Controller's Guide to Instrument Approaches (Advanced Topics)
By Eric Stearns (ES)

Advanced Topics: In an attempt to simplify the main article a bit, we have reserved some topics for discussion here. This article presumes that you have read the first article. More on the 300' per mile rule: We've extensively used this rule throughout the article. It's not written in any official publications, so it's really more of a rule-of-thumb. It's a fairly easy way to estimate if the aircraft will be at an appropriate altitude for any instrument approach, without turning it into a trigonometry equation. The 300' per mile rule is conservative, however. Most ILS approaches have a glideslope angle of 3°. The 300' per mile rule works out to an angle of a little over 2.8°. So for the standard 3° ILS approach, 300' per mile works just about perfect because it will result in the aircraft being slightly below the glideslope. In ZLA, there are no ILS approaches with a glideslope angle less than 3°; but there are approaches with much steeper glideslopes; the POC ILS 26L has a glideslope angle of 3.76° (about 400' per mile), and the VNY ILS 16R has a glideslope angle of 3.9°. Some non-precision approaches have angles provided for pilot information between the FAF and the runway. If you look at the SAN LOC 27 approach chart above, you'll see an angle of 3.55°, which is about 375' per mile. The point of this section is to reinforce that the 300' per mile rule is not a strict rule that is never to be broken. It is a guideline that will work for any instrument approach. If you want to calculate the specifics for a specific approach, that is perfectly acceptable. Holding (.65 4-6 / AIM 5-3-7): Even though they are not usually a part of an approach, an approach controller needs to be aware of how to hold aircraft. We'll cover a few options. One way to "hold" an aircraft is to issue it delay vectors. This is very common in the RW for short term "holding." Just issue headings to the aircraft which keep it in your airspace and above the MVAs until you can allow it to continue on an approach or enter the next sector's airspace. If a subsequent controller doesn't accept a handoff, this is almost always the best way to keep it out of his airspace. For longer term holding, it's usually best to issue formal holding instructions. The pilot should be given the holding clearance at least five minutes before he'll reach the holding fix (4-6-1-c-4). Holding is described in section 4-6 in a way that does not tie everything together all that well. A holding clearance does a few things; first, it revises the clearance limit by stating, "cleared to xxx..."; next, it issues instructions on where and how to hold, specifying a direction from the fix and a radial or bearing to hold on; it specifies a direction of turn in the holding pattern (this can be omitted if a right turn is desired as this is standard); finally it gives an expect further clearance (EFC) time. For example, if you wanted an aircraft to hold NW of SYMON on the SADDE6 arrival to LAX: "N123SX, cleared to SYMON intersection, hold northwest on the Fillmore one four eight radial, left turns, expect further clearance at two one one five, time now two one zero two." If a holding pattern is published on a chart, you may instruct a pilot to hold "as published" and omit the radial and direction of the turn. This is very common in the RW, and some vatsim pilots will be able to properly comply, but they need to have the chart available to them to know the details of the hold. Just like any other time, you must ensure that the aircraft will remain within your airspace and keep a 1.5 mile buffer from your boundaries with other controllers' airspace. When you're ready for the aircraft to exit holding, you must issue another clearance so that you amend the clearance limit to the destination airport (or another fix). Phraseology in this case will depend on the circumstance...here are a few possibilities. If the previously issued routing is still valid use phraseology similar to: "N123SX, cleared to Los Angeles airport, via last routing cleared, descend and maintain one zero thousand." If new routing is required, include it in the clearance (or even if they were already issued the SADDE 6 arrival, this would still be acceptable): "N123SX, cleared to Los Angeles airport, via the SADDE 6 arrival." If an aircraft is diverting to another airport, just issue a clearance like you would to any airborne aircraft: "N123SX, cleared to Santa Barbara airport, via direct Ventura, Ventura two eight two radial, KWANG, direct, descend and maintain six thousand." Simultaneous ILS approaches at LAX (.65 5-9-7 / AIM 5-4-15): For the most part, IFR aircraft must be separated by 3 miles laterally or 1000 feet vertically. There are a few exceptions to this requirement. One exception is for simultaneous ILS approaches to parallel runways separated by at least 4300 feet. The requirements for these approaches is detailed in section 5-9-7, but