GPPB NPM 047-2007 answers the said question, to wit:
Issues Concern: Qualification of the Chairman of the Bids and Awards Committee
DETAILS
Whether the designation of the OIC of the Administrative Division as BAC Chairman is in accordance with the provisions of R.A. 9184 and its IRR-A.
For agencies, departments, bureaus, offices or instrumentalities of the National Government, the BAC Chairman should be at least a third ranking permanent official (Section 11.2.1, IRR-A). The term “permanent” refers to a plantilla position within the procuring entity concerned (Ibid.). According to the Personnel Services Itemization of the DBM, plantilla refers to the list of positions authorized to be created by the DBM (GPPB NPM Opinion No. 18-2006 dated 08 November 2006). The term “permanent” does not refer to whether the person holding the plantilla position is contractual, regular, designated or appointed; rather, it is whether said position is included in the list of authorized positions created by DBM or existing within the organizational structure of the procuring entity (GPPB NPM Opinion No. 025-2004 dated 08 March 2004).
Based on the foregoing, any person holding a position existing within the organizational structure of the procuring entity and who possesses the required ranking may be designated as BAC Chairman. The determining factor for regular membership in the BAC is not the employment status of the person but the position he is holding (Ibid.).
[Thus,] notwithstanding [the] employment status as OIC of the Administrative Division, as long as such position is considered as a third ranking position in the approved organizational structure, [the personnel] may be validly designated as BAC Chairman.