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This week's topic:
IFR Flight Part 5a: Arrivals
Descent for Landing
ATC Clearance
"When Ready" Descents
Landing Information
ATIS
ATIS Acknowledgment
Transition from En Route to Arrival Phase
Clearance Required
for Transition
NAVAID for Approach
Procedure Turn
NAVAID on Route
of Flight
DME Arc
Radar Vectors
Intermediate Fixes
RNAV STARs
Unrestricted Approach
Contact and Visual Approaches
Circling Procedures
Missed Approaches
Missed Approach Point
Alternate Missed Approach
Instructions
Successive Arrivals
Advance Notice of Intent
In the on-going series dedicated to IFR flight, we have gotten our clearances, departed, and flown to destination. Now we have to descend and land. I have already covered some important aspects of this way back in April, including what altitudes are allowable for use on approach assuming no ATC or an unrestricted approach clearance. Please refer to that section in the archives, titled IFR Altitudes: Cruise and Descent. There were many items that were not covered, so I'll attempt to cover some in more detail this week.
As an aircraft approaches its destination, it follows that what goes up must go down. If the aircraft is in controlled airspace, the pilot must request descent from ATC. In VATSIM, this isn't always the case, as controllers are not always online. If a pre-descent checklist is to be completed before descending, I'd recommend its completion before the descent is requested, for a couple of reasons. First, when a pilot requests descent, a controller issuing a descent clearance will expect said pilot to commence descent promptly, not fly another 5, 10, or 50 miles before starting down. Also, a controller may be able to provide a descent clearance promptly, with the understanding that the pilot will start down right away.
Understandably, pilots would like to make a descent at an optimal point, often called "Top of Descent" by Flight Management Computers. Programming an FMC for the descent and having everything go as expected certainly does provide sense of satisfaction. For this purpose, though, a pilot would obviously prefer to have the descent enabled prior to reaching TOD so the aircraft can just do its thing. By extension, the pilot would often like have the descent clearance in hand, such that it can be started at that point. A pilot can choose to "wait it out," hoping for perfect timing and that ATC (and traffic) can permit that descent, or a pilot could initiate the request. But how to word it? As mentioned, if a pilot were to just ask for descent, ATC would expect that to begin promptly. One option is give the controller a "heads up," saying something to the effect of, "... would like to start descent in 20 miles." This gives the controller an opportunity to evaluate traffic expected to conflict at that point and offer choices: perhaps "descend now or be held up for another 20 miles beyond that point," for example.
What options does a controller have? In Canada, controllers may offer a pilot a clearance to descend, "when ready." The AIM tells us that a pilot in receipt of such a clearance may commence descent at any time that is convenient or appropriate from the pilot's perspective. Canada once used -- and the US still uses -- the term, "at pilot's discretion," which means mostly the same thing, but with an added twist: The pilot may choose to level off at an intermim altitude for a period of time, then recommence the descent to the cleared altitude when the pilot wishes. Such a pilot may not, however, return to an altitude previously vacated, regardless of interpretation. American pilot's may not understand the phraseology, "when ready," and may take it as a descent instruction, thinking it means the pilot must descend now. Even Canadian pilots will often read back a "when ready" descent clearance with the term "pilot's discretion". Some of it is old habit, some it may stem from misunderstanding.
This "when ready" phraseology serves the Canadian controller one extra purpose: Radio air time should be considered valuable by a controller. If the radio is blocked, control instructions may not be deliverable, and sometimes timing really is everything. Also, a pilot experiencing an emergency may have limited time to communicate it, and extra radio chatter can prevent such timely communication requirements. Waiting for a pilot to ask for lower means one extra, albeit short, radio call. A controller should have at least a basic understanding of when a pilot might want to begin descent, and offering a "when ready" descent clearance allows the controller to have that conversation at a time that works best from an ATC workload perspective. Getting in the habit of offering descent before it's requested yields a ATC control of their own frequency and timing.
