The Philadelphia Police Department was in the news for the wrong reasons again this week. For the second time in recent years, the credibility of several officers assigned to its narcotics unit was called into question. They were alleged to have switched sides and "partnered with drug dealers."

Charges have been or are expected to be dropped in more than 100 drug cases so far, and the District Attorney's Office has said it won't use the officers as witnesses in any further narcotics prosecutions. Given that the officers have been involved in narcotics cases since at least 2006, the number of cases and convictions affected could reach staggering numbers. The city could be in for another round of embarrassing revelations that may dwarf the fallout of the drug enforcement scandal of a few years ago, which forced the city to pay out millions to those falsely arrested by rogue officers.

The embarrassments haven't been limited to the narcotics unit. A multitude of headlines suggest the department is dealing with more than a few isolated incidents.

Another recent scandal in the firearms unit spread to internal affairs after allegations of stolen weapons and a cover-up. And more than 50 members of the department have been arrested on an array of charges over the past three years: drunken driving, theft, extortion, and even murder.

So is there a systemic problem in the Police Department? Given the number and extent of recent scandals, it appears that the problem is at least partly institutional.

Under such circumstances, the best course is to give an outside entity power to examine the agency and recommend ways to fix what ails it. Mayor Nutter should appoint a commission with broad authority to delve into the inner workings of the department to correct its institutional failings.

Commissions examining police departments are about as old as modern policing. Unfortunately, they go hand in hand. Barely a major police department has been spared such an examination. That includes Philadelphia, which has needed such oversight before and needs it again today.

The most famous such study of a wayward police department was by New York's Knapp commission, formed in 1970. Corruption in the New York City Police Department at the time was rampant and readily apparent to many a casual observer. But the department's officers didn't see it that way; to them, it was just the way the NYPD operated. In retrospect, many officers who were against the commission came to conclude that it was necessary to change the department's culture.

The goals of a commission should be twofold: First, flush the poison out of the system. The public must have confidence in the police, and that trust is lacking. Next, reenergize the agency and restore its pride. Remind the officers why they joined in the first place and make those values the focus of their work going forward.

The Philadelphia police's problems may not be as great as the NYPD's or their own of yesteryear, but there's no reason to wait for them to metastasize until they reach that point. There is virtue in acknowledging the problem head on and attacking it rather than waiting for it to get worse.

The Philadelphia Police Department says it aspires to be a "model of excellence," and many of its members are. But there is an undercurrent detracting from their good work that needs to be addressed. A commission is the best way.