ANS: Yes, you would collect the Defined Benefit Plan (DBP or "A" Plan "Pension") as defined in the Collective Bargaining Agreement in Article 15 of the UPS/IPA "contract" if you are vested.
Vesting : "Crewmembers shall be fully vested after completing one (1) vesting year. For purposes of this section, vesting years will be counted from the crewmember’s initial date of hire with the Company.
A vesting year for the purpose of this section shall be the first twelve (12) months of employment provided the crewmember completes 750:00 hours of service in such twelve (12) month period.

Each Pay period is a minimum of 75 hours credit, 13 per year, so can achieve in first year of employment for early classes, and if hired later in the year, will be vested in the second calendar year of employment (usually still in the first 12 months of employment) but the next calendar year.
example: Hired Jan 2017, will be vested by end of 2017. Hired October 2017, will be vested by end of 12 months (normal case) and be vested in 2018.
You can leave at any time and will keep your earned DBP. Early retirement is age 55 and normal retirement is 60.