The reader is advised to not waste their time with this web page, as it documents a "false start."  As the note at the end explains, the accelerometer feature that appears to be the "light to moderate" CAT event reported by the pilot turns out to be produced by a calibration "porpoise" pitch maneuver performed for the purpose of calibrating the MMS instrument.  I leave the web page here as an illustration of the need to remain ever-vigilant about data that arouses our intuitive suspicion, as this data did for me.  It took several hours of curious follow-up analysis to uncover the real explanation for the putative CAT encounter.


Overview of Flight ER950515

The flight of May 15, 1995 was based at Moffett Field, Mountain View, CA.

Figure 1.  Flight track for ER950515, showing the north/south flight segments.  Time ticks and "kilosecond" labels are shown at 1 ks intervals.

This was a "stack flight" consisting of back-and-forth flight legs at different altitudes.

Figure 2.  Altitude versus latitude, with 1-kilosecond tic marks.  The accelerometer record shows a CAT encounter, indicated by an oval symbol, at 19.65 km, at latitude 39.96 deg.

The pilot reported "light to moderate CAT south of 39 degrees [latitude]," so it is unclear if the pilot was really referring to the "event" at 39.9 degrees.  He also refers to "light CAT at FL 610" which corresponds to the highest altitude flight leg.  If the event at 39.9 degrees is "light" then it is not a suitable candidate for this study.

Lapse Rate

The following figure shows the MTP-measured lapse rate, dT/dZp, for all flight legs.

Figure 3Lapse rate, dT/dZp, and accelerometer peak-to-peak "activity."  The CAT encounter at 78.85 ks appears to be strong, but this accelerometer record has not been calibrated so it might in fact be the "light" event reported by the pilot.

The acceleromter record has not been calibrated, so the 1.00 g-unit excursion is quite likely wrong (I used a calibration from 1994, and several changes were made before the mission from which this data is taken).  After 80 ks, the ER-2 begins its descent, and experiences two more more CAT encounters that appear to be more severe than the one recorded at 79.9 ks.  It is these events, during descent (and south of 38 degrees), that may correspond to the pilot's "light to moderate" report.


Due to the ambiguity of identifying which accelerometer event is "light to moderate" CAT I will not pursue this flight further on behalf of the present task.


Note August 25, 2000.  I just determined that the putative CAT encounter at 78.9 ks was produced by a rare "porpoise" calibration maneuver requested by the MMS team for the purpose of calibrating their instrument.  This situation almost fooled me, and it points up the need to carefully follow-up on data that seems suspicious.  What most caught my suspicion here was the pitch excursions that accompanied the putative CAT encounter.  Although pitch excursions do actually accompany CAT, these seemed too large, and when I expanded the plot scale while checking the accelerometer calibration, I noticed that they had a regular pattern.  I then checked the pilot log carefully, and his instructions for that flight were to perform a porpoise maneuver for MMS after completing the MMS box calibration maneuver, and the box maneuver was clearly performed just prior to the false CAT encounter.  Since the "light to moderate" CAT that was encountered did not occur during level flight, apparently, this flight is not useful for the present analysis objectives!  I will leave this web page linked to the main one as an illustration of the need for all investigators, and readers of investigations, to maintain a healthy skepticism of data that doesn't quite seem "right."  Intuition has its place, as it can alert us to false assumptions, and "bad data."

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This site opened:  August 16, 2000.  Last Update: August 25, 2000