What the heck are the airlines with 2million people doing.
Invest lots of time. I did some failures at start and had to countervail this by hanging at the used market 16 hours a day (and working on the other monitor).
Also be clever by choosing your aircraft, A300 and B757 are very nice in the first years, but they are weak to smaller competition.
What planes did they start out with.
1x DC-10-30 what was very stupid, because (my experience) you need at least two for earning money. This one costs me every week about 100k, but with the second one it earned me more than 1.5 million per week.
1x B737-400. The workhorse, profits were ok and after the third used 737-400 I could lease another DC-10-30.
After that you have to decide if you wait for the same aircraft or if you go for other models. My competitor had 40 aircraft more than me and thanks to the new delivery system, it's impossible to build up (fast) a big long-haul fleet, so I leased 737 next generation (new, used market), 777 (all new), 747 (new, used market) and A330 (used market, new). After you have a stable income, you can go for props if there is demand for it.
Don't care too much about fleet commonality at the start when fuel prices are low and never ever care about engine commonality.
I think there are better ways to equip your airline, but this is how I did it and you asked
How could they just expand so rapidly.
Never hord money. At the beginning spend every coin for used aircraft and if you have something about 20 Million, buy new. If you have a positive profit margin in the first years, you expand not enough.
How's my airline failing? What am I doing wrong?
See Talentz post.