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July 1, 2008
By Thomas A. Horne
Whether you’ve logged a lot of actual instrument time, are a rusty instrument pilot, or have a newly issued instrument rating, a review of safe IFR procedures is never out of style. That’s especially true when you’re nearing your destination. The arrival and approach phases of instrument operations demand your utmost concentration, as well as a complete understanding of the procedures at hand. That’s why we’re publishing a series of articles dealing with instrument procedures that take place close to airports; near terrain; and along arrival, approach, and departure paths.
Your preparation for arrival to an airport’s terminal area should begin early, during the latter stages of the en route phase of flight. That’s when you should get out the appropriate charts and tune in any automated weather observation system (AWOS); automated surface observation system (ASOS); or automatic terminal information service (ATIS) frequencies for weather, runway information, and notams. Depending on the airport, arrival procedures are described in standard terminal arrival (STAR), and area navigation STAR (RNAV STAR—for aircraft with IFR-certified GPS units or flight management systems). These charts set out the fixes and routes used in any arrival procedures, complete with courses, minimum or mandatory altitudes, and distances between fixes. If you’re issued a STAR or RNAV STAR, then you can expect to follow it more or less to the letter. The procedure is set down in a simplified chart form, as well as in text. To file a flight plan with an RNAV STAR after June 29, you’ll need to use an International Civil Aviation Organization (ICAO) flight planning form (see “ New IFR flight plans for GPS arrivals, departures at large airports”).
Many smaller, less busy airports away from major metropolitan areas don’t have a published STAR or RNAV STAR. For the arrival phase to these airports, you are usually given radar vectors (if radar coverage is available) or cleared to an initial approach fix in preparation for the instrument approach to follow.
Regardless of the size of the airport, the main thing is to be prepared. Review the appropriate charts to get a feel for the altitude and speed restrictions, and get ready for an ATC clearance. After you receive it, plug the procedure into your GPS (remember to double-check the name before finalizing your flight plan entry!). If you’re not equipped with an IFR-certified GPS, then start loading the string of fixes by dialing up your VORs with the published VHF frequencies and radials that make up your arrival route. Here’s where it helps to have an autopilot; while you’re entering the information and making sure your entries are accurate, let George fly.
If all this seems daunting, then you can avoid the entire STAR/RNAV STAR business, if you like. Just add “No STAR” to your flight plan’s Remarks section. For many, this is a way to simplify flight planning greatly. ATC will vector you for the arrival under this scheme, and your “STAR” will consist of a sequence of clearances—including vectors and altitude restrictions—that may in fact duplicate those of the published arrival procedures.
Your arrival clearance can take the formal route and follow the letter of the published procedure, but controllers may use vectors to modify it for traffic separation or flow control. Either way, a hint of your upcoming arrival clearance will begin with the magic word “Expect,” as in, “Expect the Westminster Five Arrival to BWI.” That’s your signal to load the proper procedure in your GPS flight plan sequence (and/or dial up the relevant VOR frequencies and radials). A formal clearance, as in, “You’re cleared to fly the Westminster Five Arrival,” should come soon thereafter.
The wording of your arrival clearance makes a big, big difference. That previous clearance (“cleared Westminster Five Arrival”) gives you permission only to navigate the arrival route laterally. A clearance that includes an assigned altitude (“Cleared Westminster Five Arrival, descend and maintain 6,000”) obviously includes an altitude assignment.
When altitudes are not published along route segments, ATC will issue you what’s called a “descend via” clearance. This “descend via” term authorizes you to navigate along your arrival route vertically and laterally. If you’re cleared to descend via a specific waypoint along the arrival route, then you’re also automatically cleared to leave your previously assigned altitude at pilot’s discretion (more on this shortly) to arrive at the next fix’s altitude as depicted on the chart. In other words, you’re cleared from then on to fly the published arrival—unless you’re issued an amendment to the clearance.
What if no altitude is published for a waypoint or fix along your route? In this case, and in cases where you’re being vectored to a fix, ATC will assign you an altitude.
As you fly an arrival procedure, you may be given more “Expect” clearances, for example, to expect a certain altitude or airspeed as your stair-step down the arrival route. But here’s an important element to remember: The Aeronautical Information Manual (AIM) states in Section 5-4-1 that the published “expect” altitudes and airspeeds—those published on a STAR/RNAV STAR/FMSP chart—must not be used in the case of lost communications. They’re only for planning purposes.
