rather than AIR speed, so I guess it's correct, being the plane going down very fast.

Here you find full FDR data, you want to play with them. ;-)
http://www.crono911.net/doc0/FOIA/UA93tab.zip
 
It just looks to me like the plane was in a mild dive, then rolled over and pitched down more steeply. Ground speed slowed because of the angle of the dive - airspeed probably went up, though not necessarily.
 

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