FLT86,
Same for the penalty of climb gradient on cruise with one engine inop (turbo-prop) => 1.1%.
Should I know it ?
The deduction is already taken account of by the AFM so there's no point in committing the figure to memory. Planning a route based on drift down capabilities presented in the AFM, while observing CAT.POL.A.215 ENR OEI requirements, ensures that the design incident probability of a catastrophic outcome is preserved. The incident probability would increase unacceptably if the AFM did not make the deduction.
Here is a relevant Boeing slideshow from 2002,
Operations in Mountainous Areas, for your pleasure:
http://www.smartcockpit.com/download...nous_Areas.pdf
If you're interested in the history of the 1.1 percent gradient you can find it in chapter 5 of the report developed by the 1953 ICAO Standing Committee on Performance. HathiTrust maintains an electronic copy here:
Final report of the Standing Committee on Performance. ... . - Limited View | HathiTrust Digital Library | HathiTrust Digital Library