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PAI-700-28V – Precision Aviation Vertical Card Magnetic Compass (28V) 🧭
Available now on the Airparts.aero Marketplace.
Overview
The Precision Aviation PAI-700-28V is a state-of-the-art Vertical Card Magnetic Compass designed to replace traditional, fluid-damped "whiskey compasses" in aircraft with a 28 Volt electrical system. This instrument is fully TSO-C7c Type 1 certified, satisfying the FAA regulatory requirement for every aircraft to have a magnetic compass. The PAI-700-28V provides an intuitive, easy-to-read directional display that closely mimics a directional gyro (DG), thereby reducing pilot workload and minimizing reading errors, especially during turning or maneuvering flight.
Unlike older designs, the PAI-700 is a dry compass, eliminating issues associated with fluid leakage, bubble formation, and chemical odor. Its operational reliability is paramount, as the magnetic compass serves as the ultimate, non-powered backup for the aircraft's primary heading reference systems (HRUs or AHRS). The $-28V$ suffix specifically indicates the voltage required for the integrated instrument lighting system, while the magnetic sensing element itself requires no electrical power to operate.
Key Features
Vertical Card Presentation: Displays the full 360 degree rotating dial vertically, allowing the pilot to read the magnetic heading directly at the 12 o'clock position, relative to a fixed miniature airplane (lubber line).
Dry Magnetic Design: Contains no fluid, eliminating common issues such as fluid leaks, bubble formation, and pendulous errors associated with liquid-filled compasses.
Eddy Current Damping: Utilizes an integrated eddy current mechanism to dampen oscillations and magnet movement, resulting in reduced overswing and inherent stability compared to fluid damping.
Reduced Magnetic Errors: The captive vertical mounting of the sensing magnet significantly reduces the effects of pendulosity and common errors like "acceleration/deceleration error" and "northerly turning error."
TSO Certified: Fully manufactured under the authorization of the FAA, compliant with TSO-C7c Type 1 Directional Instrument, Non-Stabilized, ensuring certified performance and reliability.
Integrated 28 Volt Lighting: Includes an internal light bar assembly designed to operate on the aircraft's standard 28 VDC electrical system for night and low-light operation.
Technical Specifications
Part Number: PAI-700-28V
Component Type: Vertical Card Magnetic Compass
OEM Manufacturer: Precision Aviation, Inc.
Lighting Voltage: 28 VDC (Also available in 14 VDC and 5 VDC models).
Mechanism: Dry Magnetic with Eddy Current Damping.
Mounting Standard: Designed to fit into a standard $\text{2 1/4}$ inch (57 mm) instrument panel cutout, typically utilizing a custom glare shield or post mounting bracket (sold separately).
Dimensions (Approximate): 2.875 inches (H) x 2.375 inches (W) x 2.125 inches (D).
Weight (Approximate): 0.6 lb.
Certification Status: Fully TSO-C7c Type 1 Approved.
Compensator: Equipped with a poly-plane compensator providing a deviation correction range of approximately $\pm 20$ degrees on the cardinal headings.
Aircraft Compatibility
Primary Usage: Suitable for most General Aviation (GA) aircraft, helicopters, and sailplanes as a certified primary magnetic compass.
Specific Applications: Commonly installed in aircraft requiring a more intuitive heading display, often replacing the older Airpath or similar liquid compasses. Custom mounting brackets are available for popular models including Cessna 150-210 series, Piper models (Cherokee/Arrow/Lance), Beechcraft Bonanza/Baron, and Robinson helicopters.
Verification Note: The installation must adhere to the aircraft's Type Certificate Data Sheet (TCDS) and the PAI-700 Installation Manual regarding mounting location and minimum magnetic interference clearances.
Applications Section
The PAI-700-28V serves as the fundamental Magnetic Heading Reference for the aircraft:
Primary Backup: Provides a completely autonomous, non-electrically dependent heading reference required by regulations, critical in the event of total electrical failure or primary avionics (AHRS/GPS) failure.
Compass Compensation: Contains internal compensator magnets for the removal of deviation—errors caused by the aircraft's inherent magnetic fields (ferrous metal, electrical currents).
Instrument Panel Integration: Fits the standard $\text{2 1/4}$ inch instrument panel hole for simplified installation, unlike larger, post-mounted traditional compasses.
Why Choose the PAI-700-28V Vertical Card Compass?
The Precision Aviation PAI-700-28V offers a tangible safety and ergonomic upgrade over traditional compasses. Its dry, vertical-card design eliminates the "backward" reading inherent in older compasses and greatly reduces pilot fatigue and confusion by aligning the display with the pilot's natural perception of turns. Crucially, the use of eddy current damping provides superior stability by minimizing the compass's overswing after turbulence or a maneuver. This TSO-certified instrument ensures the highest degree of reliability, optical clarity, and adherence to the required magnetic alignment forces, which are critical for accurate long-distance navigation and regulatory compliance.
The stability of the PAI-700 stems from its use of eddy current damping, a passive electromagnetic phenomenon. As the magnetic assembly attempts to swing due to kinetic forces (turns, acceleration), its motion within the magnetic field of the damping mechanism induces small eddy currents in a conductive surface. By Lenz's law, these induced currents create a magnetic field that opposes the original motion, effectively arresting overswing without relying on viscous fluid drag. The magnetic sensing element utilizes a massive magnet to generate greater directive force from the Earth's horizontal magnetic field, further reducing the influence of mechanical forces and lowering the instrument's inherent error margin compared to the pendulous design of traditional wet compasses.
Note: The PAI-700-28V is a primary flight instrument. After installation, it is mandatory to perform a complete Compass Compensation (swinging the compass) procedure using the two internal compensator screws (N-S and E-W) to minimize the magnetic deviation caused by the aircraft structure. This must be done with the engine running and all normal electrical equipment (avionics, lights) operating. A deviation card must be installed in clear view of the pilot. Installation and compensation must be performed and certified by a licensed A&P mechanic or Avionics Technician in accordance with the PAI-700 Installation Manual and applicable FAA guidance.
Documentation
Authoritative documentation for this TSO component includes:
PAI-700 Vertical Card Compass Installation Manual (Instructions for Continued Airworthiness).
FAA Technical Standard Order (TSO) C7c Type 1.
Consult the aircraft's Maintenance Manual for compass location and magnetic clearance requirements.