Re: Overheard on channel 9 ...

Date:         23 Apr 97 02:58:15 
From: (Thomas O'Toole)
Organization: Av8r Images
References:   1
Followups:    1
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In article <airliners.1997.926@ohare.Chicago.COM>,
>Recently, on a United flight, I was listening to channel 9 (cockpit
>communications).  An airliner of unknown type was cleared to FL 410.  It
>then requested that it be sent no higher that 390.  The controller asked
>why: "don't you have the performance for 410?"  "Yes," came the reply,
>"but not in the light chop that is reported there."
>Could someone explain what was going on here?  Is FL 410 so close to the
>service ceiling that a little chop (and presumably some gusts from the
>rear) are problematic?

At those altitudes the margin between lowspeed buffet and highspeed buffet is
rather low offten a spread of less than 100 Kts.  It could have been that at
their weight their Va(turbulent air penetration) speed was close enough  to
the low speed buffet  that the captain was wary.


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