Aviation Topic of the Week
By Michael Oxner, March 7, 2004


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This week's topic:
IFR Flight Example, Part 6: Descent & Approach

Now that our pilots have made it enroute, it's time to start thinking about descent. We have a few items to cover this week, so let's get right to it.

Landing Information
ATIS, With Our Example
Commencing Descent
Over to Terminal
Vectors for the Approach
Getting on Final

Landing Information

Whenever a pilot goes flying, he has to know several things. Not the least of which is the weather at destination. This sort of thing should be obtained prior to departure as part of a complete weather briefing, which includes the forecast (should one exist) for the destination aerodrome. Our pilots had received a complete weather briefing, and part of their package included the following for CYHZ.

METAR CYHZ 251300Z 19006KT 3SM BKN008 OVC015 M03/M06 A2943
RMK SC6SC2 SLP965=
 
METAR CYHZ 251400Z 20015KT 1SM BKN008 OVC015 M03/M07 A2942
RMK SC6SC2 SLP962=
 
METAR CYHZ 251500Z 21015G25KT 1/2SM VV004 M05/M08 A2941
RMK SN8 SLP958=

TAF CYHZ 251143Z 251224 22015G25KT 1SM -SN BLSN BKN002 OVC005
FM1700Z 22020G30KT 1/2SM -SN BLSN VV002
FM2200Z 30015G25KT 1SM -SN VV005
RMK NXT FCST BY 18Z=

The weather at CYHZ is forecast to be dirty, like the forecast for CYJT. The difference is that we beat the weather out of there. Halifax is looking at some light snow and blowing snow, giving a low ceiling (in the form of "vertical visibility", meaning there is not likely to be a real ceiling to the clouds under which visibility is better) and low visibility. The latest weather observation (the 1500z) at the time the briefing was issued has winds out of the southwest (230° magnetic) at 15 gusting to 25 knots. One could easily figure on some light to moderate turbulence on approach, both from the gusts and the likely existence of mechanical turbulence from the wind speed alone. Given the fact that snow is falling and blowing around, it's also quite likely the runway will be somewhat less than 100% bare and dry.

In any case, the pilot needs to have current weather and runway conditions, and he also has to know what approach to expect. ATC MANOPS, the controller's guidebook, has a section on landing information and what controllers are expected to provide. I'll let you refer back to the article written on that topic by clicking here, if you're interested. For brevity, this includes runway and approach in use as well as current ceiling and visibility, among other items. ATC is supposed to inform pilots of these items before or shortly after a pilot commences descent. That way, if the weather is questionable (or worse), a pilot has the information required to make the decision to head to his alternate before he gets all the way down to approach altitudes and has to climb back up.

ATIS, With Our Example

In our example, the destination airport (CYHZ) has an ATIS. This stands for Automatic Terminal Information Service. A recorded message is broadcast over a defined frequency, and this message normally contains the latest weather sequence (includes weather specials), runway in use for landings and departures (may be different runways for each), the IFR approach in use (a pilot may still request an alternate approach if required), and pertinent airport conditions (like runway surface conditions, Canadian Runway Friction Index, etc). Often included in the ATIS are other items like NOTAMs for the airport and local area, which includes equipment outages. This message cycles over and over, so if you tune in part way through, continue listening for the full message. Most ATIS machines in Canada are now a digitally produced message, synthesized by software in the TWR which interprets the weather sequence and generates the message with sound bites pre-recorded by a guy named Steve. The message sounds a lot like one of those disjointed phone messages you get when you call a company and are sent through an automated "press 1 to speak with service" sort of systems. ATC has the ability to add extra items and they can even record a message that the system can't process on its own to make sure all pertinent information is available. Many of these systems have a phone number published in the Canada Flight Supplement so an interested party can use the phone to dial in to the message and get the details before getting in the plane.

Just as departing pilots are supposed to listen to the ATIS and make note of the identifying letter in the message before calling ATC for clearance or taxi, arriving pilots should be tuning in the ATIS prior to beginning descent. The AIP RAC 9.1 refers to obtaining ATIS broadcasts, and it says that "pilots should use it to obtain the basic information as soon as practicable." For an arriving aircraft this could be interpreted to match ATC's requirement mentioned above, around the time descent will begin. It is best to get the information prior to contacting the arrival controller if a Terminal Control Unit (TCU) which serves the destination airport is in operation.

