Sergey Petrossov launched JetSmarter, the Uber for private jet travel in 2013. In April 2018, JetSmarter was valued at $1.5 billion and had 15,000 subscribers paying at least $5,000 a year to book flights on private jet. Today, the company is mired in lawsuits and worth about a fifth of that $1.5 billion. It’s 30-year-old founder is scrambling to explain himself.