When approaching an airport for landing, a pilot should have all the pertinent information required. ATC has a requirement to give arriving pilots Landing Information either before or shortly after descent is commenced. ATC's Manual of Air Traffic Services defines what a controller is supposed to give a pilot. This includes all information required to plan a descent and execute an approach procedure, such as (but not limited to):
"Pertinent information" includes things like Runway Visual Range (RVR) in bad weather (for runways so-equipped), pilot reports of turbulence or wind shear on final, Runway Surface Condition Reports during winter-time operations, NOTAMs regarding the airport and surroundings, and the list goes on.
ATC should not be clearing aircraft for RNAV STARs unless they possess the ability to use them. Aircraft filed "/s" for equipment, for example, will not be capable of of flying a STAR that is not built on ground-based NAVAIDs like VORs. Normally, if an aircraft is capable of an RNAV STAR, and the pilot wants to do it, this request would be made in the flight plan, in the route section.
At busier airports, giving landing information to individual aircraft can be time-consuming. Remember what I said about controlling one's workload earlier? Wouldn't it be nice to be zinged through the localizer because the controller was providing another pilot with landing information? To solve this problem, there is the well-known ATIS, or Automatic Terminal Information Service. Here, on a dedicated frequency, pilots can listen to a message containing all the information listed above. Older systems required human input: A controller would actually record the message by reading off the weather and airport conditions for playback over the ATIS frequency. Newer systems include a recording of many key words, in Canada, by a guy named Steve, and a computer reviews the weather and any other notes included by ATC at the ATIS terminal and puts the appropriate words together to make the same message. This system is controlled by the Tower at the airport. For cases where the pre-recorded words and phrases are not enough, ATC has the ability to record segments of audio to be included in the ATIS broadcast.
Each ATIS message is coded with a phonetic letter. This way, a pilot need only acknowledge receipt of the latest ATIS message by confirming receipt "Information ALPHA", or whatever letter is the current message. If ATC hears a pilot say that, it means the pilot has all the latest information -- aka ":"the numbers" -- and the controller need only issue the current altimeter setting for the destination airport. If an RNAV STAR is being flown by the pilot, the controller must issue the landing runway, and the pilot should inform the controller of the requested approach if multiple approaches to that runway are available, and it wasn't stated specifically which approach to expect on the ATIS or the pilot would prefer an approach that differs from the one advertised. Such a conversation might sound like this:
Pilot: Halifax Arrival, Citation Golf Alpha Bravo Charlie, one seven thousand for one zero thousand, Information Oscar.Transition from En Route to Approach
Somewhere along the way, a pilot must make the transition from the enroute phase of flight to the arrival, or approach, phase. There are a number of ways to do this. Remember, in each case, if flying on VATSIM and ATC is online and treating the airspace around the destination airport as controlled airspace, a pilot needs authorization in the form of a clearance to navigate via any of the methods mentioned below. A pilot needs only ask ATC for what is desired.
ATC may provide a clearance for a pilot to fly to a NAVAID or fix/waypoint associated with an Instrument Approach Procedure (IAP). At the some instrument approaches in Canada, an NDB is provided either as a Final Approach Fix (FAF), or as an approach aid. Many of these are low powered NDBs and as such, aircraft without RNAV may only be receive them within a fairly short distance, say, within 25 NM or so. Such a clearance might sound something like, "CVA116 descend to 4,000. When able proceed direct Moncton NDB". In this example, the QM NDB serves as the final approach fix for the ILS Runway 29 Approach, and a pilot can conduct an approach from this facility. Without further intervention, this would require a procedure turn -- something that is going the way of the dodo, but will be discussed anyway for completeness.
A Procedure Turn is a maneuver designed to place the aircraft on the final approach course from whatever flight path the aircraft started on when arriving over the NAVAID associated with the instrument approach procedure. Like a hold, there is more than one entry procedure permitted depending on the direction from which the aircraft is approaching the NAVAID. One thing that should be mentioned is that the report of being by the final approach fix "outbound" during a procedure turn is just that: outbound. I have been the recipient of many "outbound" reports in the real world where the pilot was over the fix and commencing the turn to go outbound when the report was made. This is not right. The AIM RAC 9.14 shows that the outbound report should be made when the aircraft is over, or abeam, the fix and heading away from the airport, not when commencing the turn to go outbound.
