Piper ARCHER III Pilot Operating Handbook page 375

PA-28-181, ARCHER III
Loss of Heading Accuracy
Indication:
• Difficulty maintaining course while using VOR or GPS.
• Excessive difference between heading and track required maintaining a
VOR or GPS course.
• ATC indicates the aircraft is on a wrong heading.
• Excessive deviation between PFD heading and magnetic compass.
(>10° after compass deviation applied.)
If heading systems differ by more than 10° (after compass deviation applied):
• Use magnetic compass for primary heading reference.
High current loads in the vicinity of the magnetic
compass can influence its accuracy. Depending on the
flight conditions, the pilot must reduce these loads as much
as possible to insure accuracy. Tests have shown that air
conditioner and pitot heat contribute to significant heading
errors of the magnetic compass. These items should be
turned OFF prior to comparing the magnetic compass to the
PDF heading.
ISSUED: JULY 12, 1995
REVISED: FEBRUARY 14, 2006
CAUTION
SECTION 9
SUPPLEMENT 23
REPORT: VB-1611
21 of 36, 9-173