So now our pilots will tune in the ATIS. Where do they find the frequency? In a couple of places, actually. The entry in the Canada Flight Supplement for CYHZ has it listed in the COM section, and all of the approach plates (including the airport diagram and the SID) in the Canada Air Pilot have it listed in the frequency bar across the top of each chart. In the case of CYHZ, it is available on 121.0. When tuned up, our pilots hear Steve's voice say this:

ATIS: "Halifax International Airport information MIKE, weather at one six zero zero zulu. Wind two four zero degrees magnetic at two zero gusting three zero. Visibility one half mile, light snow, blowing snow. Vertical visibility three hundred feet. Temperature minus two, dew point minus four. Altimeter two niner four two. IFR approach, ILS runway two four. Category two ILS runway two four available. Landing and departing runway two four. Runway surface condition report issued at one six four five zulu: runway zero six-two four a one four zero foot centerline three zero percent bare and dry, five zero percent compacted snow, two zero percent ice. Remainder loose snow up to one eight inches. Runway one five-three three a one two zero foot centerline two zero percent compacted snow, eight zero percent loose snow up to four inches. Remainder 100 percent loose snow up to two four inches. Advise ATC on initial contact you have received information MIKE."

If you recall from last week's topic, the time by YQY was 1633z. The KingAir would take about 40 minutes to get from Sydney to Halifax in level flight, so by the time they get near, the 1600z sequence would be the latest unless a special were put out. Certainly the runway report is about as current as it will get, considering the time it was issued. In this case, it appears as though the crews are working to maintain at 140 foot centerline on the runway, and the wind might actually be helping out by sweeping the snow off the runway before it has a chance to settle. The drifting snow is more the problem now, since where the snow does settle, it can be deep. For out pilots, the wind is right down the runway, which means no crosswind to contend with. This is good, since drifting outside the 140 foot centerline means an encounter with a "windrow" of up to 18 inches. This is analogous to what a snowplow will leave in your driveway as it plows your street during a storm -- not something you'd like your gear to hit at 100 knots, and certainly not something you want your propeller blades to hit at all.

Commencing Descent

For our example flight, the pilots have been told to request descent on 135.3. They've been tracking the YQY VOR on NAV1 and VOR1, and YHZ on NAV2 and VOR2. They're at 12,000 feet, and they make the decision on when to descend. A topic has been written on this subject almost a year ago, and it's not a bad read. If you want more information on that, click here. They complete their pre-descent checklist, and are ready to start down, so the conversation continues on the radio with:

FART: "Moncton, Alpha Romeo Tango request descent."
CZQM: "Alpha Romeo Tango descend to one zero thousand, Halifax altimeter two niner four two."
FART: "Two niner four two, Alpha Romeo Tango out of one two thousand for one zero thousand."
CZQM: "Alpha Romeo Tango, roger. Contact Halifax Terminal now on one one niner two. Good day."
FART: "Over to one nineteen two. So long."
One of my pet peeves as a controller is a pilot not doing the courtesy of acknowledging a frequency change. While the majority of pilots will say at least something, some will just change over and make contact with the new unit without letting the last unit know they heard the radio call. This leaves the preceding controller wondering if the pilot heard the transmission. Without the acknowledgment, the controller has to call again. After a few unsuccessful attempts, the controller will normally end up calling the next controller to see if the pilot checked in. Neither controller wants to take up valuable time doing this "com search". Nothing complex is required since there are no special rules as to a frequency change readback. Just a simple something to let ATC know the frequency change was received so they don't have to go looking for you.

Over to Terminal

FART: "Halifax Terminal, good day, KingAir Foxtrot Alpha Romeo Tango with you leaving one two thousand for one zero thousand."
CYHZ TCU: "KingAir Foxtrot Alpha Romeo Tango, Halifax, ATIS MIKE, altimeter two niner four one. Vectors ILS runway two four, fly heading two seven zero. Descend to six thousand at pilot's discretion."
Our pilot forgot to mention to ATC that he has ATIS MIKE, so ATC has to tell him what the current letter is. This is one way ATC can confirm the pilot has the latest information so he doesn't have to read it out on a busy terminal frequency.
-Oh, by the way. Did you catch that HZ TCU gave a different altimeter than CZQM? There are a couple of possibilities. First, the TWR and TCU controllers have up-to-the-minute data on the airport they serve, while the ACC might not. There may be pressure changes since the issuance of the last sequence. Even if the ACC does have the same data, just the time that elapses between one controller reading the display and another controller reading it might be enough for a change, especially in a rapidly changing weather system. In either case, it's just a matter of the controller reading what he has in front of him at the moment.
FART: "Yes, sir, we have ATIS MIKE. We're descending to six thousand and we'll turn right to heading two seven zero. Alpha Romeo Tango."
CYHZ TCU: "Alpha Romeo Tango, roger. Keep the speed up as long as able."
FART: "Alpha Romeo Tango."

