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I am an ATC'r stationed overseas where we service two military airfields. The runways are 3 miles apart but converge. Our current regulations require aircraft from one airfield to delay in takeoff position while another aircraft is released or cleared for an approach to the other airfield, in order to protect from the missed approach point or departure route. However, our SIDS are designed to turn aircraft 45 degrees away from the other converging airport, but we are still required to wait.

We are in class G airspace with one airport 24/06 and the other, just south about 3.8 miles, on rwy 29/11. 90% of the time Rwys 24/29 are in use. The closest point of divergence, I'll have to double check for the exact distance however, the 24 departure SID is an immediate right turn off departure end, diverging at least 45 degrees from the missed approach or even departure of the southern airport in contention. Current rules require releases to be held if one or other other airports is departing aircraft however, it seems like the flight path deconflicts initially, making this unnecessary. I'll double check the distance, but our airspace isn't a factor. It's simply cutoff procedures that seem as a fail safe way of preventing an issue should the pilots heavily deviate from the SID (essentially flying rwy heading off 24) but very restrictive during departure phases.

Is there ANY way around this? Is it legal to clear both aircraft for departure with a SIDs that deconflict by 45 degrees from seperate airfields?

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    $\begingroup$ What is the airport/airspace class look like? Can you maintain required separation at the closest point of divergence? Really this will boil down to local procedures, it's unlikely that even if there is a "legal" way of doing it, your airspace operations may not allow it. $\endgroup$ – Ron Beyer Feb 17 at 20:11
  • $\begingroup$ Ron, thanks for responding. We are in class G airspace with one airport 24/06 and the other, just south about 3.8 miles, on rwy 29/11. 90% of the time Rwys 24/29 are in use. The closest point of divergence, I'll have to double check for the exact distance however, the 24 departure SID is an immediate right turn off departure end, diverging at least 45 degrees from the missed approach or even departure of the southern airport in contention. Current rules require releases to be held if one or other other airports is departing aircraft however, it seems like the flight path deconflicts initially, $\endgroup$ – Jefe Feb 17 at 21:40
  • $\begingroup$ I'm not an expert hence the comment. I'm not sure that you'll get any good answers without the SIDs on hand. ICAO specifies rules for the protected areas of instrument procedures and each type of SID has different protected area. Do the SIDs in question have overlapping protected areas? Then I guess you can't give simultaneous take offs. Alternatively are they vertically separated eg at or below 4000 vs at or above 5000 for the closest legs? Just a couple of thoughts that might help. Interesting question by the way. $\endgroup$ – Stelios Adamantidis Feb 18 at 23:08
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If this were in an FAA ARTCC's airspace, they'd handle them as one airport, because of their proximity. The protected lateral airspace for an aircraft is 4 miles either side of the course to be flown. That eliminates a lot of possibilities.

In a non-radar environment, with only 3.8 miles between the airfields, you need a reduced separation rule, such as the 13/3 DME rule (7110.65 6-2-1, a3). One and two minute rules won't work, because of the convergence. If you have a NAVAID that the departures fly over, you can use 3 miles between aircraft (faster in front), until their courses diverge. The divergenge has to be 45 degrees or more, and the NAVAID has to be within 13 DME of both airports to use the rule.

The 44 knot rule (7110.65 6-4-2) could possibly be used if you can maintain a minimum of five miles between the aircraft. Remember to account for any local speed restrictions (such as 250 knots below 10,000 feet) that may keep you from having 44 knots between your aircraft. Also, the 44 knot rule is based on filed true airspeed, not ground speed. But again, someone has to wait.

If this is a radar environment (I'm assuming you use 3 miles separation), you can release the second aircraft as soon as you get radar on the first (using radar contact within one mile of runway end) as long as you maintain 3 miles.

These rules are usable in either terminal or enroute environments. There may be more in 7110.65 chapter 3, but I don't go there, being a center controller.

If it's possible to post a plan view of the airspace, there's some CTO rated controllers on here that could give more definitive answers.

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