The new plan, being announced on Sunday, goes further by letting carriers hand back unused slots temporarily, while having the right to still use them the following year.
It is intended to allow them to axe flights at least two weeks in advance – anticipating potential problems rather than reacting to them.
The government believes this would reduce the risk of last-minute cancellations.
The plans will give “more flexibility to airlines to plan their schedules”, said Alexander.
“The last thing I want is any passenger turning up at the departure gate to receive a text message saying that their flight is cancelled,” she added.
Airlines UK, which represents UK-based carriers, has welcomed the move.
Its chief executive Tim Alderslade said the plan would allow them to “avoid unnecessary flying and continue operating as efficiently as possible while protecting connectivity for passengers and trade”.
The move requires legislation, in the form of a statutory instrument, and a short consultation is taking place this week.
The government says it is also looking at ways to “increase flexibility of jet fuel supply”, including possibly allowing a US specification of fuel, known as Jet A, to be used in the UK.
Shadow transport secretary Richard Holden said the plans showed Britain was “exposed to fuel supply risks that a properly energy-secure country would not face.”
Airlines in Britain and across Europe are obliged to use a different formula, Jet A1, which has a lower freezing point.
Jet A might help reduce the risk of shortages for UK airlines, but high demand and infrastructure challenges may make this a tall order.
