Document Information
Version 1
Created 07/02/2020 22:59
Last Updated 01/11/2023 01:59
by Matthew Woerly


There are many concepts a tower controller needs to learn in order to be efficient and proficient at his/her position. A lot of these concepts are great to know in theory, but must be put into practice in order to best control the position. As VATSIM controllers, we provide a service to the virtual flying community which is expected to be efficient and professional. For this reason, we should review one of the core and most important concepts: Same Runway Separation (SRS)

Types of Same Runway Separation

There are 3 types of same runway separation: General, Category, and Wake Turbulence, with special wake turbulence requirements for intersection departures.

General Separation - Separate a departing aircraft from a preceding departing or arriving aircraft using the same runway by ensuring that it does not begin takeoff roll until (1) the other aircraft has departed and crossed the runway end or turned to avert any conflict or (2) A preceding landing aircraft is clear of the runway. 

Category Separation - Category separation is simply separating aircraft by category alone. There are 3 categories of aircraft: Category I, Category II, and Category III

  • Category I - Small single−engine propeller-driven aircraft weighing 12,500 lbs. or less, and all helicopters. Example: C172, P28A
  • Category II - Small twin−engine propeller-driven aircraft weighing 12,500 lbs. or less. Example: PA44, C402
  • Category III - All other aircraft

Note - Categories set forth in 3-9-6 of the 7110.65Y are for SRS only and should not be confused with the J, L, and S categories as outlined in SOPs 102 and 103. The categories mentioned in these SOPs are used when determining items such as initial altitudes and departure headings, therefore should not be used interchangeably with SRS categories.

Category separation is applied by separating aircraft by a specified number of feet. This is the lateral distance, not vertical. This distance must exist by the time the second aircraft starts its takeoff roll. Separation is as follows:

  • Category I Behind Category I = 3,000 feet
  • Category I Behind Category II = 3,000 feet
  • Category II Behind Category I or II = 4,500 feet
  • Either is a Category III = 6,000 feet

Wake Turbulence Separation - Wake Turbulence Separation is separating successive departures based on wake turbulence. There are 4 aircraft groups for the purpose of wake turbulence. These categories are based on the maximum takeoff weight of the aircraft, not the actual weight.

  • Super: Airbus A380-800 (A388) and Antonov An-225 (A225)
  • Heavy: Aircraft capable of takeoff weights of 300,000 pounds or more. Example: B748, B767, B772, A330
  • Large: Aircraft that weigh greater than 41,000 pounds but less than 300,000 pounds (maximum takeoff weight). Example: B738, A321, CRJ2
  • Small: Aircraft of 41,000 pounds or less (maximum takeoff weight). Example: C172, C208, PRM1, BE9L, C550

Wake turbulence separation may be applied in two different ways: In minutes or in miles.

Because PDX and SEA are radar towers, we may use miles, which is much quicker than minutes, but it is still important to know both. There are, however, certain instances where you can only use time for wake turbulence separation (mentioned and required for intersection departures).


  • Heavy, Large, or Small behind Super = 3 minutes
  • Heavy, Large, or Small behind Heavy = 2 minutes
  • Small behind B757 = 2 minutes

Miles (preferred for PDX and SEA):

  • Small behind B757 = 4 miles
  • Heavy behind Heavy = 4 miles
  • Large or Small behind Heavy = 5 miles
  • Heavy behind Super = 6 miles
  • Large behind Super = 7 miles
  • Small behind Super = 8 miles

Note -

  1. These separation minima may not take into account separation if flight paths are projected to cross. Controllers should be proactive in assigning runways to aircraft based on their direction of flight, minimizing the need for flight paths to cross after departure.
  1. When utilizing minutes for separation, the time starts when the first aircraft begins its takeoff roll. When utilizing miles, the appropriate radar separation must exist by the time the second aircraft is airborne, meaning the distance need not exist when issuing a takeoff clearance.

Wake Turbulence Separation (Intersection Departures) - Wake Turbulence Separation for Intersection Departures is separation applied based on aircraft departing from an intersection behind another aircraft which departed at the full length of a runway.

  1. *Small aircraft weighing ≤ 12,500 lbs. behind a small aircraft weighing >12,500 lbs. = 3 minutes
  2. *Small aircraft behind a large aircraft (except B757) = 3 minutes
  3. Small aircraft behind a B757 = 3 minutes
  4. Heavy, Large, or Small behind Super - 4 minutes
  5. Heavy, Large, or Small behind Heavy - 3 minutes

*Note - These first two time intervals may be waived upon pilot request. A request for takeoff is not a waiver request; such requests must be made separately.

Note - Any of these time intervals may be waived if:

  • The intersection is 500 feet or less from the departure point of the first aircraft.
  • Successive touch-and-go or stop-and-go operations are being conducted, and the aircraft is maintaining visual separation/spacing from the departing aircraft. A wake turbulence cautionary advisory must be issued.

Note - Aircraft conducting touch-and-go and stop-and-go operations are considered to be departing from an intersection.


  1. FAA JO 7110.65Y - Chapter 3, Section 9
  2. FAA JO 7360.1E