Can tower clear aircraft for take off with traffic still on the runway?

Question

How much separation is required after an aircraft lands before ATC can clear another aircraft to take off from the same runway? On longer runways are small aircraft allowed to commence take off roll or be cleared for take off while the preceding landing aircraft is still on the runway? I looked and was unable to find any ATC instruction requiring separation between landing and departing traffic on the same runway.

While this would be unsafe, it seems to me that I have been cleared to take off while there was still an aircraft finishing its landing roll. By the time I had lined up for take off the preceding traffic is alway clear but is this still a "legal" practice to be cleared for take off before the preceding air craft calls "clear of the active"

Answer 1

According to the ATC orders controllers can indeed clear an aircraft for takeoff 'early':

3−9−5. ANTICIPATING SEPARATION

Takeoff clearance needs [sic] not be withheld until prescribed separation exists if there is a reasonable assurance it will exist when the aircraft starts [sic] takeoff roll.

A common scenario would be clearing an aircraft that's holding off the runway to take off while the landing aircraft is still on the runway. If the controller expects that the landing aircraft will be off the runway by the time the holding one turns onto it, then it would be allowed.

Section 3-9-6 lists the conditions for allowing an aircraft to start its takeoff roll. It's too long to quote here and you can read it yourself but the two main conditions seem to be:

• The other aircraft has departed and crossed the runway end or turned to avert any conflict
• A preceding landing aircraft is clear of the runway

Answer 2

All references for this answer are in the FAA Order 7110.65.

A departure cannot start their takeoff roll before the previous arrival has cleared the runway. What most controllers will do, is use a provision for anticipated separation (3-9-5), which basically means, if someone's holding short, and you can predict when the arrival will exit, you can go ahead and issue the take-off clearance. The controller will keep an eye on things, and if it looks like it won't work, or something's changed, the pilot of the departure will be told something along the lines of: "[Callsign], cancel takeoff clearance, runway [x] line up and wait, traffic exiting downfield".

Can 2 or more aircraft be on the runway at the same time for the same type of action? Yes, in a few cases.

• Between 2 arrivals, during daylight, small single engine propeller driven aircraft, and small twin engine propeller driven aircraft weighing less than 12,500, as long as the lead aircraft is at least 3000, or 4500 feet down the runway, the next can continue and land.
• Also departures, depending on type, the as long as separation exists, 3000, 4500, or 6000 feet and airborne between departures is all that's needed under normal situations.

All the full details can be found in Chapter 3, Sections 9, 10 of the 7110.65.