A plane spotter doing some research in the regional airline neighborhood of a bustling commercial-service airport is likely to notice a sleek jet that looms larger than the 50-seat commuter aircraft with which it often shares gate space. With its two engines mounted beneath winglet-tipped, swept wings, Embraer’s E-170, a member of the Brazilian manufacturer’s Ejet family “looks and feels like a mainline aircraft,” its maker says. E-170s in service in the US Airways Express fleet seat 69 passengers, with nine seats in a first class section and 60 more in coach.