Aviation Topic of the Week
By Michael Oxner, June 1, 2003


Introduction
Previous Week's Topic
Following Week's Topic
Aviation in Canada Blog
Archives

This week's topic:
IFR Flight Part 5a: Arrivals

Descent for Landing
    ATC Clearance
    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.

Descent for Landing

As you get closer to destination, it follows that what goes up must go down. That would be you. With ATC around, and in controlled airspace, you should be asking ATC for descent. If you do pre-descent checklists, I'd recommend you complete these before you make the call to ATC, just in case ATC requires a prompt descent. And, as mentioned, ATC does expect you to begin descent promptly upon receipt of descent clearance unless you receive authorization to do otherwise. An example of such authorization is descent at "pilot's discretion".

When you're approaching an airport for landing, you should have all the pertinent information required. ATC has a requirement to give you Landing Information either before or shortly after you commence descent. ATC's MANOPS Paragraph 471.2 defines what ATC is supposed to give you. See the list below:

  1. Ceiling
  2. Visibility
  3. Wind
  4. Altimeter setting
  5. Pertinent remarks from current weather report
  6. If appropriate, STAR, including STAR transition
  7. Runway in use
  8. Approach aid in use
  9. Pertinent airport conditions
Pertinent information includes things like Runway Visual Range (RVR) in bad weather, 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 this kind of STAR. Normally, if an aircraft is capable of an RNAV STAR, and wants to do it, the pilot should request this in the flight plan in the route section. Radar vector STARs are alright to issue to any aircraft, and this is normal at many busier airports across the country.

At busier airports, giving landing information to individual aircraft can be troublesome at best. ATC may simply not have the time to do it. 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, 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 stating they have "Information ALPHA", or whatever letter is the current message. If ATC hears you say that, he knows you have the latest information, and he has only to issue the current altimeter setting for your destination airport.

Transition from En Route to Approach

Somewhere along the way, you have to make the transition from the en route phase of flight to the arrival, or approach, phase. There are a number of ways to do this. Remember, in each case, if ATC is online and treating the airspace around the destination airport as controlled airspace, you need authorization in the form of a clearance to navigate via any of the methods mentioned below. Simply ask ATC for what you want.

ATC may provide a clearance for a pilot to fly to an NAVAID associated with an instrument approach. At the majority of instrument approaches in Canada, an NDB is provided either as an final approach fix, or as an approach aid. Many of these are low powered NDBs and as such may only be received 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 Charlottetown NDB". In this example, the YG NDB serves as the final approach fix for the ILS Runway 03 Approach, and a pilot can conduct an approach from this facility. This would require a procedure turn.

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 depending on the direction from which the aircraft is approaching the NAVAID. More detail will be provided in a future topic, if desired. One thing that should be mentioned, just in case there isn't any further interest in this, 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 his turn to go outbound when he made the report. This is not right. The AIP 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.

In some cases, the instrument approach aid to be used is actually part of the airway being flown. Take for example the VOR Runway 27 Approach at Fredericton, NB (CYFC). There is a published transition from V300 on the east side of the Fredericton VOR to go straight in on the VOR approach from FRENN intersection.

Other transitions 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. One problem area in the real world is that some pilots believe receipt of a clearance to fly a DME arc, or other published transition for that matter, allows the pilot to descend to the published altitudes. If ATC doesn't provide you with a lower altitude with a clearance to fly an arc, you're not allowed to descend. Clearance to fly a transition is only a change to the routing portion of an IFR clearance and does not, in itself, constitute authority to descend. Clearance to fly a straight-in approach via a DME arc transition is authority to descend.

At airports served well with radar coverage, ATC may be able to provide radar 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 some areas, the lesser traveled airports can benefit from the more prominent presence of ATC radar over the last few decades. Aircraft can receive radar vectors to final in areas that previously had no coverage. Especially in the fringe areas, ATC workload has to permit this even if radar coverage does.

Advancement in 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), LORAN (though I don't believe this ever received IFR certification), OMEGA, and others. Termed Area Navigation, or RNAV for short, different systems determine their position by different means. INS measures changes in acceleration in three dimensions based on a known starting position. OMEGA and LORAN used land-based radio facilities in a similar method to what GPS does now, and some systems use combinations of VOR radials from separate facilities, or VOR and DME values, to triangulate position. GPS is the most modern of these concepts, and, if you didn't already know, it uses satellites to work out position. The benefits of GPS are far reaching, though they technically fall short of many requirements for integrity for all-phase IFR flight. There are some clever methods used to attempt to gain the integrity required, especially for the approach phase, and GPS is gaining more and more acceptance as a primary navigation tool all the time.

