However, our appellate court has held that section 6-110's definition "applies equally to all firefighters" in Illinois. Mabie v. Village of Schaumburg , 364 Ill. App. 3d 756, 759, 301 Ill.Dec. 786, 847 N.E.2d 796 (2006) ; Jensen v. East Dundee Fire Protection District , 362 Ill. App. 3d 197, 204, 298 Ill.Dec. 347, 839 N.E.2d 670 (2005). ¶ 40 To recover a line of duty disability pension, a claimant need not prove that his job duties were the "sole or even the primary cause" of his disability"; rather, it is sufficient that an act of duty was an "aggravating, contributing or exacerbating factor" in the ensuing disability.

There is no definition of "act of duty" in the section of the Pension Code applying to firefighters in municipalities with populations of 500,000 and under. However, this court has held the definition in the Pension Code for cities with populations over 500,000 applies equally to all firefighters. See Jensen v. East Dundee Fire Protection District Firefighters' Pension Fund Board of Trustees, 362 Ill. App. 3d 197, 204, 839 N.E.2d 670 (2005). That section defines an "act of duty" as:

Merlo, 383 Ill. App. 3d at 99. ¶ 18 The parties agree that the question presented here is a mixed question of law and fact, i.e., "an examination of the legal effect of a given set of facts." Jensen v. East Dundee Fire Protection District Firefighters' Pension Fund Board of Trustees, 362 Ill. App. 3d 197, 202 (2005). We agree and will therefore apply the clearly erroneous standard when reviewing the Board's ultimate decision.

However, section 4-110 does not define "act of duty."¶ 34 In Jensen v. East Dundee Fire Protection District Firefighters' Pension Fund Board of Trustees, 362 Ill. App. 3d 197 (2005), the Board denied the plaintiff-firefighter a line-of-duty disability pension. On review, the appellate court determined that the Board erred by applying section 5-113 of the Code (40 ILCS 5/5-113 (West 2004)), defining an act of duty applicable to police officers, rather than section 6-110 of the Code (40 ILCS 5/6/110 (West 2004)) applicable to firefighters.

For purposes of determining the right to a line-of-duty disability pension under section 4-110, courts apply the definition of "act of duty" set forth in section 6-110 of the Code ( 40 ILCS 5/6-110 (West 2004)). Jensen v. East Dundee Fire Protection District Firefighters' Pension Fund Board of Trustees, 362 Ill. App. 3d 197, 203-04 (2005). Under section 6-110, "act of duty" means "[a]ny act imposed on an active fireman by the ordinances of a city, or by the rules or regulations of its fire department, or any act performed by an active fireman while on duty, having for its direct purpose the saving of the life or property of another person."

See Jensen v. East Dundee Fire Protection District Firefighters' Pension Fund Board of Trustees, 362 Ill.App.3d 197, 203-04 (2005). Under that definition, an "act of duty" includes any act that is (1) "imposed on an active fireman by the ordinances of a city, or [(2)] by the rules or regulations of its fire department, or [(3)] any act performed by an active fireman while on duty, having for its direct purpose the saving of the life or property of another person."

We will reverse and remand for a new hearing if we find that the agency applied the wrong legal standard. See Jensen v. East Dundee Fire Protection District Firefighters' Pension Fund Board of Trustees, 362 Ill. App. 3d 197, 204-05 (2005).¶ 19 Interpreting an ASO is a question of law. O'Connor, 2018 IL App (1st) 171930, ¶ 16.

Prawdzik v. Board of Trustees of the Homer Township Fire Protection District Pension Fund , 2019 IL App (3d) 170024, ¶ 40, 430 Ill.Dec. 304, 126 N.E.3d 392 ; Scepurek v. Board of Trustees of the Northbrook Firefighters' Pension Fund , 2014 IL App (1st) 131066, ¶ 27, 379 Ill.Dec. 753, 7 N.E.3d 179 ; Village of Oak Park v. Village of Oak Park Firefighters Pension Board , 362 Ill. App. 3d 357, 371, 298 Ill.Dec. 235, 839 N.E.2d 558 (2005). ¶ 46 Although section 4-110 (which governs duty pensions for firefighters in smaller municipalities like the Village) does not define the term "act of duty," courts have held that it means the same thing as "act of duty" as defined in section 6-110 ( 40 ILCS 5/6-110 (West 2018) ), a companion statute governing duty disability pensions for firefighters in large cities. Jensen v. East Dundee Fire Protection District Firefighters' Pension Fund Board of Trustees , 362 Ill. App. 3d 197, 203-04, 298 Ill.Dec. 347, 839 N.E.2d 670 (2005). Under that definition, an "act of duty" includes (1) "[a]ny act imposed on an active fireman by the ordinances of a city," (2) any act imposed "by the rules or regulations of its fire department," or (3) "any act performed by an active fireman while on duty, having for its direct purpose the saving of the life or property of another person."

¶ 26 We find that our review involves a mixed question of law and fact, as we must examine the legal effect on a given set of facts, i.e., whether SIU violated section 14(a)(1) of the Act when it did not answer petitioner's September 14, 2016, request for an informal grievance meeting under section 6.03 of the CBA. See Jensen v. East Dundee Fire Protection District Firefighters' Pension Fund Board of Trustees, 362 Ill. App. 3d 197, 202 (2005) (stating that when a case involves "an examination of the legal effect of a given set of facts" it involves a mixed question of law and fact); Parikh v. Division of Professional Regulation of Department of Financial & Professional Regulation, 2014 IL App (1st) 123319, ¶ 19 ("[m]ixed questions of fact and law 'are questions in which the historical facts are admitted or established, the rule of law is undisputed, and the issue is whether the facts satisfy the statutory standard,' or to put it another way, whether the rule of law as applied to the established facts is or is not violated") (quoting Pullman-Standard v. Swint, 456 U.S. 273, 289 n.19 (1982)). We will therefore apply the clearly erroneous standard.

More specifically, the issue is whether it was against the manifest weight of the evidence for the Board to find that the February 6, 2015, injury did not aggravate a preexisting physical condition, thereby barring claimant from a "line-of-duty" pension.¶ 24 On appeal, we review the decision of the administrative agency, not that of the circuit court. Jensen v. East Dundee Fire Protection District Firefighters' Pension Fund Board of Trustees, 362 Ill. App. 3d 197, 202 (2005). It is not the duty of the reviewing court to reweigh evidence, but rather it is the court's duty to ascertain whether the findings and decision of the administrative agency are against the manifest weight of the evidence.