Piper ARCHER III Pilot Operating Handbook page 328

SECTION 9
SUPPLEMENT 20
SECTION 3 - EMERGENCY PROCEDURES (continued)
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 Whiskey Compass.
(>10° after compass deviation applied.)
If heading systems differ by more than 10° (after compass deviation applied):
• Use Whiskey Compass for primary heading reference.
High current loads in the vicinity of the Whiskey
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 Whiskey Compass. These items should be
turned OFF prior to comparing the Whiskey Compass to the
PDF heading.
REPORT: VB-1611
9-126, 18 of 30
CAUTION
REVISED: JANUARY 9, 2006
PA-28-181, ARCHER III
ISSUED: JULY 12, 1995