Sender: <marv@lancaironline.net>
To:  lml@lancaironline.net
Date: Thu, 07 Mar 2013 00:16:59 -0500
Message-ID: <redirect-6099271@logan.com>
Received-SPF: neutral
 receiver=logan.com; client-ip=98.139.44.182; envelope-from=browncc1@verizon.net
From: Charles Brown <browncc1@verizon.net>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: quoted-printable
Subject: Pitch hold glitch / resolution
Mime-Version: 1.0 (Apple Message framework v1085)

Airplane:  Legacy RG / IO-550 / G900 / TruTrak Sorceror

Symptoms: =20
1.  Pitch oscillations about selected 12,000' altitude:  +/-60 feet, +/- =
2.5 deg pitch attitude, +/- 250fpm ROC, period 20 sec.
2.  Not as bad at lower altitudes.
3.  No other issues -- lateral, climb, descent, glideslope tracking =
unaffected.

Debug - (credit Zack at TruTrak)
1.  Confirm proper pitch settings on autopilot.
2.  Disconnect static at autopilot (feed cabin pressure to autopilot =
static input); problem disappeared.

Cure - blow out static system from inside out using 90psi compressed =
air.  Problem solved.

Caveat:  When disconnecting the static at the autopilot, plug the =
connection to the static system (OK, in retrospect:  DUH!!!)  Otherwise, =
you get erroneous airspeed indications (high) which introduce =
unnecessary risk.

Lesson:  The Sorceror suffers ill effects from static system lag that =
doesn't show up on the altimeters, which tracked each other perfectly.  =
The size of the error increases with altitude as the pressure gradient =
(dP/dAlt) decays exponentially with altitude.

Remaining mystery:  What was in the static lines?  Nothing visible blew =
out, not even water.  Maybe this will reappear.

Charley Brown
Legacy RG #299   200 hr