Members of City Council on Friday grilled Philadelphia Parking Authority officials over why revenue from a 50-cent-per-hour parking-rate increase never made it to the Philadelphia School District as promised.

The parking authority estimated that the 2014 increase would result in an additional $7.5 million for the district. Instead, the school district's contributions from the parking authority decreased from $13.2 million in fiscal year 2012 to an estimated $8 million in 2017.

"I'm just curious about why you were so far off in those projections," Councilwoman Helen Gym said.

Gym said she had "serious concerns" about the authority's ability to do accurate long-term fiscal planning.

Authority officials said contributions to the district dropped because of factors outside their control, such as rising pension costs and lost parking revenue from snowstorms and major events such as last year's papal visit.

"We came in and gave you honest information on what we reasonably believed would happen," said Richard Dickson, the authority's deputy executive director.

The parking authority, which employs about 1,000 people and is controlled by the state, already was facing heat this week after it was reported that state legislation to regulate ride-sharing services such as Uber and Lyft had been amended in a way that would result in less money - and maybe none at all - for the school district.

Council members used Friday's hearing to take a broad look at the PPA's financial operations, questioning how the agency spends its approximately $240 million annual budget and whether operating costs are cutting into revenue for the city and schools.

Dickson said the formulas used to disburse parking revenue were set by law. And he said authority staff meet with staff from the city's finance office every other month to ensure the accuracy of their financial statements.

City Finance Director Rob Dubow testified that he believed that the authority's numbers were accurate and that officials were allocating what is required to the city and school district. Dubow called an audit of the parking authority "not a bad idea," given that the most recent one was done in 2009.

Several Council members said they, too, thought a PPA audit would be a good idea.

In one of the few discernible moments of progress during the hearing, Dubow and Vince Fenerty, the PPA's executive director, agreed school district staff also should be at the table for the every-other-months financial meetings, and will be invited going forward.

That came as a relief to Uri Monson, the district's chief financial officer, who testified that he is frustrated about a lack of communication between the authority and district. For example, he said he learned just a few weeks ago - from a news article - that the PPA planned to reduce its payments to the school district for 2017 by $3 million.

"I'm looking forward to attending those meetings and being able to ask questions," Monson said.