The 487-351 is a Piper airframe spring used in the seat back adjustment mechanism, specifically identified as the inboard seat back adjustment spring. It is part of the pilot or passenger seat assembly that allows controlled adjustment of the seat back angle and ensures secure locking in the selected position.

In Piper light aircraft (commonly PA-series models such as Archer, Warrior, and Arrow variants depending on configuration), the seat back adjustment system uses paired springs—an inboard (487-351) and an outboard (487-352)—to provide balanced tension across the seat frame. The inboard spring is mounted on the inner side of the seat structure, working in conjunction with the outboard spring to maintain symmetrical force distribution during adjustment and operation.

This spring provides return force and preload tension for the seat back locking mechanism, ensuring that the seat remains firmly engaged in the selected detent position even under vibration, pilot movement, and operational loads during flight and ground operations. It also contributes to smooth adjustment motion when changing seat back angle.

Because it operates under repeated loading cycles, the 487-351 is subject to fatigue over time. Wear, corrosion, or loss of elasticity can lead to uneven seat resistance, reduced locking security, or inconsistent adjustment behavior. For this reason, it is typically inspected during seat maintenance, upholstery work, or scheduled airframe interior checks.

Key features include:

Piper 487-351 seat back adjustment inboard spring
Used in pilot/passenger seat recline adjustment mechanism
Provides tension and return force for seat locking system
Works in matched pair with outboard spring 487-352
Installed on inboard side of seat frame assembly
Material: high-strength spring steel designed for cyclic loading
Ensures secure seat back positioning under operational vibration
Supports smooth and balanced seat adjustment movement
Common in Piper PA-series aircraft seating systems
Typically replaced during seat overhaul or interior refurbishment