for our purposes we simplify them in LAX_APP SOP section 5-h. The key thing to remember is that aircraft must be provided standard IFR separation until they reach the appropriate capture box (described by the SOP). At LAX we can use simultaneous approaches between 24L/R and 25L/R; so you could have one aircraft on the ILS 24L and another on the ILS 25R; however, simultaneous approaches may not be used between two immediately adjacent runways. For example, you could not allow them between aircraft on the ILS 24R and ILS 24L since those runways are separated by much less than 4300'. Simultaneous visual approaches at LAX and other airports (.65 7-4-4): For an airport like LAX, with parallel runways separated by more than 4300', you can also use visual approaches to lessen your workload. An aircraft can be cleared for a visual approach to runway 24R or 24L with an aircraft adjacent to it on an instrument or visual approach to 25L or 25R. These are easier because you don't need to maintain the separation required for simultaneous ILS approaches. Once an aircraft has been cleared for a visual approach, it does not need any separation from aircraft on an adjacent approach that is at least 4300' away. For example, if you have an aircraft inbound on the ILS 25L and a second aircraft on downwind for 24R, once the pilot reports the airport in sight, you may clear him for a visual approach to 24R, and no longer need to provide separation between the two aircraft. Neither pilot has to report the other in sight in this case. If these same aircraft were vectored for ILS approaches, they'd have to be provided standard IFR separation until they were both established on their localizer and inside the capture boxes. The use of simultaneous visual approaches gives much greater flexibility. See section 7-4-4-c-3 for more information and also LAX_APP SOP 5-c-5. Simultaneous visual approaches may also be used with converging runways as long as the flight paths to those runways do not intersect (see 7-4-4-c-4). For example, at LAS, aircraft may be cleared for visual approaches to runways 25L and 19R (it is also permissible to have one aircraft on an instrument approach and the other on a visual approach) and may both land simultaneously, even though they will be a little over 2 miles apart at the thresholds. In this case, neither pilot has to report the other in sight. However, this rule may not be used for aircraft approaching 1L and 7R since the flight paths intersect at the 1L threshold. When applying this rule, you should also consider runway separation if using intersecting runways. At LAS, this wouldn't be a problem between 25L and 19R since they don't intersect. If you used this rule to allow simultaneous visual approaches between runways 8 and 15 at BUR, you might create a problem if both aircraft were trying to land at the same time (using Land and Hold Short Operations might help, but there's not a lot of runway available at BUR). You may also use simultaneous visual approaches to any two parallel runways as long as the trailing aircraft has the leading aircraft in sight and is able to maintain visual separation (7-4-4-c-1). In this case, the controller must maintain standard IFR separation, until the pilot accepts visual separation. You must also consider relative speeds in this case. You may not permit a 757 or heavy aircraft to overtake any other aircraft on final; also, you may not permit a large aircraft to overtake a small aircraft (these two provisions only apply to this paragraph, not the previous two paragraphs). If you follow these rules, you may permit simultaneous visual approaches to closely spaced parallel runways (it is also permissible to have one aircraft on an instrument approach and the other on a visual approach), like 24R and 24L at LAX, 26L and 26R at ONT, 25L and 25R at LAS, etc. The key requirement here is that at least one pilot must agree to maintain visual separation from the other prior to the aircraft losing standard IFR separation. Visual Separation (.65 7-2 / AIM 4-4-13 & 5-5-12): Visual separation is a great tool that can improve efficiency. A mistake many controllers make is relying upon visual separation before they are certain it will exist. For example, if a pilot of one IFR aircraft sees another and accepts visual separation, then no ATC separation is required. However, that doesn't mean that two aircraft should be allowed to converge at 4000' with the controller counting on visual separation before they get closer than 3 miles. Always issue instructions so that standard IFR separation will exist between aircraft; if one pilot accepts visual separation, then consider issuing instructions that allow less than standard IFR separation. Also remember that visual separation may only be used below 18,000'. The .65 also allows tower controllers to provide visual separation between IFR aircraft. In this case the tower controller must have both aircraft in sight and be confident he'll keep both in sight until