Originally Posted by
sonicbum
Nice catch, I am checking CFM/CFM LEAP data and the VMCA is 4 kts higher on the latter. Other than that, I only find a significant difference on Vref between CEO/NEO as discussed above, ie. 6 kts lower on the NEO, but that is due to the higher flap angle.
a) Vmcl
(*applies for Vmca too, but since we're discussing the approach phase Vmcl is what I had in mind already in the post above) and the Optimum Single Engine speed (green-dot) being higher for the NEO: While rated at the same 27.5k, the higher drag of the failed engine with a larger diameter could suggest the reason behind the increase of the speeds.
vilas in my book that also covers the greater GD on CFM compared to IAE. But it is the other way around for Vmca!
b)
Flap angles.
ceoCFM (sharklets or not) Full = 35°.
ceoIAE (sharklets or not) Full = 40°
neoPW (sharklets) Full = 40°
neoLEAP(sharklets) Full = 40°
Assuming higher residual thrust on all compared to CFM, the choice for a higher flap angle could arise either for handling qualities at landing (too slippery) or the need to have higher drag to assure necessary core speed to meet the go-around engine acceleration requirements. The steeper angle causes more noise and fuel burn, surely a decision taken not without a serious cause. (
Fun fact: the Full-flap limiting speed remains identical,177 kt.)
The question why on neoPW-shark is the Vref 6 kt less compared to ceoIAE-shark still stands, IMHO.