In some cases, the instrument approach aid to be used is actually part of the airway being flown. Take, for example, the VOR Runway 24 Approach at Moncton, NB (CYQM). The YQM VOR makes up one fix on V300, and an approach may be conducted from that facility. This would require a Procedure Turn to line the aircraft up on final.
An older method of transition that still exists at some airports that are served by DME facilities involve DME arcs. These are published from certain airways to allow pilots to intercept DME arcs and fly them from the airways to localizers (or VOR radials or NDB courses, whatever is appropriate) to make the transition to the approach.
By a similar means, sometimes an enroute fix on an airway can make up a transition to an IAP in way that a NAVAID can. While a current example eludes me, V471 was an aiway between the Moncton (YQM) and Houlton (HUL) VORs and a fix on that airway was comprised of the intersection of the airway and the localizer for the former ILS RWY 15 at Fredericton, NB. As RNAV gained more of a foothold in everything related to aviation navigation, this sort of thing has steadily fallen in prevalence in favor of more practical nav capabilities.
At airports served well with surveillance coverage, ATC may be able to provide vectors to final. This was the normal practice at airports served by Terminal Control Units across the country, and is still the most common transition in these environments in multiple-traffic situations. In some areas, the lesser-traveled airports can benefit from the more prominent presence of ATC radar over the last few decades and space-based ADS-B promises more. Aircraft may be able receive vectors to final in areas that previously had no coverage. Especially in the fringe areas, ATC workload has to permit this even if surveillance coverage does.
While the prevalence of a such a requirement has certainly diminished with the advent of RNAV-based IAPs, it is sometimes the case where ATC must delay subsequent arrivals -- a little or a lot -- and vectors can be a handy way of intervening such that holding clearances are not required. (Who likes to issue holding clearances? Who likes to fly them?)
Enter Area Navigation (RNAV): Advancement in navigation and avionics have led to new navigation systems that allow point-to-point flight without requiring an aircraft to fly courses associated with ground-based NAVAIDs. Inertial Navigation Systems (INS), and more commonly these days, GNSS. (GNSS is the initialism for "Global Navigation Satellite System", which is a catch-all term for satellite navigation. GPS is but one of these, and is the most common, though the European Gallileo and Russion GLONASS are others, and the Chinese are lauching their own.) Different systems determine their position by different means. INS measures changes in acceleration in three dimensions based on a known starting position. Older systems used known VOR and/or DME facilities being received to calculate position, and, of course, GNSS uses satellites.
With these navigation capabilities in mind, fixes were established on many instrument approach procedures to allow aircraft to navigate directly to final on their own. These were often called Intermediate Fixes as they signified the beginning of the intermediate segment of the approach procedure, and are typically located between 8 and 15 miles on final to coincide with the distances set up for completion of the procedure turn to final by conventional navigation. The idea was that the pilot can set the aircraft up to fly directly to one of these fixes and either turn the aircraft or let the autopilot do it automatically, onto the final approach course to begin the instrument approach procedure as a straight-in approach, just as if the aircraft had flown a DME arc or having been vectored to final as the transition. The big thing here is that the pilot must maintain situational awareness to ensure a suitable altitude for the segment of flight. DME arcs and other published transitions have altitudes published for each segment, but flying directly to an IF requires a little more thought. See my earlier article on IFR Altitudes - Cruise and Descent for more information on this topic.