With these navigation capabilities in mind, fixes have been established on many instrument approach procedures to allow aircraft to navigate directly to final on their own. These Intermediate Fixes are typically located between 8 and 10 miles on final (with many exceptions in existence), to coincide with the distances set up for completion of the procedure turn to final by conventional navigation. The idea is 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 for him, onto the final approach course to begin the instrument approach procedure as a straight-in approach, just as if he had flown a DME arc as the transition. The big thing here is that the pilot must maintain situational awareness to ensure he is at 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.

RNAV STARs are the latest rage today. Designed primarily for aircraft equipped with Flight Management Systems (FMS), these transitions involve a series of fixes places strategically to align the aircraft on the final approach course. Typically, a bedpost fix is located on an airway or other commonly used route and the transition begins there. The published Standard Terminal Arrival Routes (STARs) include a flight path for each runway from the bedpost fix, and a series of fixes that either provide for a straight-in or a downwind leg, which ever is required. The fixes will often have altitudes published as well, requiring that a pilot reach the fix at or above the specified altitude, at or below, or at a hard altitude as he crosses the fix. Speeds are often published as well, intending to smooth the mix of traffic. The idea for these is that the approach profile is stored in the FMS database and the pilot simply selects which profile to fly. From there, the FMS directs the autopilot during the descent to make the published altitudes and speeds with a minimum of adjustments, theoretically allowing for the most efficient flight profile, saving fuel as well as positioning the aircraft at a point from which a straight-in instrument approach procedure can be accomplished. More in another topic later on.

If ATC simply clears a pilot "for an approach", the pilot has the choice of doing any approach procedure, and he may set up for that procedure by using any of the methods described above. Once the pilot receives such a clearance, he now has a responsibility to inform ATC as soon as practicable of the type of approach he intends to follow. The constraints to be adhered to include only that the pilot use only published approaches (visual and contacts are not allowed without expressed permission from ATC, so ask if either of these is what you want to do) and that he must not deviate from the approach he stated to ATC earlier without prior permission from ATC. Remember that the pilot is responsible for terrain and obstruction clearance while navigating under these circumstances.

Lastly, we 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. Please refer back to the Archives for the discussion on Contact and Visual Approaches.

Circling 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. 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 that is not served by an instrument approach aid. In these cases, the pilot has to conduct a circling procedure from an approach.

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, 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 he has been cleared for. In the event of an unrestricted approach, the pilot must fly the approach procedure which he informed ATC he would complete. How long must he stay on this procedure before commencing circling? First off, he 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.

VisualManeuveringArea

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 he is within this area shown above. Then he can begin the circling procedure for the intended runway of landing. Exaclty how he flies 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.

Missed Approaches

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: approach lights, runway edge lights, runway centerline lights, touchdown zone lights, VASIs or PAPIs, the runway itself, or the runway markings, etc. 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 he reaches the missed approach point, he must execute a missed approach.

The missed approach procedure is published on the approach plate. Unless the pilot receives alternate missed approach instructions from ATC, he must follow this procedure, or cancel IFR and continue on his own if weather permits. 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, it is coincident with the Decision Height (DH). If you don't see the runway by the time you reach this altitude, 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 met. To remind pilots of this requirement, ATC will normally issue alternate missed approach instructions that contain a turn with a phrase like, "when able", or "at your discretion". When in receipt of alternate instructions, do not fly the published missed approach. ATC will be basing separation around you complying with the missed approach instructions issued and acknowledged. If you don't consider the alternate instructions safe, or want something else, advise ATC as soon as possible so that other plans can be made. Simply reading back the alternate instructions indicates acceptance and compliance, just as with any IFR clearance.

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. This includes landing, canceling IFR, or the preceding aircraft being established in a missed approach that provides separation from the final approach course #2 is 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 ATC of his intentions 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 AIP for IFR flight in the RAC section is geared for IFR arrivals. I intend to provide a little more detail of some of the above mentioned items in future topics. If there is anything specific you want to see covered, please let me know. You can e-mail me directly at moxner@nbnet.nb.ca. Thanks for reading!