The improper handling of a VIP Boeing 737 carrying President Obama's wife, Michelle, into Andrews Air Force Base was the responsibility of a 21-year-old controller who had accumulated four operational errors in the previous four years.
In a newly-released factual report on the 18 April operational error, the US National Transportation Safety Board (NTSB) said the controller violated at least two standard procedures for arrivals at the airport.
After earlier co-ordination errors at the Potomac consolidated terminal radar approach control, the controller had been decertified but was later re-certified after training.
He had vectored Obama's 737 to the approach for runway 19L, behind a US Air Force Boeing C-17 transport. Designated as a 'heavy' aircraft, the C-17 requires separation of 5nm for in-trail aircraft the size of a 737. At its closest, the 737 was 2.81nm behind the C-17, says the NTSB.
"[The controller] declared that he confused the minimum wake turbulence separation requirements for a 737 following a heavy C-17 as four miles instead of the required five miles between aircraft," the NTSB said.
"The controller stated that he was thinking of 757-following-757 separation at Washington Reagan National airport and confused the two applications during this incident."
In an attempt to ensure the C-17 would exit the runway before the 737 crossed the threshold, as required by regulation, the controller further ignored procedures by advising the 737 pilot that S-turns - alternate left and right manoeuvres to increase the time to reach the runway - "were approved", added the NTSB.
It noted that the practice is not authorised for aircraft flying an approach under instrument flight rules, which applied to the 737 despite visual conditions at the time. The 737 pilots performed one S-turn but ultimately abandoned the approach for spacing, returning for a safe landing to the same runway.
Later in April, the US Federal Aviation Administration instructed controllers in sectors handling presidential flights to "aurally and visually monitor" the flights to ensure "separation, control, and co-ordination".