visual separation is no longer required. This is how RW LAX_TWR permits an aircraft to depart off 24L while another lands on 24R; he's providing visual separation between the two aircraft. "Stringing" visual approaches together (.65 7-4-3-c): Normally, you must provide appropriate spacing between aircraft approaching an airport even on visual approaches. However, if an aircraft reports another aircraft in sight which he will follow, he may be instructed to follow that aircraft and cleared for a visual approach (remember that if a pilot reports the preceding aircraft in sight, he does not have to report the airport in sight for a visual approach). In this case, the pilot is expected to take appropriate steps to sequence himself with that aircraft. You may use this to set up a "string" of aircraft, each knowing who he's supposed to follow, all cleared for a visual approach. Essentially, each pilot is maintaining visual separation from the one he is following. If an aircraft will follow a heavy or 757, then you must inform them of the type aircraft they are following; however, you are not required to provide any wake turbulence separation; that is up to the pilot. Turbine aircraft must normally remain in class B airspace (.65 7-9-3-a / AIM 3-2-3 / FAR 91.131(a)(2)): When large (defined in .65 Appendix A) turbine aircraft (jet or turboprop) depart or arrive at the primary class B airport, they should be routed and assigned altitudes such that they do not operate below the floor of the class B airspace (7-9-3-a). The lateral and vertical limits of each class B airspace area are available in the sector file (see the sector file documentation for details). Once these aircraft enter the class B airspace, they should remain in it; if you need to vector an aircraft out of the class B and back in, inform it when entering and departing the class B airspace. Note that this section only applies to operations to and from the primary class B airport (in ZLA we have five primary class B airports, LAX, SAN, LAS, NKX, and LSV). Operations from satellite airports need not comply with these restrictions; for example, an aircraft arriving or departing SMO may be vectored inside or outside the class B airspace at the controller's discretion even though it will operate below the LAX class B airspace. Keep in mind that aircraft operating below the class B airspace are restricted to 200 knots. Cruise clearance (.65 4-5-7-a / AIM 4-4-3-d-3 / Pilot Controller Glossary): This is a little used and little understood clearance that can help when a controller's workload is high. A cruise clearance is effectively an approach clearance and you should issue it at the same time you’d normally issue an approach clearance. It authorizes the pilot to fly the instrument approach of his choice and also authorizes a visual approach at an airport with or without an IAP. It gives the pilot a great deal of flexibility and, because of this, requires the controller to be able to protect a large amount of airspace. It'll probably never be useful at LAX, but if you're clobbered with arrivals at LAX and you have one aircraft inbound to CRQ, it's a way to reduce your workload. We'll look at two examples, one to CRQ (an airport with an IAP) and another to BNG, which has no published IAP. At an airport with an IAP, the rules for issuing a cruise clearance are the same as they are for an IAP clearance under section 4-8. If the pilot is on a route with a published minimum altitude, you can just say “cruise 5000.” If they are not on a route with a published minimum altitude (i.e. direct to a fix), then a crossing altitude is needed. Assuming XYZ is an initial approach fix, the clearance could be “cross XYZ at/above 5000, cruise 6000.” So, let’s assume you have an aircraft inbound to CRQ at 9000 from the NW which has been cleared direct OCN. Say you’re busy working numerous aircraft elsewhere and don't want to worry about the CRQ arrival. You could just say, “cross OCN at/above 3000, cruise 9000.” The pilot could descend at his discretion and execute the ILS, RNAV, or VOR approach; if the pilot gets the airport in sight he could also choose to fly a visual approach. Remember that this clearance gives the pilot a great deal of leeway, so make sure that he won’t be a factor for other aircraft you’re working. The cruise clearance is very similar to “cleared approach.” Using the above example, you could say “cross OCN at/above 3000, cleared approach.” The difference is that “cleared approach” requires that an IAP be flown and doesn’t permit a visual approach. So if the pilot wanted a visual approach in this case he’d have to call you back and request a visual approach clearance. BNG can be a challenging airport because of the MVAs and MEAs in the area (it's also challenging because it's right on the border of ONT_APP and PSP_APP). The MVA above the airport is 10,000'; it is possible to get an aircraft overhead at 9500' if he's established on V388. Ideally we'd like to let the pilot start