WASHINGTON - Air traffic controllers mistakenly told the pilot of a plane carrying US first lady Michelle Obama this week he was further away from a nearby military cargo jet than he actually was, according to a report issued on Friday.

The National Transportation Safety Board's preliminary report provided new details on Monday's incident near Andrews Air Force Base outside Washington. The incident led to more criticism of US air traffic controllers following disclosures in recent weeks that several had fallen asleep on the job.

Air traffic controllers at the Maryland base told the pilot of the US government Boeing 737 carrying the first lady that he was 4 miles (6.4 km) from a giant Air Force C-17 cargo when he was in fact 3 miles (4.8 km) away, the NTSB report found.

Related readings:  Plane with first lady came too close to cargo jet

The report said the controllers then instructed the pilot of the first lady's plane to do a maneuver that actually brought the Boeing 737 closer to the C-17, not further away from it. The report said the first lady's plane came as close as 2.94 miles (4.7 km) to the cargo plane, slightly closer than the 3 miles (4.8 km) previously acknowledged by officials.

Michelle Obama's plane also was carrying Jill Biden, wife of Vice President Joe Biden, on a trip from New York.

The plane was forced to abandon a landing approach outside Washington to avoid the C-17, one of the largest planes in the skies. The C-17 was also heading to Andrews. Both planes landed safely without incident.

The Federal Aviation Administration (FAA), which oversees the nation's 15,000 controllers handling flights in and out of more than 400 airports, had no comment on the NTSB report.

In another development, the union representing air traffic controllers issued a statement on the controversy involving sleeping controllers.

The National Air Traffic Controllers Association said the FAA has ignored "common sense solutions" developed in consultation with the military and NASA for reducing fatigue. It also called on Congress to approve fatigue management provisions in pending aviation legislation.

"Air traffic controllers are committed to doing their part to ensure safety and fix the problem," the union said.

The FAA has already adjusted scheduling practices and added staff on late shifts to reduce fatigue.