The National Accountability Bureau (NAB) Khyber-Pakhtunkhwa has summoned Pakistan Tehreek-e-Insaf (PTI) Chairman Imran Khan in the helicopter scandal case on July 18.The anti-corruption watchdog's spokesperson Salma Begum told the media in a news conference on Thursday.NAB chief Javed Iqbal has given the green light to the appeal and an investigation into the matter is underway.Imran has been charged with the misuse of the K-P government's official helicopter for 74 hours causing a Rs2.17 million loss to the provincial exchequer.He would be grilled about the use of official chopper during the tenure of his party government in the province from 2013-18.The NAB has already recorded the statements of former K-P chief minister Pervez Khattak along with four senior bureaucrats including three administrative secretaries.Iqbal authorised a probe into the case following reports surfaced in the media.The helicopter was used by the former cricket star from Bani Gala to Kohat, Peshawar, Mardan, Batagram, Dir, Kumrat valley and other areas.