by Eric Stearns
There are times when it is necessary for ATC to delay the progress of a flight. There can be a number of reasons, but normally holding is caused by too much traffic trying to do the same thing (usually trying enter a busy approach controller's airspace). Pilots can also request to hold. For example, if the destination airport is reporting weather below minimums and the pilot does not want to attempt an approach, he could request to hold until the weather improves. Another common time to hold, is as part of a missed approach procedure. Most instrument approaches specify a hold at the end of the missed approach procedure. When a pilot is cleared for an instrument approach, he is also automatically cleared for the missed approach procedure.
When a controller needs to delay an aircraft he has two options. The first is to delay aircraft by issuing a revised, longer route or by issuing headings which create the needed spacing. This works well for a controller who only needs to slightly delay an aircraft, or a controller who doesn't have very much traffic. From the pilot's perspective, these are very straightforward, and require no additional discussion above what is already written elsewhere in the PRC.
When a controller is busy or long-term holding is needed, pilots should expect to receive holding instructions. When receiving holding instructions, pilots are expected to fly within certain protected airspace. ATC will protect the holding airspace from other traffic; also, remaining within the protected airspace assures terrain separation. Holding instructions are issued as a revised IFR clearance, and the pilot should fly a standard holding pattern to assure that he remains within the protected airspace. This is a graphic depiction of a holding pattern and some of its terms, adapted from the U.S. Aeronautical Information Manual:
Once established in the hold, on the inbound leg the pilot tracks the appropriate VOR radial, NDB bearing, or RNAV course. Upon reaching the holding fix, the pilot turns in the appropriate direction to the outbound heading. Except for airplanes with area navigation systems (normally either FMS or GPS), positive course guidance is not available on the outbound leg; so the pilot must choose a heading to fly. In no wind situations, the appropriate heading would be 180 edegrees off the holding course. Normally there will be some crosswind component, and the outbound heading should correct for wind so that the aircraft's course does not converge on the radial/course defining the inbound leg. There are various techniques for accomplishing this wind correction which are discussed elsewhere. In a timed holding pattern, the pilot starts timing when abeam the holding fix (as depicted in the diagram above), and the pilot attempts to time the outbound leg so that the inbound leg is the appropriate time (discussed later in this article). FMS equipped aircraft, and to a lesser degree any RNAV equipped aircraft, can fly extremely precise holding patterns since they can calculate the wind, turn rate and radius, and position relative to the inbound course. Pilots flying non-RNAV aircraft will find holding more challenging. It is as much an artform as anything in aviation. Every hold is different, and strong winds can make them especially challenging.
The phraseology for the holding clearance should be similar around the world; in the U.S., the phraseology is very standard and consists of a clearance limit, direction to hold from the fix, the radial or bearing on which to hold, leg lengths or timing to be used in the pattern (if non-standard), direction of turn (if non-standard), and a time to expect further clearance toward the pilot's destination. Let's look at each of these separately:
- Clearance Limit ? This is the endpoint of the pilot's IFR clearance. Almost always, this clearance limit is the pilot's destination. Holding clearances should revise the clearance limit to the fix at which holding will take place.
- Direction to hold from the fix ? This should be one of eight cardinal directions that indicate which way the pilot should hold. The direction will be indicate which direction the pilot will hold from the fix. For example, if the pilot is told to hold east of a fix, then the holding pattern itself is east of the fix.
- Radial or Bearing ? This will precisely define the course on which the pilot will hold. It is normally expressed as a VOR radial or NDB bearing. It can also be an airway or other type of route. This course will be tracked on the inbound leg of the holding pattern.
- Time or distance ? To keep the holding aircraft within a predictable area, the pilot is required to use either time or distance to define where he should begin turning back toward the holding fix. In the U.S., timing is standard. In a standard hold, the pilot should attempt to make his inbound turn so that his inbound leg to the holding fix is 1 minute (at/below 14,000') or 1? minutes (above 14,000'). Controllers may also assign, and pilots may request, a distance to be used in holding. If a distance is specified, begin your turn back toward the holding fix when you reach the distance specified from the holding fix. For example, if 10 mile legs are specified, begin your turn to the inbound leg when you are 10 miles from the holding fix.
