US Republican presidential candidate and GoP frontrunner Donald Trump has been flying across the US aboard his Cessna 750, which is reportedly not registered to fly. Trump's private jet has been used by the 69-year-old to make several campaign stops, even as its registration expired in January this year.

According to a New York Times report, the US Federal Aviation Administration (FAA) has confirmed that the registration of Trump's private jet is yet to be renewed. The real estate mogul's company was reportedly sent a warning in December to renew the Cessna's registration, after which the company received a final notification in March.

Spokeswoman for the Trump campaign, Hope Hicks, told the New York Times that the registration renewal process for the aircraft was "just about complete". However, the FAA had reportedly not received an application for the renewal process.

Flying an unregistered plane in the US can result in a heavy penalty. The FAA could fine the owner as well as the operator and in the event of an accident, the insurance company could refuse any claims, citing the lapsed registration. The maximum penalty for flying an unregistered plan can go up to $250,000 and a prison term of up to three years.

Nonetheless, Trump's travel plans are unlikely to be hindered even if the FAA does ground his Cessna, as he also owns a Boeing 757 and three helicopters. In fact, Trump's Boeing, which has the trademark surname printed in gold-plated fittings, has been used in his campaign as a backdrop, to help stress and project the image of wealth. But, given the weight and size of the 757, there may be issues with landing the aircraft on smaller airports.