Given Senator John McCain’s signature stance on campaign finance reform, it was not surprising that he backed legislation last year requiring presidential candidates to pay the actual cost of flying on corporate jets. The law, which requires campaigns to pay charter rates when using such jets rather than cheaper first-class fares, was intended to reduce the influence of lobbyists and create a level financial playing field.

But over a seven-month period beginning last summer, Mr. McCain’s cash-short campaign gave itself an advantage by using a corporate jet owned by a company headed by his wife, Cindy McCain, according to public records. For five of those months, the plane was used almost exclusively for campaign-related purposes, those records show.

Mr. McCain’s campaign paid a total of $241,149 for the use of that plane from last August through February, records show. That amount is approximately the cost of chartering a similar jet for a month or two, according to industry estimates.

The senator was able to fly so inexpensively because the law specifically exempts aircraft owned by a candidate or his family or by a privately held company they control. The Federal Election Commission adopted rules in December to close the loophole  rules that would have required substantial payments by candidates using family-owned planes  but the agency soon lost the requisite number of commissioners needed to complete the rule making.