- Direction of Turn ? Once established in a holding pattern a pilot will always turn the same direction. In the U.S., the standard direction is turns to the right. So, if the controller omits a turn direction, right turns are implied. The holding pattern depicted in the diagram above uses right turns.
- Expect Further Clearance (EFC) Time ? For planning purposes and in case of lost communications, the controller should issue an EFC time. This number just gives the pilot an idea of how long he might hold. In the event of lost communications, the pilot should depart the holding fix at the EFC time, and proceed to his destination via the last routing cleared.
Entering a Holding Pattern
The discussion to this point has presumed that you are established in the holding pattern. There are some basic techniques to entering holding patterns. The main objective is to remain within the protected airspace to assure traffic and terrain separation. FMS systems and some GPS systems will automatically calculate an appropriate track to fly through the hold entry. However, pilots should be prepared to fly the entry manually. The U.S. Aeronautical Information Manual includes a diagram suggesting three entries, depending on the direction from which you'll arrive at the holding fix:
(a) Parallel Entry ? If you will approach the holding pattern from area ?(a)? above, a parallel entry is suggested. To execute a parallel entry, upon crossing the holding fix turn to a heading that parallels the holding course and time for one minute. At the end of the minute, begin a turn toward the holding pattern to a heading that will intercept the holding course prior to the holding fix. Once you arrive at the holding fix, begin a turn in the appropriate direction to the outbound leg.
(b) Teardrop Entry ? If you will approach the holding pattern from area ?(b)? above, a teardrop entry is suggested. To execute a teardrop entry, upon crossing the holding fix, turn to a heading that is 30 degrees offset from the outbound leg heading and time for one minute. At the end of the minute, begin a turn toward the holding course and intercept it. At the holding fix, begin a turn in the appropriate direction to the outbound leg.
(c) Direct Entry ? If you will approach from area ?(c)? above, a direct entry is suggested. This is the easiest entry. When you arrive at the holding fix, begin a turn in the appropriate direction to the outbound leg.
In each case above, after turning to the outbound leg, start timing abeam the holding fix for the appropriate interval. At the end of that time, begin a turn to intercept the holding course back to the holding fix. As you make each circuit you can fine tune the time you fly the outbound leg so that the inbound leg lasts one or one-and-a-half minute(s) as appropriate. Also, modify the heading you use on the outbound leg so that you don't overshoot or undershoot the turn to intercept. Ideally, as you finish the turn to the inbound leg, you should roll out exactly on course.
Maximum Speeds while Holding
In order to keep aircraft in a reasonable area while holding, maximum indicated airspeeds are prescribed for holding aircraft depending on altitude:
- Up to 6000' - 200 knots
- 6001' to 14000' - 230 knots
- above 14000' - 265 knots
Holding patterns can be limited to 210 knots. Here's an example of a holding pattern limited to 210 knots taken from the Dylin Three arrival to Newark:
Exiting the Hold
When the controller is ready for you to exit the hold, you will be issued a clearance to your destination (or rarely to the next holding fix). In this case, you may turn toward the holding fix at your discretion (i.e. you do not need to fly a complete outbound leg). At the holding fix, begin flying the route specified in your clearance. Instead of issuing a pilot nav route to fly, the controller may assign a heading to fly for vectors to some point.
