THE HAGUE, Netherlands – A Dutch safety watchdog issued a warning Monday about a potential risk when planes using autopilot and an airport’s automated landing system approach a runway at too steep an angle.
The Dutch Safety Board said that airport Instrument Landing Systems can give planes flying on autopilot inaccurate information.
The board said that’s what happened during a May 31 incident at Eindhoven Airport in the Netherlands this year during which a plane narrowly avoided stalling just before landing.
The board’s warning, sent to aviation officials around the world, says that if a plane approaches a runway at greater than a three-degree angle, the airport system could tell the autopilot to raise the plane’s nose, increasing risk of a stall.
An antenna type called “M-array” was a common factor in three incidents the board analyzed — in Eindhoven and similar situations at Amsterdam’s Schiphol Airport in 2011 and at Charles de Gaulle Airport in Paris last year.
“The M-array ILS antenna type is used around the world,” the board said in its warning. It did not mention any manufacturers of such antennas.
The three incidents mentioned by the safety board and a test it carried out involved aircraft from four different manufacturers.
The board said that pilots should be aware of “the dangers accompanying flying in the area above the three-degree glide path during the approach” to landing.
“This is a pilot awareness issue and it is fixable,” said John Cox, an aviation safety consultant and former US Airways pilot. “I would call it a moderately big deal. It is something that needs to be out there and pilots need to be aware of it.”
The Dutch board said a wrong signal was sometimes present at a six-degree angle of decent and always at a nine-degree descent.
“It is very unusual to be that far off the glide slope,” Cox said.
The Dutch agency appealed to other operators to contact it if they believed a similar incident had happened on one of their flights.
AP Transportation Reporter Joan Lowy in Washington, D.C., contributed to this report.