New Aircraft Orders Pushed Back

[Karl]

When an airline orders new aircraft, a delivery date is given.

Often, when an airline views the delivery schedule, one discovers that sometimes the delivery date is moved up.  OK, I understand that, among other things, an airline goes out of business, or it cancels and order.  In this case delivery dates might be moved up to fill now empty slots.

However, sometimes, one finds that a "confirmed" delivery date is moved back!  Why does this happen?

[Sami]

The production rate might slow down, or a new model is introduced (<-- this usually shouldn't affect much), or similar.

The actual delivery date is "locked" a few months prior delivery, and upon then it is an estimate. This is noted at the ordering page: "Please remember that the delivery times are approximate and can move if the production rate increases or if other orders are canceled. The delivery time is confirmed 6 months prior delivery."

[Karl]

i understand the warning and that the date is not set until 6 months prior to delivery.

My question, however, is why does the program apparently give priority to another airline's order? 
If my order was placed first, why does my order get delayed?  Is it because the new order is bigger or more valuable?

[Sami]

No, there no such mechanism to give any priority to big orders or anything similar.

The system does however try, in some cases & if possible, to leave at least some gaps small for new orders so that the first deliveries of new orders wouldn't be many-many years away. But of course if the line is really glogged up, this does not happen either.

And in the big picture when looking at the whole line and full orders, the one who orders first gets his order delivered first.