Grandfather rights describes a situation in the aviation industry, wherein an airline's historical dominance at an airport has become institutionalised in the rules governing that airport. The classic example is the contentious issue of 'slots' - the slices of time allocated to each airline for its planes to use the runways for take-off or landing operations.

Prior to the massive expansion of international air travel, slots were allocated to airlines by airport administrators. Latterly, they came to be seen as attractive key assets for airlines seeking control of their home airports. As a result, the buying and selling of slots by airlines to their rivals is now commonplace.

There are two criticisms of this practice. The first is that the airlines don't own these slots: the airport operator should manage the allocation of these slots, perhaps by open auction. The second is that airlines are accused of being selective in who they allow to buy slots from them, to prevent competitors gaining access to useful slots.

Forcing airlines to relinquish slots (especially those at convenient times of day) has recently become a condition of merger and alliance activities. When British Airways sought a closer relationship with American Airlines in 2002, the regulators' requirement that they give up 224 slots at Heathrow Airport proved too high a price for the airlines.