Originally Posted by
crosvs
(2) That said, if indeed it was an auto-pilot managed descent after all, I do have one horrific theory to explain the descent rate fluctuations: we saw how shifts in the center of gravity can cause even a 747 to lose control (remember the military base incident a year ago?). It's conceivable that all passengers were told to move as close as possible to the rear of the plane in an effort to slow its descent:
Figure a fully-loaded A320 with 7,835 US gallons @ 6.8 lbs / gallon = 53,278 lbs.
This was a short flight, so figure only about a third of that was used, at most(?). So maybe 18,000 lbs or so, most of which is of course over the wings. Shifting 149 people to the rear of the plane, and assuming an average weight of just 150 lbs / person means 22,000 lbs suddenly to the rear of the plane, in a desperate attempt to slow the descent. This cloud explain the varying descent rate.
I certainly don't have enough knowledge to dispute or corroborate your thoughts, but I don't see the motivation for 4U to add weight to the aircraft by carrying more fuel than would be necessary - after all, this is a subsidiary created to reduce operational cost for the LH parent.
Assuming, on most heavily loaded case, that 4U chose to fuel at their DUS hub to reduce fuel costs, they would only need enough to cover DUS-BCN-DUS - 1500 miles - plus whatever excess is needed for the increased consumption on take-off and regulatory excess.
An A320 series plane has a range of about 3,800 miles fully loaded, so - if it started with 50% capacity - a more reasonable calculation of the fuel remaining might be closer to 25%, which presumably lessens the impact of moving mass around inside the plane. Would that still be enough, in your opinion, to cause the variance in descent rate seen?