So what´s this cost index thingy all about?

[DJXL]

Hi folks,

Just wondering, what´s cost index? How does it work? How does it affect the flight? And how do you come up with the number?

Seen it punched into the computer many times but never thought to ask before.

Thanks!

[crisispilot]

It defines how economically the aircraft will operate. A low cost index will be the most economic, where as a high cost index will get you there faster, but cost more in terms of fuel.

[DJXL]

Brilliant, cheers folks!

[fantum farter]

Nicked from somewhere else:
Cost Index is a measurement of the efficiency of the wing with inputs from fuel costs,winds,passenger load,etc.A cost index of 0 is right at lift/drag max ie you hover all day and dont burn much fuel.
A cost index of 999 pushes you up to Vmmo/Mmo.
Picking an average speed of M.80 and working backwards into a chart comes up with the cost indices most commonly used.

with my company we use 45 for a cruise around M.79

[wysiwyg]

fantum - and then rather daftly on the bigger model we still use 45 and then force the cruise mach up by manually inserting a speed. Doh!

regards
wizzy

[Fright Level]

Trouble with that Wizz is that you cruise faster but at TOD the speed comes right back. If you manually enter a speed for CRZ, then also enter a descent speed or adjust the CI so the DES speed matches the cruise speed so you don't slow down then come down, that annoys the ATC guys.