Is it necessary to take permission from ATC while crossing runway?

At an aerodrome with an operating air traffic control tower, never enter a runway without specific authorization. When in doubt, contact ATC.

Under which situation can you deviate from an ATC clearance?

§ 91.123 Compliance with ATC clearances and instructions. (a) When an ATC clearance has been obtained, no pilot in command may deviate from that clearance unless an amended clearance is obtained, an emergency exists, or the deviation is in response to a traffic alert and collision avoidance system resolution advisory.

Which one gets a priority at the airport runway a landing aircraft or a departing aircraft and why?

An aircraft landing or in the final stages of an approach to land shall normally have priority over an aircraft intending to depart from the same or an intersecting runway.

How does ATC decide which approach for each gate?

In practice, though, ATC runs major airports so that flights arriving through each arrival gate will usuallyget the same approach, and ATC will tell pilots to “expect” that approach. For instance, arriving to DFW through the NE or SE gates will usually get you a 17C/35C or 17L/35R approach, and the NW or SW gates a 18L/36R or 13R.

When does an aircraft not have to cross the runway end?

If you can determine distances by reference to suitable landmarks and the other aircraft is airborne, it need not have crossed the runway end if the following minimum distance from the landing threshold exists: Category I aircraft landing behind Category I or II- 3,000 feet .

When to assign initial heading to a runway before takeoff?

Do not, however, assign these routes solely to provide for possible radar or communication failure. Before departure, assign the initial heading to be flown if a departing aircraft is to be vectored immediately after takeoff. FLY RUNWAY HEADING.

What is the distance between successive departures from the same runway?

Between successive departures from the same runway- 1 mile if courses diverge by 10 degrees or more immediately after departure. (See FIG 5-8-1 .) This procedure does not apply when wake turbulence separation is required.