In Washington, it is rare when a public official actually tells the truth. But recently, the nation's top aviation medical official, James Fraser, courageously acknowledged the truth behind the "cargo carve-out," a rule allowing exhausted cargo pilots to fly when safety rules would ground other commercial pilots. We owe him a debt of gratitude for letting us see how Washington really works.

At the Air Line Pilots Association's Air Safety Forum last month, Fraser, the Federal Aviation Administration's chief air surgeon, said the FAA's exclusion of cargo pilots from new fatigue rules was done for political reasons. Fraser said the aviation professionals at the FAA understand that there is no difference between pilots who fly cargo and pilots who carry passengers, other than the fact that cargo carriers' management complained that increased rest for pilots would cost too much.

"I'm going to leave that for the political arena," Fraser said, "and just tell you that it's not those of us that are in the trenches at FAA headquarters that are against (including cargo pilots under the rule). It's a political issue in terms of the cost of making those changes for cargo pilots."

In Washington, they say you should always "follow the money." The trail is obvious: UPS and FedEx, the nation's largest cargo airlines, have spent more than $140 million in lobbying and political contributions since President Obama took office. Small wonder that this administration carved cargo pilots out of the rule.

The FAA's new pilot fatigue rules, enacted in January, were the first major revisions to pilot flight and duty limits in 60 years. They are based on modern knowledge of the effects of sleep and circadian rhythm on the human body. Cargo pilots were included when the regulations were proposed by the FAA, but the White House ordered the agency to remove them. This despite the fact that cargo airlines use the same aircraft as passenger airlines, take off and land on the same runways and fly the same jet routes as all of us.

Just days ago, the National Transportation Safety Board reported the findings of its investigation into the 2013 crash of a UPS cargo plane in Birmingham, Ala., which killed two crew members. The NTSB, in part, blamed pilot fatigue for the crash. The cockpit voice recorder captured the plane's crew discussing how tired they were just before the doomed flight took off.

As a result of the investigation, the NTSB took some minor steps to increase communication about fatigue between crew members. That's far from enough.

Millions of Americans who fly, and the many more who live under the flight paths of cargo airliners, are threatened by the effects of fatigue. If the FAA is unwilling or unable to resist the political pressure to keep its fatigue rules from applying to all pilots, including those from cargo airlines, then Congress needs to step in to restore one level of safety to our skies.

Jim Hall, a former chairman of the NTSB, is president of Hall & Associates. Peter Goelz, a former NTSB managing director, is a principal at O'Neill & Associates.