SIL 3308-10 PG INSERT
Page 2 of 2
The SN3308 has a Fast Slave Mode which turns the card at 25
deg/sec. The heading is redlined during this operation for a
minimum of approximately 7 seconds. Fast slave mode normally
occurs once per flight when systems are powered up. Fast Slave
mode may also occur at any time the Compass Card does not match
North from the fluxgate for more than 25 degrees for more than 2
minutes. This delay is incorporated to ensure that no fast-slaving
operation occurs during turns, when the fluxgate (like the compass)
is not level.
Fast Slaving is an abnormal condition during flight. It can be
caused by a defect or error in either the remote gyro, the remote
fluxgate, an undetected fault in the SN3308, or aircraft wiring, or
from any cause (including all mechanical fluxgate failures) which
would allow the compass card and fluxgate heading to stay
diverged. If it occurs during flight the card will realign to the
fluxgate signal, even if the fluxgate is incorrect.
Fast slaving is automatic. If a fast slave occurs inflight or the
compass digits redline, cross-compare the HSI heading to magnetic
compass (wet compass) heading with wings level. Pilots normally
navigate by flying magnetic track from point to point. Comparing
compass heading to actual track is also a good way to detect a
compass heading error.
Other systems rely on the SN3500’s heading output and could affect
things such as traffic, lightning position, and GPS map displays. If
the autopilot is engaged during fast slave the auto-pilot will follow
the heading bug or the course pointer and should be disengaged. If
there is to be any action taken by the pilot other than disengagement
of the autopilot – especially on an approach – ATC should be
notified immediately of the system malfunction while
simultaneously executing a missed approach and relative heading
direction assistance should be requested.
