Was it all bureaucratic elements? Or were there other hiccups along the way?
Oh my, where to start
Boeing missed guarantees pretty badly on the initial 747-8. I've been through several programs over the years - usually we miss on something - weight, drag, or SFC - but exceed on at least one of the others and the result is we meet (or are at least close) on the final numbers. On the 747-8 we missed on all three
. So there has been an on-going effort since EIS to fix all three. We've cut out close to 10,000 lbs empty weight, there have been drag improvements, and the PIP was good for 2% in mission fuel burn and basically got us to what we originally promised for SFC.
The problem became, as soon as the operators learned of the PIP, they lost interest in taking new airplanes until we could give them the PIP. So the pressure was on to certify the PIP as soon as possible so that we could deliver airplanes. The result was we were given a schedule that we would have struggled to meet even if everything went perfectly. Then there were discoveries during flight test - nothing unusual that we couldn't readily fix - but it took time that wasn't in the schedule. Then the Ice Crystal Icing issue hit the fan, which turned into a major bureaucratic hurdle. The last couple months have not been fun
We saw ~2% mission fuel burn for the PIP, and we got some other small engine fuel burn improvements since EIS with various FADEC adjustments. I know there have been meaningful empty weight reductions, and we bumped the max TO weight by 10,000 lbs (didn't really require any real changes, just using margins that we weren't using), and there have been tweaks to the airplane to reduce drag. But I'm an engine guy - I don't know the details of how they figure a 10k increase in MTOW and a similar reduction in empty weight equates to a ~1.5% improvement in fuel burn.