Way back when.......... I've pulled contrails with my Cessna T-210 (circa 1974) over Colorado & Kansas in the winter. My Bonanza A36TC would do the same. I don't remember what altitude, but I do remember it was lower than FL250 (maximum "certified" ceiling on both aircraft.) For what's worth, the Bonanza was more "fun" to fly......... Dennis Murphy ----- Original Message ----- From: "W Wilson" <wlw-jr@att.net> To: <AIRLINE@LISTSERV.CUNY.EDU> Sent: Saturday, December 29, 2001 10:05 PM Subject: Re: Contrails > Richard, > Here is a message I left about a month ago on the ComAirScan messge > board...with a few changes. > > Depending on the temperature and humidity, contrails will form starting at > around > FL310 to FL350 (definitely not carved in stone.) . In summer, they may not > form at all. In the northern part > of the US, contrails on a cooler day, may be around FL280 or lower, but > while it can > be cold enough for a contrail, there may not be enough moisture in the air. > Also, except for military aircraft that operate with fuel additives to > prevent contrails, a Learjet can leave a contrail as a 747. Also in the > Arctic, you may have seen photos of Twin Otters and > C-130s leaving trails from start-up, to taxi, thru takeoff. Contrails form > from the hot exhaust rapidly expanding as it hits the colder air...remember > physics... > as air expands, it cools...if it cools to the dewpoint it > condenses...thus a trail of moisture is formed. (in this case, due to the > extremely cold temps...the vapor sublimates directly into ice crystals) > > To answer your Qs. Yes...there can be a narrow band of altitude where > contrails will form...depending on temperature and dewpoint. > > Walter > DCA > > ----- Original Message ----- > From: "Richard A Whitenight" <rum.runner@juno.com> > To: <AIRLINE@LISTSERV.CUNY.EDU> > Sent: Saturday, December 29, 2001 20:58 > Subject: Contrails > > > > Anyone who watches the skies sees the contrails emitting from a jet which > > is obviously in rather cold air <grin>. Why is it that normally only see > > contrails in a narrow band of cold air? Is there a high and low altitude > > where contrails don't form, or is it strictly dependent on the > > temperature of and/or moisture in the air. > > >