From: Tony Williams
Subject: Re: (Avionics) How can this circuit produce an "inductive surge"?
Date: Thu, 26 Sep 2002 16:34:04 +0100
NNTP-Posting-Date: Thu, 26 Sep 2002 15:36:20 +0000 (UTC)
User-Agent: Pluto/1.14i (RISC-OS/3.60)
In article ,
> The normal procedure in light airfraft startup/shutdown is to have all
> possible avionics disconnected when the engine is being started or
> Moreover, one is normally advised to have the alternator field circuit
> broken at these times (there is a switch for this purpose).
> There are many stories going around of somebody's entire avionics kit
> getting blown up if this procedure is not followed.
Weight and cost are important in an aircraft, so
if something is there then there is a good reason
for it to be there. The reason being safety of
course. It is possible that in the past there
have been a sufficient number of accidents (which
were found to originate from an uncontrolled
generator), for this procedure to become standard
Powering up/down, running up/down is a time of
uncertainty for electronic equipment. No matter
how small, there is a chance that the field coil
could be energised. The failsafe thing to do
is to have the output isolated during such periods
and to have the field coil, not only unenergised,
but also physically shorted.