A 21-year air traffic controller responsible for the improper arrival of Michelle Obama's VIP Boeing 737 flight into Andrews Air Force Base near Washington on 18 April had accumulated four operational errors involving "coordination errors" in the previous four years, says the US National Transportation Safety Board.
In a just released factual report on incident, classified as an operational error, NTSB says the controller, who had been certified by the FAA at the nearby "Mount Vernon area" air traffic control sector in 2007, violated at least two standard procedures for arrivals at the airport for the Obama flight.
After his earlier series of coordination errors at the Potomac consolidated terminal radar approach control, the controller had been decertified but was later re-certified after training.
On 18 April, the controller had vectored Obama's 737 on to the approach for runway 19L at the airport behind an Air Force C-17 four-engine cargo transport. Designated as a "heavy" aircraft, the C-17 requires in-trail aircraft the size of a 737 to be at least 5nm behind due to the possibility of wake turbulence upsets. At its closest, the 737 was 2.81nm behind the C-17, says the NTSB.
"He declared that he confused the minimum wake turbulence separation requirements for a B737 following a heavy C-17 as four miles instead of the required five miles between aircraft," the NTSB says. "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 separate the two aircraft enough so that the C-17 would be able to 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 were approved", says the NTSB.
While pilots under visual flight rules often use S turns (left and right turns along the approach course that increase the time it takes to get to the runway threshold), the NTSB notes that the practice is not authorised for an aircraft flying an approach under instrument flight rules, which applied to the 737 despite the visual weather 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.
The US Federal Aviation Administration later in April issued instructions requiring controllers in sectors handling the presidential flights to "aurally and visually monitor" the flights to ensure "separation, control, and coordination".