The 88731-701 is a Piper OEM left-hand (LH) wing main spar reinforcement kit used under Piper Service Bulletin 1372 as part of a structural inspection and reinforcement program for certain Piper PA-series aircraft.

This kit is installed on the left wing main spar assembly and is designed to reinforce the existing spar structure, improving fatigue resistance and extending service life of the wing structure when installed in accordance with approved maintenance data.

It is not a single part, but a structural modification kit, typically including reinforcement plates, attachment hardware (bolts, nuts, washers), and installation instructions required to perform the approved modification. It is used when inspection results or service bulletin compliance criteria indicate reinforcement is required or beneficial.

The wing spar is a primary load-bearing structure that carries aerodynamic loads from the wing into the fuselage. Because of this, any modification to the spar is considered a major structural repair/modification, requiring strict adherence to Piper engineering instructions and regulatory maintenance procedures.

According to Piper SB 1372, the reinforcement kit may be installed after inspection and within defined service life limits, and is part of a broader inspection and fatigue management program for wing spar longevity.

Key features include:

Piper 88731-701 LH wing spar reinforcement kit
Used for structural reinforcement of main wing spar (left wing)
Part of Service Bulletin 1372 compliance program
Includes reinforcement structure and installation hardware
Designed to improve fatigue resistance and extend spar service life
Installed on primary wing load path structure
Requires strict compliance with Piper maintenance instructions
Must be installed after approved inspection per SB requirements
Critical structural modification affecting airworthiness
Paired with RH kit 88731-702 for full wing application