It looks like you need to study AR 600-8-4. From AR 635-40:
3–4. Line of duty decisions
a.
Under the laws governing the Army PDES, Soldiers who sustain or aggravate physically unfitting disabilities must meet the following LD criteria to be eligible to receive retirement and severance pay benefits.
(1) The disability must have been incurred or aggravated while the Soldier was entitled to basic pay or as the proximate cause of performing active duty or inactive duty training (IDT).
(2) The disability must not have resulted from the Soldier’s intentional misconduct or willful neglect and must not have been incurred during a period of unauthorized absence.
b.
LD decisions are reached according to policies and procedures prescribed in AR 600–8–4. Copies of LD decision,
DA Form 2173 (Statement of Medical Examination and Duty Status), or DD Form 261 (Report of Investigation—Line of Duty and Misconduct Status) must be included in the official records of the case. When a board or council has substantial evidence, however, showing that a prior decision may be incorrect for any reason, they must include such
evidence in the case record and request U.S. Army Human Resources Command (AHRC–PDC–P), 1600 Spearhead Division Avenue, Fort Knox, KY 40122–5208 to review the LD determination before final disposition of disability processing at Headquarters, Department of the Army (HQDA) level (see para 4–19
c. In certain categories of activities, the deputy commander, PEB president, or alternate president have the authority to make findings of “in line of duty, not due to own misconduct” when no LD investigation has been completed and specific criteria have been met (para 4–19