Last week, I wrote about Boeing's decision to ramp up 737 output to 52 per month in 2018. I sounded a cautionary note about long-term overcapacity, particularly if Airbus matches Boeing. But I'm starting to think there's no reason to worry; this announcement is far from certain to be executed. Consider the factors that could derail the ramp up: First, we're talking about 2018. A lot can happen in four years. Over the past five years, single aisle production has been massively increased by a combination of three factors: low interest rates, expensive fuel (which makes new jets more appealing than keeping or buying cheap older ones), and fast growth in emerging markets (primarily the BRICs).