OTTAWA - Another Conservative cabinet minister is under fire for failing to report air travel in his ministerial expenses.

Transport Minister Lawrence Cannon made regular use of a government executive jet last year while keeping the trips off his travel expenses, documents show.

He's the second minister this week to have his travel habits exposed using government documents obtained by the NDP through an Access to Information Act request.

It's an embarrassing lapse of transparency for a government in the midst of trumpeting new accountability legislation in the House of Commons.

Transport Canada's aircraft flight log shows at least six trips taken by Cannon in 2006 aboard a sleek Citation C-550 executive jet that do not appear in his ministerial expenses posted on the department's website, as mandated by the federal Treasury Board.

Transport Department officials could not immediately say how much it costs the department to operate the Citation C-550s, but Defence Department documents show the executive Challenger jets cost about $9,000 an hour.

"It looks to me like the government is trying to obfuscate the situation,'' said NDP Leader Jack Layton.

"What they should be doing is trying to make it very clear what money is being spent when cabinet ministers travel. We have nothing against cabinet ministers travelling. What we don't like is them trying to hide the costs.''

Cannon's officials are adamant that nothing was "hidden.'' The proof, they said, is that they provided details of the six missing trips upon request by The Canadian Press.

But that request came solely as a result of the internal aircraft logs obtained by the NDP, which alone revealed Cannon's travel.

Cannon's office listed specific ministerial duties on all the flights, but said they weren't proactively disclosed because they were considered department business.

"(Treasury Board) guidelines do not require the minister to divulge the cost of its travel if the travel is not paid by his budget,'' press secretary Natalie Sarafian said in an e-mail.

It's the same rationale used by Labour Minister Jean-Pierre Blackburn this week to explain away $150,000 in undisclosed charter flights.

But the Treasury Board rules state ministers must disclose on their websites "all travel expenses incurred on program-related business,'' including fees for commercial carriers, fees for privately owned, government-owned or rental vehicles, and fees for the rental of trains, planes or marine transport.

Catherine Loubier, Cannon's communications director, confirmed there is no distinction between "program-related business'' and departmental business.

But she said the minister can't claim for costs incurred by the department. If the Transport Canada flight was the only expense for the minister's trip, he has nothing to declare, said Loubier.

"We have nothing to hide. This is public information.''

The explanation left observers scratching their heads.

"A minister is responsible for his department and should be declaring all of the expenses associated with his travel,'' said Layton. "This is a party that ran on the principle of transparency and openness.''

The minority Tories rode to power last year on a platform of instilling accountability in government, but may be finding this easier said than done.

"If they are spending money in legitimate, appropriate, proper ways, they have nothing to fear from disclosing it,'' said Arthur Schafer, director of the Centre for Professional and Applied Ethics at the University of Manitoba.

"What they have to answer is: if it is appropriate, why are you hiding it?''

Blackburn appeared non-plussed this week when another NDP access request revealed $150,000 in charter flights last year for which he had not filed expenses.

Like Cannon, Blackburn's explanation was that his travel should be paid for by the department, not counted as a ministerial expense.

The government also falsely claimed Blackburn's air travel was openly posted on the departmental website. In fact, Blackburn's air charter bills were scattered among hundreds of other departmental contracts, with no names or destinations attached, making the posted information virtually meaningless.

As with Cannon's lost travel, no public observer could possibly connect the dots on the ministerial flights without obtaining the internal flight logs.