AerCap shares opened up by 18 per cent in New York yesterday, after the Dublin-based aircraft lessor announced its results for the first quarter of the year.  Covid-19 has hit AerCap harder than other aviation companies. In the three weeks after 20 February it fell by 76 per cent — even more than the JETS ETF of major airlines, which fell 55 per cent.  Now, AerCap has made up some ground. After yesterday’s results, and the stock rally over the last month, AerCap and the JETs index are both down by about the same amount.  Why did AerCap take such…