Return-Path: Sender: (Marvin Kaye) To: lml@lancaironline.net Date: Tue, 16 Dec 2003 22:07:24 -0500 Message-ID: X-Original-Return-Path: Received: from imo-r08.mx.aol.com ([152.163.225.104] verified) by logan.com (CommuniGate Pro SMTP 4.1.8) with ESMTP id 2893774 for lml@lancaironline.net; Tue, 16 Dec 2003 19:46:49 -0500 Received: from Sky2high@aol.com by imo-r08.mx.aol.com (mail_out_v36_r4.8.) id q.1eb.15888646 (1320) for ; Tue, 16 Dec 2003 19:46:43 -0500 (EST) From: Sky2high@aol.com X-Original-Message-ID: <1eb.15888646.2d110172@aol.com> X-Original-Date: Tue, 16 Dec 2003 19:46:42 EST Subject: Further to the Further to the S-Tec AP Anomaly X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1071622002" X-Mailer: Thailand for Windows sub 300 -------------------------------1071622002 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en My AP computer is being carried in the belly of a freighter, on its way to=20 S-Tec. After a long conversation today with an S-Tec tech, the following wa= s a=20 preliminary analysis (autopsy to be performed later): Attention was focused on IC #7 on the =E2=80=9CPitch=E2=80=9D board which pe= rforms a=20 comparator function for the Turn Coordinator gyro tach sensor with one of th= e legs=20 holding 10 VDC. It may have failed in a way that compromised the tach line=20= and=20 introduced an erroneous 10 VDC to it. Further conversation was about how the failure might occur: A post 9-11 flight in fairly bad weather that included peculiar and=20 particularly potent p-static (very strong squeals and pops in my Bose headse= t, several=20 GPSS signal retention errors requiring recycling the AP and ATC communicatio= n=20 difficulties) may have resulted in causing the trim fuse (F1) to fail and th= e=20 loss of the AP. This was repaired at a stop in Casper, WY. The same "spike= " =20 that whacked the fuse may have failed the IC. I may have been flying for 2=20 years with a serious accident waiting to happen. Luckily, I don't have to b= e=20 anywhere at any specific time. I just have to be somewhere, as determined by= =20 GPS, most of the time - not counting out-of-body experiences. ------------ In any event, this is a dangerous condition in that IFR operation with a=20 failing TC gyro could lead to an unrecoverable unusual attitude =E2=80=93 ju= st something=20 that the AP was installed to protect this pilot from in the event of a vacuu= m=20 failure. There is no check that the gyro data is valid at all, or even=20 present. If the airplane slowly rolls over and enters an inverted dive whil= e in=20 altitude hold - thus "pulling" even more up elevator, the inverted series of= =20 descending loops will eventually wake up the pilot, shortly before impact. =20 The test I recommended pilots to make is not a certainty that things are=20 working well =E2=80=93 just that if they experience the ready light with the= TC breaker=20 off, there is a serious A/P problem they must correct ASAP, and certainly be= fore=20 entering IMC. Scott Krueger Sky2high@aol.com II-P N92EX IO320 Aurora, IL (KARR) "...as we know, there are known knowns; there are things we know we know. We= =20 also know there are known unknowns; that is to say we know there are some=20 things we do not know. But there are also unknown unknowns - the ones we don= 't=20 know we don't know." D. Rumsfeld -------------------------------1071622002 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en
My AP computer is being carried in the belly of a freighter, on its way= to=20 S-Tec.  After a long conversation today with an S-Tec tech, the followi= ng=20 was a preliminary analysis (autopsy to be performed later):
 
Attention=20 was focused on IC #7 on the =E2=80=9CPitch=E2=80=9D board which perform= s a comparator=20 function for the Turn Coordinator gyro tach sensor with one of the legs hold= ing=20 10 VDC.  It may have failed in= a way=20 that compromised the tach line and introduced an erroneous 10 VDC to=20 it.
 
Further=20 conversation was about how the failure might occur:
 

A post 9-11 flight in fai= rly bad=20 weather that included peculiar and particularly potent p-static (very strong= =20 squeals and pops in my Bose headset, several GPSS signal retention errors=20 requiring recycling the AP and ATC communication difficulties) may have resu= lted=20 in causing the trim fuse (F1) to fail and the loss of the AP.  This was repaired at a stop in=20 Casper, WY.  The same "spike"  that wh= acked=20 the fuse may have failed the IC.  I may have been flying for 2 years wi= th a=20 serious accident waiting to happen.  Luckily, I don't have to be anywhe= re=20 at any specific time. I just have to be somewhere, as determined by GPS, mos= t of=20 the time - not counting out-of-body experiences.

 

------------

 

In any event, this is a=20 dangerous condition in that IFR operation with a failing TC gyro could=20= lead=20 to an unrecoverable unusual attitude =E2=80=93 just something that the AP wa= s installed=20 to protect this pilot from in the event of a vacuum failure.  There is no check that the gyro da= ta is=20 valid at all, or even present.  If the airplane slowly rolls over and=20 enters an inverted dive while in altitude hold - thus "pulling" even mo= re=20 up elevator, the inverted series of descending loops will eventually wake up= the=20 pilot, shortly before impact.

 

The test I=20 recommended pilots to make is not a certainty that things are work= ing=20 well =E2=80=93 just that if they experience the ready light with the TC brea= ker off,=20 there is a serious A/P problem they must correct ASAP, and certainly be= fore=20 entering IMC.

 

Scott=20 Krueger
Sky2high@aol.com
II-P N92EX IO320 Aurora, IL (KARR)

"..= .as=20 we know, there are known knowns; there are things we know we know. We also k= now=20 there are known unknowns; that is to say we know there are some things we do= not=20 know. But there are also unknown unknowns - the ones we don't know we don't=20 know." D. Rumsfeld
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