Mell, father-of-three, was accused of committing sex acts with a 15-year-old girl (Representational)

A 53-year-old millionaire trader could get five-year jail term after pleading guilty to engaging in sex acts with a 15-year-old girl, once even putting his private plane in autopilot mode for the purpose.

Stephen Bradley Mell, 53, of Bedminster, New Jersey, pleaded guilty to federal charges of engaging in interstate travel to engage in illicit sexual conduct and receiving child pornography in December 2018 and is now due for sentencing on Tuesday.

Mell, a father-of-three who had a brokerage firm, was accused of committing sex acts with a 15-year-old girl whose mother had approached him so that he could give her flying lessons, the Daily Mail reported.

Ahead of his sentencing, Mell's legal team has argued he is a 'humble man' who was on 'multiple anti-depressants' after falling into 'a spiral of depression' brought on by survivors' guilt over giving up his seat on a fatal helicopter trip with friends in 2012.

Mell also faces sentencing in July on a state charge related to sexual activity with the teen, which he pleaded guilty to earlier this month.

Mell started his own charity, Air LifeLine, which flew children with medical needs anywhere in the US for treatment.