The race to become the first Western air-taxi company to carry passengers lost a high-profile competitor this month when Germany's Lilium succumbed to a cash crisis, throwing a fresh spotlight on a major hurdle for the fledgling industry. Almost half-way into the decade in which air-taxi makers have promised investors the first commercial flights, the company's demise shows how dwindling cash balances threaten to delay the sector's aim to revolutionise urban travel. Makers of electric vertical