As is customary, if communication with ATC is lost, you should maintain the last assigned altitude unless you’ve been specifically told to expect certain altitude(s) as part of an ATC clearance. After that, normal lost-communications procedures go into effect. Briefly, this means to maintain the highest of the assigned or minimum published altitude, or to maintain an expect-further clearance-issued altitude. Leave your altitude at the expect-further clearance time, or, if not issued one, at your estimated time of arrival (ETA, as you indicated on your flight plan). Begin your approach descent at your ETA at the initial approach fix (the choice of approach is up to you in lost-communications situations). Begin the approach immediately if your ETA has passed.
You’ve probably heard this phrase in many clearances—not just those in terminal areas. What does it mean? It means that you’re cleared to leave your previously assigned altitude and climb or descend to a new altitude. You can start the climb or descent at any time you want, climb or descend at any rate you want, and even level off at any intermediate altitude you want. That’s the “discretion” part.
But you don’t have complete freedom. After you’ve left an altitude you can’t return to it.
Look at a STAR chart and you’ll see that some legs on the arrival route can be much shorter than others. This is where descent planning kicks in. You need to know when to begin your descent to hit a target altitude. A ballpark rule of thumb for light general aviation airplanes is the “rule of three.” To use this rule, figure out how much altitude you need to lose, multiply that by three, and drop the last three zeros to get the distance to the fix to begin the descent in minutes. Let’s say you have to descend 5,000 feet. Five thousand times three is 15,000; drop the zeros, and you get 15 nautical miles.
Luckily for those with GPS aboard, more precise vertical navigation is available from the unit’s VNAV function. Enter the desired target altitude, and these units will calculate a descent rate that will put you over the fix at the proper altitude—based on your actual groundspeed.
Of course, most airplane flight manuals come with descent planning charts in their performance sections, and these can be used to calculate times, distances, and fuel burns for descents under specified power settings.
Sometimes it’s necessary to lose a lot of altitude in a short distance. For turboprops and turbofan airplanes, this loss doesn’t usually present much of a problem. Most turbine airplanes have spoilers to increase descent rates and decrease airspeeds, their maximum flap extension speeds can be relatively high, and turbine engines don’t mind if pilots slam the power abruptly back to flight idle. Suddenly cut power on a piston engine, however, and you’re asking for damaging thermal shocks to the cylinders.
This means that piston pilots must pay close attention to power settings during those “slam-dunk” descents that ATC seems to favor. Slow, gradual power reductions are the ideal. To accomplish this, slow the airplane to its V FE (maximum flap extension speed), then let the flaps create the drag for both slowing down and descending. In airplanes with retractable landing gear, lowering the gear at V LO (maximum landing gear operating speed) can further reduce airspeed and increase descent rates. With flaps and gear out, power can be kept at levels that won’t shock-cool the cylinders—and you can reduce power at a safe rate.
By the time you’ve reached the last fix or waypoint in the arrival procedure, you should be ready for sequencing to the approach phase. ATC usually issues vectors to the final approach course, but in nonradar environments, the navigation to an initial approach fix is up to you.
Bear in mind that you could still face challenges requiring quick thinking, and quick reprogramming of your GPS and/or other navigation equipment. ATC could have left you high, so a slam-dunk plunge to the final approach course may be in your future—even though you’re close to the airport. To preclude this, you can ask for vectors to a point more distant along the final approach course, or you can ask for a turn or two around a holding pattern.
If the fates aren’t with you, then ATC may change runways, forcing you to be re-vectored for a different approach. Things can then become very busy as you reprogram the new approach, get a weather update from ASOS, AWOS, or ATIS (if any of these are available), and brief yourself for the new approach procedure. In a nonradar environment, the decision to change approaches is up to you and will most likely be based on a change in surface winds. ATC will have to approve a request to change approaches, of course, but when the wind changes, the last thing you want is a slam-dunk arrival over the runway threshold after a tailwind speeds you down the final approach course.
We’ll deal with these and other issues in the next article, which will cover the approach phase of a flight in instrument meteorological conditions. It’s a topic with enough material to fill a book (and it has!), but we’ll be sure to hit the main points.
E-mail the author at firstname.lastname@example.org.
AOPA Pilot Editor at Large Tom Horne has worked at AOPA since the early 1980s. He began flying in 1975 and has an airline transport pilot and flight instructor certificates. He’s flown everything from ultralights to Gulfstreams and ferried numerous piston airplanes across the Atlantic.
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