Originally Posted by
tdracer
Winglets - at least winglets that do any good - change the wing loadings and require significant structural mods. A buddy of mine worked the Aviation Partners winglets that are installed on 757/767. According to him, the wing structural mods needed cost upwards of $1 million per airframe to retrofit and several weeks down time (usually performed during heavy maintenance to minimize the impact).
Winglets are not a bolt-on retrofit...
very true that....big job