The agency said air traffic controllers should wait to clear airplanes that are landings at airports until they clear other facilities in the vicinity and modify an altitude monitoring system to recognize deviations from established flight plans that were not previously entered.

The recommendations are the result of the agency’s investigation of a 2014 incident involving a Southwest Airlines flight that landed at the wrong airport in Missouri and a lesser known 2013 incident involving a smaller regional airline in Kansas. 

The Southwest flight, which was flying from Chicago's Midway Airport, was supposed to arrive at the Branson, Mo., airport. But instead, it touched down at the nearby Taney County airport.

The NTSB said the air traffic controllers who were directing the plane should have warned pilots about proximity of the two airports as they were coming in for a landing.
 
“The controller in the Southwest Airlines flight 4013 event did not provide the location of the nearby airport that could have potentially caused confusion,” the agency said.

“While the controllers should have provided the locations of the airports that could potentially cause confusion and the pilots should have more closely monitored their flightpaths relative to the intended destination airports, these events suggest that the issuance of a landing clearance to the pilot far away from the destination airport and with the destination airport in close proximity to other airports exacerbates the potential for human error,” the agency continued.

The NTSB said later landing clearances would prevent the possibility of confusion among pilots who are entering unfamiliar airspaces.

“The NTSB acknowledges that flight crews need to remain vigilant and ensure that they are landing at the correct airport,” the agency said. “However, the NTSB concludes that issuing a landing clearance for an aircraft to land at an airport when it has not yet passed other nearby airports may confuse pilots, particularly when executing a visual approach, and amending air traffic control (ATC) procedures could provide another measure of protection to avoid wrong airport landings. Therefore, the NTSB recommends that the FAA amend ATC procedures so that controllers withhold landing clearance until the aircraft has passed all other airports that may be confused with the destination airport.”

The NTSB also placed blame for the wrong airport landings on flaws with an altitude monitoring system known as Minimum Safe Altitude Warning Software.

The agency said the software automatically changed the flight path of the planes that ended up at wrong airports when they began their descent, preventing pilots from receiving a warning that they were attempting to land too soon.

“Regarding the Atlas Air flight 4241 event, the flight crew failed to correctly identify the destination airport and complete the RNAV approach to runway 19L at IAB in compliance with the ATC clearance,” the NTSB said.

“Instead, the flight crew effectively executed a visual approach to AAO after misidentifying AAO as their destination of IAB,” the agency continued. “Review of MSAW software showed that in circumstances such as this, the MSAW software automatically treats aircraft within the MSAW eligibility area for an airport as arrivals to that airport. Consequently, even though Atlas Air flight 4241 was incorrectly descending several miles before its planned destination of IAB, the MSAW software assumed that the airplane was intentionally landing at AAO and did not warn the IAB tower controller of the airplane’s premature descent.”

The NTSB said the altitude monitoring system should be amended to only deviate from established flight plans when destinations are manually changed.

“The NTSB concludes that the current MSAW software design, allowing an aircraft’s flight-planned destination to be automatically changed to a different airport based on an observed trajectory, renders MSAW less effective at providing a warning when an aircraft’s altitude falls below its intended flightpath, which is likely to occur when an aircraft executes an approach at the wrong airport,” the agency said. “If the MSAW software uses the destination airport in the current flight plan (unless the destination information is amended by ATC), the MSAW software would provide timely alerts to ATC to provide sufficient time for controllers to intervene and help prevent wrong airport landings.” （By Keith Laing）