Originally Posted by
meh130
... back in the 1960s, when designing pretty much any airliner, the engineers' solution was to over-engineer the aircraft. ... Since then, engineers design assuming a fixed lifetime, and seek to save weight where ever possible.
cheap gas, and the absence of really detailed life-cycle-cost analyses, drove a lot of design philosophies and associated decisions ... the "energy crisis" (~1973-74) spurred the retirement of most first-generation jets and the development of more efficient high-bypass engines, and both operators and manufacturers started to pay more attention to the marginal costs of carrying around a few (or a few hundred) extra pounds of structural or systems weight over tens of thousands of flight hours
Originally Posted by
formeraa
... Nobody told DL to keep NW's older planes. And NW did refurbish the fleet interiors...
DL's business/cost/revenue/economics analysts made a compelling enough case to DL's senior management that the bottom line would benefit more from keeping the ex-NW jets than from a rapid fleet renewal