THE METROPOLITAN Washington Airports Authority (MWAA), which manages Washington Dulles and Reagan National airports and, critically, construction of Metro’s $6 billion Silver Line extension to Dulles, is an odd hybrid: an independent body, overseeing major publicly owned assets but nonetheless subject to few federal and state laws. That’s why it’s crucial that the MWAA maintain and observe muscular internal ethics policies.

Unfortunately, the authority has failed to do so. It has functioned with slapdash procedures governing contracting and hiring, both of which have been subject to a culture of cronyism and favoritism. Its ethical rules have been ignored. Not infrequently, business travel has been treated as a boondoggle.

The authority’s board of directors, which sets the tone and direction for the MWAA, deserves particular blame. For years, board members treated the authority as a high-end travel agency, using it to attend conferences and eat and drink lavishly. A number of them were then rewarded with insider contracts upon leaving the board. The example they set infected the authority as a whole.

Such shabby practices have now been detailed in a thorough audit by the Transportation Department’s inspector general. The audit report confirms, amplifies and adds reams of detail to what was known — thanks partly to a preliminary report last spring — about the authority’s deep-rooted problems. It makes an irrefutable case for urgent reform.

The MWAA and its 1,400 employees are not going away. Under its lease with the federal government, it will run the airports for the next half-century. But without a top-to-bottom house-cleaning, the authority will encounter gale-force political head winds that will jeopardize its ability to do that job and build rail to Dulles. Already, there have been calls in Congress and Richmond to remove it from overseeing the Silver Line project.

Fortunately, the authority’s leaders, including board Chairman Michael Curto and chief executive Jack Potter, understand the stakes. Both are relatively new in their jobs; neither contributed to the MWAA’s problems.

They have begun to implement tighter policies and procedures, starting with new rules governing ethics and travel. Much more must be done. The authority should hasten to endorse and adopt the auditor’s recommendations, especially on contracting. These include offering a special measure of transparency to practically every dollar the authority spends. That may seem like an extraordinary burden, but the authority has brought this on itself.