Some years ago, when there was not a high speed train between Madrid and Barcelona which links both cities centers in 2h30, IB
had around 45 flights each way during weekdays, divided in two groups:
* Puente Aéreo: Shuttle MAD
flights (example: IB1245, departing at 1245), reserved for passengers with a shuttle ticket. Shuttle tickets are valid for 365 days and you are allowed to board into the first shuttle flight with available seats when arriving at the airport, any day at any time. Before the HSR, there were 32 flights each way during weekdays.
* Normal scheduled MAD
flights: cheaper, bookable, etc. Around 12-13 flights each way. They carried a IB2xxx flight number or a IB6xxx, the last one used for connections to intercontinental flights from MAD
Since the AVE trains are in service, they have reached a 50% market share, so, in order to maximize LFs, IB
sells all their flights between MAD
as Shuttle flights and as normal scheduled and bookable flights (there are not, anymore, exclusive shuttle flights). This means that, a single flight can carry: 1) a shuttle flight number, 2) a scheduled flight number, 3) and the flight number of all the intercontinental flights which are connected to this flight from MAD
Just as an example of why things are like this right now, this is how a normal wednesday scheduled looked back in 2000 between Barcelona and Madrid:
#0535, #0655, 0700, 0715, 0730, 0745, 0800, 0815, 0830, 0900, *0930, #0955, 1000, #1020, 1100, *1200, 1300, 1400, #1440, 1500, 1515, 1530, #1540, 1600, *1630, #1635, 1700, 1730, #1755, 1800, 1830, #1855, 1900, 1915, 1930, 2000, 2030, #2035, 2100, *2130, #2135, #2140, 2200, *2215, 2245
No mark = Shuttle flight; # = Scheduled flight; * = Combined scheduled annd shuttle flight.