down as soon as he desires and the cruise clearance allows him to do that at his discretion. At an airport like BNG, since no IAP is available, no crossing altitude is needed for the cruise clearance because of this portion of .65 4-5-7: "When issuing a cruise clearance to an airport which does not have a published instrument approach, a cruise clearance without a crossing restriction may be issued." Keep in mind that the altitude you issue in the cruise clearance must comply with the applicable MVA or MEA. So, let’s assume that the aircraft is assigned 11,000’ established on V388. All you have to say is “cruise 11,000.” This authorizes the pilot to immediately descend to 9500’ since that’s the MEA of the airway beyond ACINS. After that, it’s totally up to the pilot to determine the minimum IFR altitude (MIA) and he can descend at his discretion based on his determination of that MIA. Note that, with a cruise clearance, the controller has no role in the determination of the MIA, it’s totally up to the pilot. Since the cruise clearance acts as an approach clearance, it wouldn’t be necessary to issue a visual approach clearance. Keep in mind, with a cruise clearance the pilot can climb back to the altitude in the cruise clearance at any time (unless he verbally reports leaving an altitude). It’s really pretty straight-forward and the responsibility rests with the pilot to execute the descent. If you didn’t have the option of the cruise clearance, the lowest you could get the pilot is the 9500’ MEA of the airway and hope he could see the airport for a visual approach. Contact Approach (.65 7-4-6 / AIM 5-4-24 & 5-5-3): Contact approaches are rarely used, but a controller needs to know about them. A contact approach is similar to a visual approach in that the pilot will take responsibility for his routing and terrain separation to the airport. There are three main requirements to issue a contact approach clearance; first, it must be requested by the pilot, never solicited by the controller; second, the destination airport's visibility must be at least one mile; finally, the airport must have an operational instrument approach procedure. Like any other time, you must provide standard IFR separation between other IFR aircraft, as well as any VFR or special VFR aircraft. From the controllers standpoint the contact approach is very simple. If a pilot requests a contact approach and the operation will meet the three criteria above, you may clear him for the approach using phraseology like "cleared contact approach to Santa Maria airport." The pilot does not need to report the airport in sight; his request is an indication that he can safely complete the approach to the airport based on his observations. Like always, your main concern is ensuring he is separated from other aircraft as appropriate. Although a contact approach may be requested and approved in any weather condition (so long as the visibility is 1 mile or more), the time a contact approach is most valuable is when weather conditions do not permit a visual approach (ceiling < 1000' or visibility < 3 miles). In this case a pilot can request a contact approach and proceed to land at his discretion. Keep in mind that a contact approach allows the pilot complete discretion over his route and altitude; always make sure you can reserve a large block of airspace for a contact approach operation. Center controllers working approaches: There are many differences between center controller rules and the rules under which approach controllers operate. One difference for a center controller is that, in order to vector to the final approach course, he must have the centerline of the approach depicted on his display (5-9-1-d). There are numerous other differences; on Vatsim we compromise in ways that are unrealistic. For example, a center controller works LAX_APP and LAS_APP, which operate continuously in the real world. In order to operate these airports efficiently, center controllers must use at least some approach rules. ZLA has no written policy on this subject, so I normally use Approach rules in approach airspace and center rules elsewhere. Multiple IFR aircraft approaching one airport: The rules for handling multiple IFR arrivals vary based on the type of radar services available at an airport and whether or not it is controlled. At class B and C airports, radar service is available to the surface and the control tower will either be worked by a dedicated controller or by the overlying approach controller. In those cases, aircraft may be spaced as tightly as 2.5 miles on approach to a runway and several aircraft may be cleared for an approach to that airport simultaneously. Each controller the pilot communicates with will be able to provide radar separation. At class D, E, or G airports, continuous radar service is not available because either the tower (at class D airports) is not able to provide radar separation or the pilots will be issued a change to the advisory frequency (at