Holding at a VOR
Here's an example of a published hold at a VOR taken from the Janesville Four arrival to Chicago O'Hare airport (in each example, the diagrams emphasize the hold for clarity):
In this case, more than likely you would arrive at JVL already established on the STAR course. The holding clearance might sound something like, "cleared to JVL VOR, hold west on the 289 radial, expect further clearance at 2200Z" (note that a controller could also assign holding 'as published' if he knew that the pilot had the chart). If you were flying with just a VOR receiver, you would track the 289 radial inbound (remember that you would select 109? on your VOR head in this case) until you reached the JVL VOR. Upon crossing the VOR, turn right outbound to a heading of around 110 (correct this heading for wind drift if you can); once you're abeam the VOR (indicated by the to/from indicator changing from 'from' to 'to') start timing for one minute (1.5 minutes if above 14,000'). At the end of the time, turn right back toward the VOR and reintercept the 289 radial. Ideally, you should roll out of your turn and be centered on the radial; if not, then correct your outbound heading on the next circuit to compensate. Begin timing once you roll out on the inbound leg. The inbound leg should be one minute (again, 1? minutes above 14,000'); if the time is not one minute, then adjust the time of your outbound leg the next time around to try to get the inbound leg to be one minute.
Holding at an Intersection
Here's an example of a published hold at an intersection taken from the Ramms Five arrival to Denver:
This is a very complex chart as you can tell by all the details that are deemphasized in the chart. That can be one of the challenging parts of some holding patterns ? cutting through the clutter of the chart. For this holding pattern, DME will make the hold easier, but is not required. The holding clearance might sound something like, ?cleared to RAMMS, hold northwest on the 311 radial, expect further clearance at 2200Z.? In the holding pattern, you'll track inbound on the 311 radial (again, selecting 131 as the course on the VOR head). You'll identify RAMMS one of two ways (without an RNAV system). With DME, RAMMS is defined as 46 miles from DVV; with only VOR receiver(s), RAMMS is identified by the 256 radial from GLL. Upon crossing RAMMS, turn right outbound to a heading of around 310 (correct this heading for wind drift if you can); you can't really determine when you're abeam an intersection without RNAV, so start timing for one minute (1? minutes if above 14,000') once you roll out on your outbound heading. At the end of the time, turn right back toward RAMMS and reintercept the 311 radial. Ideally, you should roll out of your turn and be centered on the radial; if not, then correct your outbound heading on the next circuit to compensate. Begin timing once you roll out on the inbound leg. The inbound leg should be one minute (again, 1? minutes above 14,000'); if the time is not one minute, then adjust the time of your outbound leg the next time around to try to get the inbound leg to be one minute.
Missed Approach Holding Pattern
Here's an example of a missed approach holding pattern taken from the ILS 19L approach to San Francisco:
Missed approaches are covered in another article, but this one illustrates a parallel hold entry (a teardrop entry would also work in this case). The missed approach procedure instructs you to intercept the SFO 101 radial and proceed to DUMBA to hold. Upon arriving at DUMBA (defined by DME from I-GWQ, the OAK R-138, or the OSI R-036) begin timing for one minute and continue tracking the SFO R-101. After one minute make a turn to the right, so that you remain in the protected airspace. Continue turning until you are on a heading which will intercept the R-101 back inbound (30-45? intercept angle suggested). Once you arrive at DUMBA, turn left to the outbound heading; once you roll out on the outbound heading begin timing for one minute, then turn left to reintercept the SFO R-101. Ideally, you should roll out of your turn and be centered on the radial; if not, then correct your outbound heading on the next circuit to compensate. Begin timing once you roll out on the inbound leg. The inbound leg should be one minute; if the time is not one minute, then adjust the time of your outbound leg the next time around to try to get the inbound leg to be one minute.
Holding makes more sense once you practice it a few times. Set up your flight simulator first with no winds and try entering and flying the holding patterns shown above. As you feel more proficient, set a strong crosswind and try it again. You can also ask to hold when flying on the network and ask the controller to provide feedback (workload permitting) on how you flew the hold. As with any flying subject, feel free to post questions in the Vatsim Forums if something doesn't make sense.
U.S. Aeronautical Information Manual∞ (you'll have to scroll down to section 5-3-7).
FAA Instrument Procedures Handbook∞ (search the PDF document for the term "holding")
FAA Instrument Flying Handbook∞ (again, you'll need to search the PDF document for the term "holding")