>>>  Umm, yeah.  Names and other verifiable details conveniently
>>> omitted (even to the type of "navigation gear" that was
>>> affected).  Pilots have several

>> This description sounds somewhat similar to the situation described
>> earlier.  This came from the ASRS Database Report Sets Index

> <big snip including summary of incident>

> I don't understand why the directional gyros are affected and not
> the nav gear!!!!?????? AFAIK, the directional gyros are inertial
> (by definition) and might be slaved to magnetic compass to make
> sure they roughly agree, however, I don't see any way they could
> be affected by RFI. Especially considering that the radio nav
> gear was functioning at least two of the cases.

All gyros precess.  The attitude indicator gyro is corrected
by gravity and ingenious mechanics since most aircraft spend
most of the time in level flight.

In light aircraft, directional gyros are manually corrected
to the magnetic compass using a small knob on the face of the
instrument.  It's needed every 5 to 20 minutes.

In large transport category aircraft, this is automatic.  I
believe that the magnetic sensor is a fluxgate and is commonly
mounted on a wingtip.  It needs to be away from large ferrous
objects like the landing gear.  The connection, obviously, is
a wire between the two.  How sensitive this is to any EMI/RFI...


From a pilot's point of view, I don't understand one thing.
Transport category aircraft are almost always on IFR flight
plans.  They are flying airways defined by VOR radials (the
"nav gear" in 108-118 MHz).

Your heading, as read from the directional gyro & magnetic
compass, should roughly agree.  But if you drift off the
airway, you turn back toward it.  This is quite common when
correcting for wind (cross wind pushing you off track).

Now if interference displaced the directional gyro _and_
the magnetic compass (possible if on same sensor), then they
would not agree with the VOR/airway data.  Your DG heading
would be _way_ off and should raise an obvious red flag to
the pilot.  But you'd be able to track the airway just fine.

                                                Lee Jones