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Does the rule say that only one IFR aircraft may land or depart at an airport at one time? I'm having trouble finding the official rule in an FAA document.

What about other VFR traffic that may be flying in the traffic pattern doing practice touch-n-goes? Would that activity be affected by the rule?

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  • $\begingroup$ Depends on city $\endgroup$
    – Squareoot
    Jun 3, 2018 at 16:52
  • $\begingroup$ At an nontowered field - when you are cleared for an approach you are the sole owner of that airport until you report landing or go missed. If there is VFR traffic in the pattern, ATC will advise you of the traffic, you are responsible for avoidance. Of course there will be little chance of pattern traffic if the ceiling is at 500 feet. $\endgroup$
    – Mike Brass
    Jun 4, 2018 at 2:42
  • $\begingroup$ Thanks Mike - does that mean that only one aircraft can be cleared for an approach for ANY runway at an airport, OR that one aircraft can have a take-off clearance for an airport on ANY runway? ATC can't issue both a take-off and a landing clearance at the same time, for the same nontowered airport, correct? $\endgroup$
    – slantalpha
    Jun 6, 2018 at 21:59
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    $\begingroup$ ATC will never issue a landing clearance nor a takeoff clearance for a non-towered airport. They will issue an approach clearance or a departure release, respectively. That is a very important distinction. $\endgroup$
    – randomhead
    Oct 28, 2022 at 16:24

2 Answers 2

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Several sections of the AIM give guidance on this. It is explicitly stated that only one aircraft at a time is given a departure clearance. It is implied that there would be no approach clearances until the departing aircraft’s position is known by ATC.

4−4−1. Clearance

a. A clearance issued by ATC is predicated on known traffic and known physical airport conditions. An ATC clearance means an authorization by ATC, for the purpose of preventing collision between known aircraft, for an aircraft to proceed under specified conditions within controlled airspace.

5−2−6. Departure Restrictions, Clearance Void Times, Hold for Release, and Release Times a. ATC may assign departure restrictions, clearance void times, hold for release, and release times, when necessary, to separate departures from other traffic or to restrict or regulate the departure flow. 1. Clearance Void Times. A pilot may receive a clearance, when operating from an airport without a control tower, which contains a provision for the clearance to be void if not airborne by a specific time. A pilot who does not depart prior to the clearance void time must advise ATC as soon as possible of their intentions. ATC will normally advise the pilot of the time allotted to notify ATC that the aircraft did not depart prior to the clearance void time. This time cannot exceed 30 minutes. Failure of an aircraft to contact ATC within 30 minutes after the clearance void time will result in the aircraft being considered overdue and search and rescue procedures initiated.

NOTE− 1. Other IFR traffic for the airport where the clearance is issued is suspended until the aircraft has contacted ATC or until 30 minutes after the clearance void time or 30 minutes after the clearance release time if no clearance void time is issued.

5−5−4. Instrument Approach

b. Controller. 1. Issues an approach clearance based on known traffic.

5−5−4. Instrument Approach a. Pilot. 1. Be aware that the controller issues clearance for approach based only on known traffic.

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  • $\begingroup$ This makes sense in IMC since two IFR flights may not be able to see each other. Buy what about in VMC, when there may be VFR flights in the area (possibly below radar) and IFR flights are getting visual approaches? $\endgroup$
    – StephenS
    Nov 26, 2018 at 15:40
  • $\begingroup$ @StephenSprunk All aircraft in VFR conditions are responsible for seeing and avoiding other traffic. That’s why airports with instrument approaches have the approach contained in Class E airspace so that you have a chance of seeing VFR traffic when you break out of the clouds. $\endgroup$
    – JScarry
    Nov 26, 2018 at 15:55
  • $\begingroup$ Logically, the point of the one-in/one-out rule is to cover cases when IFR aircraft can't see each other; if they can, though, then does the rule not apply? Or is this one of those (many) cases where logic and rules diverge? $\endgroup$
    – StephenS
    Nov 26, 2018 at 17:19
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    $\begingroup$ @StephenSprunk I don’t think logic and rules diverge, there are just different rules for IFR separation and VFR separation. Controllers are required to keep IFR traffic away from other IFR traffic. They may not even know about VFR traffic so they can’t provide separation. e.g., The ceiling can be 1500' with 3 miles visibility and in a Class E airport you can be doing touch-and-goes in the pattern. ATC may not have coverage to the ground at that airport, but if everyone is playing by the rules, the plane in the pattern is at least 500' below the clouds giving you time to see and avoid them. $\endgroup$
    – JScarry
    Nov 26, 2018 at 18:00
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The rule is found in FAA Order JO 7110.65 Air Traffic Control, which is the internal job order laying out the rules that air traffic control specialists must adhere to when providing services.

To begin with there is this subparagraph from Section 4–8, Approach Clearances, which applies equally at towered and non-towered airports:

4–8–1 Approach Clearance
f. Except when applying radar procedures, timed or visual approaches, clear an aircraft for an approach to an airport when the preceding aircraft has landed or canceled IFR flight plan.

So even at a towered airport, the default rule is that only one aircraft may be cleared for an approach at one time. The next aircraft cannot be cleared for an approach until the tower controller reports to the approach controller that Aircraft #1 has landed. Of course "radar procedures" (Section 5–9) are used at almost every towered airport in the NAS, and where those are not available there are "timed approach" procedures specified in Section 6–7.

But at non-towered airports the "one-in one-out" rule cannot be bent, not even using the "except when applying radar/non-radar/visual rules" exception from 4–8–1f. This is because of another set of rules (which also apply at both kinds of airports) concerning overdue or unreported aircraft:

10–4–1 Traffic Restrictions
IFR traffic which could be affected by an overdue or unreported aircraft must be restricted or suspended unless radar separation is used. The facility responsible must restrict or suspend IFR traffic for a period of 30 minutes following the applicable time listed in subparagraphs a through e.

10–4–3 Traffic Resumption
After the 30-minute traffic suspension period has expired, resume normal air traffic control if the operators or pilots of other aircraft concur. This concurrence must be maintained for a period of 30 minutes after the suspension period has expired.

(Note that unlike 4–8–1f, which only deals with successive arrivals, these rules concern all IFR traffic; each paragraph specifically references paragraph 4–3–4 concerning departure releases and void times.)

At a towered airport, the tower controller can observe the arriving or departing aircraft being in a correct position and operations can continue unrestricted. But at a non-towered airport, there is no-one to issue a landing clearance and observe the aircraft safely touch down; there is no-one to issue (or withhold) a takeoff clearance. Therefore every IFR aircraft which has been given authorization to arrive at or depart the airport must be considered "unreported" until proven otherwise. This is the true basis for the "one-in one-out" rule.

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  • $\begingroup$ I mean that the tower controller has the aircraft in sight and can observe that they have not crashed, nor are they in a position to affect with other IFR traffic. In other words at a towered airport the FAA, in the person of the tower controller, has a direct view of the airport and the local traffic situation; at a non-towered airport the overlying IFR controller does not have this direct view, and has to assume the worst-case scenario until informed otherwise. $\endgroup$
    – randomhead
    Oct 28, 2022 at 16:08

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