There has been much discussion regarding the last phrase from ATC, "Keep the speed up". Does this provide pilots with the authorization to exceed 250 KIAS below 10,000? No. ATC doesn't have authority to waive the requirement to meet that speed limit. This phrase is simply meant to get a pilot to keep from slowing down unless necessary. At busier airports, there is often a mix of jets and props. When an aircraft in the sequence flies slower than others, either more room is required between him and the next aircraft to keep the next one from overtaking him on final, or a speed restriction on the following aircraft (which may push further back into those following him) is required. This has the effect of backing everyone up in the line, so sometimes it's easier to ask the first aircraft to run right in, leave the middles ones alone, and then slow the last ones in a sequence. Aircraft encountering turbulence may have to slow down a bit to reach their maximum rough air penetration speed, and if this has to be done, the pilots should respond when such an instruction is received, or when the slow down is required, so that ATC can make alternate plans.

Vectors for the Approach

In the last radio exchange, initial contact with Halifax Terminal, ATC initiated a radar vector to final. This was done very simply by ATC stating the heading the pilot was to fly. ATC will continue from this point to issue headings as required to get the aircraft to the final approach course. Without further transmissions from ATC, that heading should be kept, even if it has the aircraft fly through the localizer. (Note: ATC is supposed to inform an aircraft if they intend to take them through the localizer.) This suits our pilots very well, since the RNAV is on the blink anyway.

Without the RNAV, the pilots might have requested a route such as, "direct LEROS," to do their own navigation to final. In a busy terminal environment, ATC may be unable to approve such a routing. If they have other traffic to vector you around, be it departures or other arrivals they are sequencing, you may be stuck with the vectors regardless of your request. Even an aircraft flying an RNAV STAR might have to be removed from the STAR due to other traffic. Removal from the STAR is typically accomplished simply by initiating a radar vector. Once a vector is issued, the RNAV STAR is implicitly canceled, and the pilot is to continue on radar vectors, without flying any further portions, altitudes or speeds published with the RNAV STAR. If resuming an RNAV STAR is desired, ATC may initiate it, or the pilot may ask for a clearance to do so.

Any time now, since they're on vectors, the pilots may setup their NAV1 radio to the ILS localizer's frequency and set the OBS on VOR1 to the final approach course as indicated on the approach plate. Now that they're on vectors, the need to track the Halifax VOR becomes secondary at best. NAV2 was already tuned to the YHZ VOR, so this may be left there, and the ADF can be tuned to the Bluenose NDB, which serves as the final approach fix for the ILS Runway 24 approach.

Getting on Final

As time goes on, our KingAir is given further headings, altitudes, and instructions. The spaces between lines indicate some time passes between the exchanges, during which other transmissions to or from other aircraft might occur.

CYHZ TCU: "Alpha Romeo Tango, you're number four behind a Navajo. Maintain four thousand. Fly heading two niner zero."
FART: "Alpha Romeo Tango four thousand and heading two niner zero."
CYHZ TCU: "Alpha Romeo Tango, roger."

CYHZ TCU: "Alpha Romeo Tango, descend to two thousand two hundred. Reduce speed to one eight zero knots."
FART: "Alpha Romeo Tango down to two thousand two hundred and back to one eight zero."
Pilots have authority to vary within 10 knots of the assigned indicated speed. This means FART could fly as slowly as 170 or as fast as 190 while following this instruction. It is in everyone's best interests to fly as closely to the assigned speeds as practical, since ATC will assign other aircraft speeds based on what he said to you and the results he sees on his radar.

CYHZ TCU: "Alpha Romeo Tango, fly heading two seven zero to intercept the localizer and track it inbound."
FART: "Heading two seven zero to join the localizer, Alpha Romeo Tango."
This does not constitute an approach clearance. The instruction is meant to have the aircraft do exactly as told. No further descent below the last assigned altitude is authorized just yet, even if the aircraft goes through the glideslope. ATC recognizes the problems associated with trying to intercept the glideslope from above, so this normally isn't an issue to be contended with. The preciously issued speed restriction is also still in effect. There is no requirement to report intercepting the localizer, unless asked by ATC.

CYHZ TCU: "Alpha Romeo Tango cleared straight-in ILS runway two four approach. You're four miles from the Bluenose NDB, ten miles from threshold. Contact Tower now on one one eight four."
FART: "Cleared for the straight-in ILS two four and over to tower. Thanks. Alpha Romeo Tango."
The speed restriction is now canceled because an approach clearance was issued and the restriction was not re-stated. FART may now fly as fast or as slow as he desires. It might be considered poor airmanship to drop the speed right back to final approach so far out, especially if the pilots heard many other aircraft being vectored behind them.

Now our pilots tune in 118.4 and then...




Our example flight is nearing completion. With just one more segment to run, the landing and taxiing in. If you have questions, my e-mail address is moxner@nbnet.nb.ca. Thanks gain for taking the time to read!