MD83FO
And I have a question for the guys flying airplanes with greater sweepback (777)
Whats the cruising Mack number at cost index zero?
The otherday, a flight to BKK (B777-300ER) from home, CI 28, Mach varied .830/840, yet CI 0 showed minus 25kg for the flight and PLUS 1 minute??? ( a loss of 25kg's, fact on Operational Flight Plan). You can see the loss for a FL below optimul, and obviously FL above is not available as you are too heavy. See the difference weight does by increasing by 1000kg or the savings by decreasing, and at the bottom you can see the fact that Cost Index 0 will cost you 25kg's.
Fuel savings accumulate over time in flight from cutting corners, to getting your correct levels, however, they can be ruined rather quickly with early descents and slow speeds far out, speed 180 for example at 40 track miles run kills what was saved.
The difference in a change of runway from straight in the opposite runway via a downwind is an easy 1000kg.
We cater ahead on a forecast and carry that extra 3% contingency, however, it can be gone in the first couple miles with an incorrect level, extra track miles for departure. There is no guarantee that it will all be there at destination, but we try.
The speed range at altitude
sometimes does not allow M.76 in B777, it is below minimum speed and we try maintain minimum speed plus 15 kts as per the book, but no body wants to fly a lower limit. As altitude is decreased, the available speed range thus increases vastly, but so does extra fuel flow. All this is dependent on may factors, specifically weight at the time of the request.