Of course, the more GNSS proved its accuracy, reliability, and repeatability, the more these systems were exploited until we see a multitude of GNSS-based approach procedures with no underlying ground-based NAVAIDs whatsoever. Since all the references waypoints are "points in space" and unreliant on anything on the ground, they can be designed almost anywhere and the geometry can be refined to avoid restricted airspaces, obstacles, spotty terrain, and so forth. Aircraft can, essentially, from any angle of approach to destination navigate the aircraft to final by flying a series of waypoints. Required Naviation Performance (RNP) systems can be capable of flying arced segments to final, potenially shaving upwards of 10-12 miles off a an aircraft's approach to airport by turning the aircraft from downwind onto final in a continuous, curving path to join a short final approach segment. Fewer miles flown, less time in the air, many litres of fuel saved. At the project I headed at Halifax published in November 2016 reuslted in an estimation of having saved over 22,000 NM of flight by the operators equipped to fly them in the course of the first year -- all of that with only 25% of operators being so-equipped.
The more time went on, the more the equipment and the airspaces were refined. Busier airports already had Standard Terminal Arrival Routes (STARs) to help organize traffic flow. RNAV STARs are the latest incarnation. Designed primarily for aircraft equipped with Flight Management Systems (FMS), these transitions involve a series of fixes placed strategically to align the aircraft with an approach procedure, or multiple approach procedures of different types, and usually serve to carry an aircraft on transition routes to each runway at an airport served by an IAP. Typically, a waypoint is used as an entry point and a path determined strategically to manage air traffic (with respect to other arrivals, departures, or a combination) and the transition begins there. There may be published altitudes and speeds at various points that must be observed, all in the name of sequencing and separating aircraft as they manage their own descent paths, in theory with a minimum of ATC and pilot intervention.
If ATC simply clears a pilot "for an approach", the pilot has the choice of doing any published Instrucment Approach Procedure (IAP), and may set up for that procedure by using any of the transitions described above. Once in receipt of such a clearance, the pilot now has a responsibility to inform ATC as soon as practicable of the type of approach intended. The constraints to be adhered to include that the pilot use only published IAPs (Visual and Contact approaches are not allowed without expressed permission from ATC) and that the pilot must not deviate from the approach he stated to ATC without prior permission from the controller. The pilot is responsible for terrain and obstruction clearance while navigating under these circumstances.
Lastly, I already discussed Contact and Visual Approaches in another topic, so I'll only mention that under certain weather conditions, ATC may approve a pilot's request for a contact approach, or clear an aircraft for a visual approach once traffic conditions permit. If, as above, the controller clears a pilot "for an approach" and the pilot wishes to do a Contact or Visual Approach, the pilot need only ask. It's likely that the controller will be able to approve the request since other traffic is not likely to be a factor if the controller was willing to clear an aircraft unrestricted in the first place. Please refer back to the Archives for the discussion on Contact and Visual Approaches.
Not all instrument approach procedures result in a landing on the runway aligned with the approach aid. For that matter, not all approaches are aligned with the runway they serve. Even some RNAV approaches use unaligned final approach segments to get around obstacles. At many airports, the only way to design an approach was to align the final approach course at an angle to the runway. Sometimes a small angle, other times it could be as much as 90° to the runway. The weather may dictate a landing on a runway for which there is no IAP (or no serviceable NAVAID). In these cases, the pilot may be able to conduct a circling procedure from an IAP.
It's worth mentioning at this point that, due to the efficiency and general availability of RNAV IAPs, the "Circling Minima" line has been removed, effectively removing authorization for a pilot to conduct a circling approach following an IAP. This means that an IFR pilot may have to "Cancel IFR" to be legal to stray from an IAP's paths and land on another runway. Typically, at least one approach procedure that uses a "traditional", ground-based NAVAID will keep a circling procedure at the airport. While not idea, it makes the airport useful for those who cannot fly RNAV IAPs.
There are different weather minima for a circling approach than for a straight-in approach. Typically, a higher ceiling and higher visibility are required for a circling procedure. The idea is that an aircraft completes an approach procedure as a cloud breaking maneuver and then, once visual with the field or at least the airport environment, the pilot flies the aircraft so as to land on a runway not aligned with the course just flown.