class E or G airports). In these latter cases, separation can be more challenging. Normally at class D/E/G airports we use a "one in/one out" rule. This means that only one aircraft may be cleared for an approach or cleared to depart that airport under IFR. There are a couple of ways to work around this rule. The easiest is to have one pilot maintain visual separation from the other. With that you may have two aircraft arriving or departing IFR (or one arriving and one departing). It's very difficult to have three aircraft operating simultaneously since each individual aircraft must be visually separated from the other two. Also, a tower controller may provide visual separation between IFR aircraft at his discretion. For a busy class D airport, you might also use timed approaches. Timed approaches are used extensively in the real world to permit a steady stream of IFR arrivals, even in poor weather. These aren't typically used on vatsim (but for an event involving a class D airport, their use should be considered). Timed approaches are covered in 7110.65 6-7; they require an operating tower, certain weather minimums, and that an instrument approach be utilized (visual approaches may not be used with timed approaches, unless other approved separation is used). 7110.65 6-7 talks at great length about using time between arrivals to ensure separation in a non-radar environment (hence the origin of the term "timed approaches"); in the real world there are places where aircraft hold outside radar coverage and thus ATC still uses timing for separating aircraft on the approach. On VATSIM, we always operate in a radar environment and therefore can disregard all mention of timing and just use the minimum distance between aircraft (5 or 6 miles) over the FAF/OM. Between similar performing aircraft, the 5 miles would be adequate; if a fast corporate jet followed a Cessna 172, that distance would need to be increased substantially (just as it would in a radar environment). Keep in mind that it's theoretically possible that both aircraft could end up flying the missed approach procedure as well. The spacing over the FAF/OM should consider that possibility at least to the point where diverging courses could be established in the radar environment. Timed approaches may only be used at controlled airports as the tower ensures separation between arrivals and coordination of missed approaches and IFR cancellation. Arrivals at Uncontrolled Airports: Arrivals at uncontrolled airports aren't much different than arrivals at controlled airports. We talked about the fact that runways aren't assigned and circling instructions aren't issued already. Another issue is that there is no tower to keep track of IFR cancellations, so pilots must advise us when they cancel IFR. Also, they must be permitted to communicate with other aircraft at their destination on the appropriate frequency. Section 4-8-8 prescribes an exact phraseology for that. When you no longer require communication with an arrival, issue this instruction: "N123SX, change to advisory frequency approved." A pilot is required to report his cancellation of IFR or a missed approach, but sometimes it's helpful to include a reminder to "report canceling IFR" or "report missed approach." Neither of these is required however. Approach Minimums: Approach minimums are determined by the pilot; the controller has no role in determining whether or not a pilot can land out of an approach or can even commence an approach (other than ensuring the pilot has the latest weather information). In the RW, minimums required for an approach will vary between aircraft depending on aircraft equipment and pilot experience. In low visibility situations, just like any other time, the controller should issue the latest weather and either ask the pilot to "say approach request," or inform him what approach to expect. If the pilot is unable to fly an approach he is required to inform the controller. At some airports there are significant differences between minimums on the instrument approaches published for that airport. In some cases the SOP will specify runway configurations based on ceiling and visibility (like at SAN). ZLA has two airports with Category II and III ILS approaches, LAX and ONT. These approaches allow landing with much lower visibilities. There are significant differences for pilots flying these approaches, but for controllers the phraseology is exactly the same. In the approach clearance you don't add anything extra; it should still be "cleared ILS runway 25L approach" even for Category II or III approaches. The controller should be aware of the minimums published for approaches in his airspace. In some cases it will be advantageous to configure airports a certain way so that pilots can fly approaches with appropriate minimums. That said, the pilot determines whether or not he can fly a particular approach.

Eric Stearns is a staff member with ZLA, as a Certified Instructor and the Facility Engineer.