WICHITA, Kan. - A man accused of plotting a suicide bomb attack at a Wichita, Kansas, airport in 2013 pleaded guilty on Monday in US District Court to a charge of attempted use of a weapon of mass destruction.Terry Loewen, 59, was arrested trying to enter the tarmac at the airport with what he believed was a vehicle loaded with explosives, with a plan to trigger the device next to a terminal and die in the blast, according to a criminal complaint.A plea agreement calls for Loewen to be sentenced to 20 years in prison, followed by lifetime supervision. US District Judge Monti Belot set sentencing for Aug. 31."Terry Loewen utilized his privileged airport access to attempt a terrorist attack in Wichita," Assistant Attorney General John Carlin said in a news release. "Detecting, disrupting and holding accountable those who wish to harm Americans remains our highest priority."Loewen was indicted in December 2013 on three charges and told the court on Friday he planned to change his plea from not guilty.Charges of attempted use of an explosive and attempting to provide material support to a designated foreign terrorist organization were dropped under the agreement.Prosecutors said at the time of his arrest that Loewen, an aviation technician, had proclaimed himself Muslim and had talked of committing "violent jihad on behalf of al-Qaida."Loewen had a pass for security access to the Mid-Continent Airport, which is now called Wichita Dwight D. Eisenhower National Airport, and had been under investigation by a joint terrorism task force for months.The defendant believed he was working with a member of a Yemen-based militant group and another individual, both of whom were undercover FBI agents, a criminal complaint said.The agents helped Loewen with construction of the device, which was not active, the complaint said. Loewen left a letter for a family member describing his intent to conduct a martyrdom operation, it said.