If cleared for a Circling Procedure, the pilot must still complete the instrument approach procedure commenced under the approach clearance. In the event of an unrestricted approach, the pilot must fly the approach procedure stated to ATC. How long must the pilot remain on this procedure before commencing circling? First off, the aircraft must be clear of cloud and have enough forward visibility to see the runway environment, and be assured of keeping the runway in sight. The area for circling is described as an area bounded by arcs drawn around the thresholds of all runways at the destination airport, and these arcs connected by tangent lines. See the diagram below.
The category of aircraft is determined by its speed on final. Category E aircraft would, in this case, include little more than jet fighter aircraft. Most would fall into Category D or less. The idea here is that the pilot must follow the published procedure until the aircraft is within this area shown above. Then the circling maneuver can begin for the intended runway of landing. Exaclty how this must be flown must include considerations for other traffic already operating around the airport, what ATC had stated in the clearance for the circling procedure, terrain and obstructions, noise abatement procedures, and so on.
When the weather is bad, there exists the possibility of being unable to complete the approach to a landing. In order to land, the pilot must make, and maintain, the visual reference to the runway environment. This visual reference could include one or more of the following:
Anything that the pilot can use to positively identify the landing area and safely complete a landing is useable. If the pilot can't make visual contact with the runway environment by the time the aircraft reaches the Missed Approach Point (MAP), a missed approach must be executed, following either the missed approach procedure as published on the IAP itself, or as overriden in alternate missed approach instructions issued by ATC.
The Missed Approach (MA) procedure is published on the approach plate. Unless the pilot receives alternate missed approach instructions from ATC, this procedure must be followed, or the pilot may, weather permitting, Cancel IFR and continue on as desired. Pilots are responsible for initiating the missed approach procedure at or before the Missed Approach Point (MAP), since obstacle clearance is not assured if the missed approach is commenced after the MAP. The MAP is published on the approach plate, and in the case of an ILS or other approach procedure with a "glide slope" presentation (aka known as a "Precision Approach"), it is coincident with the Decision Height (DH). If the runwayenvironment is not sighted by the time this altitude is reached, the must go around. As soon as practicable after initiating a missed approach, a report of such activity should be made to ATC.
In the event that Alternate Missed Approach instructions are received, the pilot, upon acknowledgment of the clearance, is responsible to ensure obstacle and terrain clearance is me before beginning any assigned maneuverst. To remind pilots of this requirement, Canadian ATC will normally issue alternate missed approach instructions that contain a turn with a phrase like, "when able," preceding any turning instruction. When in receipt of alternate instructions, a pilot shall not fly the published missed approach. ATC will be basing separation between aircraft on the assigned missed approach instructions being complied with. A pilot need not accept alternate instructions; they may be refused with a request for something different. Once they are read back correctly, they are like any other clearance and ATC will take the readback as acceptance.
At airports where ATC is unable to provide clearances for simultaneous approaches, ATC must protect for the missed approach. If the missed approach procedure contains authorization for pilot #1 to climb to 3,000 feet, ATC shouldn't, without some other provision in place, clear pilot #2 below 4,000 feet until the #1 aircraft is no longer a factor. #1 is considered "not a factor" once it has landed, cancelled IFR, or is established in a missed approach that provides separation from the final approach course #2 will be using.
Good airmanship includes the practice of advance notice of intent if the possibility of a missed approach due to weather conditions exists. If the weather is such that a missed approach might occur, the pilot should inform a controller of plans in the event of a missed approach so ATC can plan the flow of traffic. It may also benefit the pilot in that alternate missed approach instructions can be issued, time permitting, to provide a pilot with a better clearance than the published missed approach.
There is a lot of information to come forward for IFR arrivals. One of the biggest sections of our beloved AIM for IFR flight in the RAC section is geared for IFR arrivals. More detail of some of the above mentioned items can be found in future articles. If there is any question that you want answered, please let me know. You can e-mail me directly at mo@xlii.ca. Thanks for reading!