Hi Ezequiel
This is a tricky word to translate into Spanish and I think you'll probably need to handle it differently in different contexts, but the basic meaning is volume or flow of passengers. It's related to the "hub and spoke" system of managing airline routes. Because point-to-point direct flights from every possible origin to every possible destination are economically unviable, because most of the aircraft would be flying with very few passengers, you have long-haul flights between hubs, major centres, and then shorter flights that connect with the hubs, like spokes of a wheel. "Feed" can be a noun meaning a flow of passengers from the spokes to the hub, or a verb meaning to provide such a flow of passengers. Here's a short study of the system called "Fares and Network 'Feed': Estimating Economies of Traffic Density in Airline Hub-and-Spoke Systems", which clarifies the meaning of "feed":

"1 By feeding all passengers through a hub, such a network generates high traffic densities on its spoke routes. This allows the airline to exploit economies of traffic density, under which cost per passenger on a non-stop route decreases as traffic on the route rises.
2 Network "feed" (the flow of passengers through the hub) thus generates efficiency gains, reducing the cost of providing airline service."
https://archive.org/stream/faresnetworkfeed91180brue/faresne...

You can therefore talk about a "feeder" airline, one operates flights on the spokes, providing passengers for the long-haul flights:

"feeder airline
Commuter carrier that brings-in (feeds) travelers from destinations not served by large carriers to hub airports for onward journey on national and international airlines."
http://www.businessdictionary.com/definition/feeder-airline....

Now, the verb "alimentar" is used for this in Spanish. In fact we had a previous question in which cranesfreak, a colleague here who is very good on transport matters, offered "alimentadora" for "feeder":
http://www.proz.com/kudoz/english_to_spanish/transport_trans...

And here's a very relevant study in Spanish, "El sistema «hub and spoke» en el transporte aéreo", which includes the following usages ("hub and spoke" is called "aporte y dispersión", though the anglicism "hub" is widely used in Spanish aviation):

"El primero de los modelos, de aporte y dispersión simple, se encuentra presente de forma directa o solapada en la inmensa mayoría de las redes de aerolíneas, se trata con ello de alimentar con varios subflujos de tráfico operados con aeronaves de capacidad medio-pequeña en vuelos de corto y medio recorrido, a un siguiente vuelo con oferta de gran capacidad, normalmente de largo recorrido, como por ejemplo los vuelos transoceánicos o intercontinentales (fig. 1)." [...]
Los puntos centrales reciben de los restantes puntos de la red una serie de vuelos en oleadas, que llegan y salen en un orden que permite que cada uno alimente a los restantes" [...]
"[...] un modelo de doble aporte y dispersión entre Madrid y Buenos Aires con aviones B-747 de 420 plazas de capacidad, con un sistema de alimentación en ambos extremos de la línea que cuenta con un grupo de vuelos domésticos de radio medio."
http://revistas.ucm.es/index.php/AGUC/article/download/AGUC9...

And the expression "vuelo de alimentación" is used:

"El director comercial y de cliente de la aerolínea, Manuel López Aguilar, en un encuentro con la prensa, explicó ayer que «es evidente que el efecto sobre la demanda de la inauguración del AVE a Valencia va a ser muy importante». Por ello es previsible que Iberia solo mantenga con Valencia los vuelos de alimentación para su red de larga y media distancia"
http://www.abc.es/20101022/comunidad-valencia/iberia-plantea...

In the contexts you've quoted I think you could use "alimentar" for "provide feed" in (1), and "vuelos de alimentación" for "feed" in (2) and (3), though it would also be possible, and might produce a better result in some cases, to use "flujo (de pasajeros)" or "volumen (de pasajeros)".