AOPA will be closing at 2:30 p.m. EDT, August 29th, in observance of the Labor Day Holiday. We will reopen on 8:30 a.m. EDT, Tuesday, September 2nd.
March 1, 1998
By Peter A. Bedell
One of the advantages of becoming a proficient instrument pilot is the satisfaction of performing a smooth, error-free flight in conditions that are anything but perfect. As any good pilot — IFR or VFR — knows, a flight like this won't come off without a hitch in the absence of good flight planning. Because they are flown in visual conditions, VFR flights generally require less flight planning (except in those cases where airspace wreaks havoc on your VFR route). Therefore, the thought of obtaining a set of IFR charts is pointless, right? Not exactly.
IFR charts provide a surprising amount of information to the VFR pilot, especially one flying above mountainous terrain. In many cases IFR en route charts are harder to read than their VFR counterparts, but their lack of cartographic features leaves room for other information helpful to pilots — IFR or not.
Planning a hypothetical flight on a VFR chart from the Springdale (Arkansas) Municipal Airport to Memorial Field in Hot Springs, Arkansas, we see the usual load of helpful information on terrain with several visual checkpoints to reference along the route. On that VFR chart you will also find quite a bit of IFR information that is helpful to the VFR pilot. For example, Victor 527 is clearly visible on the VFR chart, providing what is a direct shot to Hot Springs (see page 65). It even shows the name and total mileage of that airway segment somewhere near the middle of the route. Other helpful bits of IFR information on the sectional that are easily digested by the VFR pilot are the printing of the inbound bearing from the Hot Springs VOR and the major intersections along the route. With all of that information, who would need an IFR chart?
It's certainly not obvious, but reviewing the same route segment on the IFR chart reveals some interesting things that would otherwise be unavailable in planning your flight strictly with the VFR chart. On the IFR chart, we lose the cartography but pick up a lot more detail in terms of leg lengths, communication frequencies, and recommended altitudes.
Between waypoints on our imaginary flight plan, the IFR chart has quick references for determining leg lengths. This information can greatly aid flight planning and provide excellent cross-references for VFR en route checkpoints. For example, on our VFR flight, if everything has gone as planned and you are on course passing over the private airfield labeled "Cedar Creek," you should also be 42 miles out of Hot Springs. If your airplane is equipped with DME, this position will be confirmed — provided the DME is receiving a good strong signal (more on that later). If there is a second VOR receiver on board, you can triple-check your dead reckoning by tuning in the Fort Smith VOR, dialing in the 105-degree bearing on the omnibearing selector (OBS), and identifing that you are at the DANIL intersection. Of course, if you fly with a loran or GPS, this discourse may seem like overkill. But savvy VOR operation cross-referenced with good chart skills will come in handy when your GPS or loran decides to pack it in. Just having a finger on a chart and all of your old-fashioned radios locked on to nearby stations beats the panic that sets in when you're doubting your position or just plain lost.
Perhaps the greatest advantage to using IFR charts is their help in altitude planning. Our route from Springdale to Hot Springs is a great example for showing the importance of altitude with regard to terrain clearance and radio reception. On the IFR chart, Victor 527 has several altitude references for different segments of the route. Between WESTY and CASKS intersections, the altitude noted along the airway is the minimum en route altitude (MEA), which is 4,000 feet. The MEA assures that you have at least 1,000 feet of terrain clearance while established on that airway segment. (Airways are generally eight miles wide.) Flying at the MEA also assures reception of usable navigation signals from the VORs or nondirectional beacons, depending on which type of navaid defines the route.
Between CASKS and SCRAN intersections the MEA rises to 6,500 feet. The asterisked 3,500-foot designation is the minimum obstruction clearance altitude (MOCA). This altitude provides terrain clearance only but does not guarantee navaid and/or communication reception. The VFR pilot who planned with only a VFR chart and is cruising at 3,500 feet may wonder why he can't receive the Razorback or Hot Springs VORs — the reason being, of course, that VOR reception is line of sight and the mountains in this area block the signals from reaching the aircraft. One hopes that the VFR pilot's dead reckoning skills aren't too rusty, or that there is a GPS or loran to keep the aircraft on course.
IFR pilots may descend to the MOCA only when within 22 miles of the VOR to which they are navigating. In our example, the MOCA is basically a reference altitude since the pilot is not within 22 miles of any VOR. In the case of an emergency, such as icing, the IFR pilot can be assured that he has terrain clearance if he descends to the MOCA. If the pilot is in radar contact and does not feel an emergency is at hand but would like to descend to (hopefully) better conditions, the controller may approve a descent to the minimum vectoring altitude (MVA). That altitude is up to the controller, given the aircraft's position on the airway, but it will probably be somewhere at or above the MOCA.
At SCRAN intersection the MEA vaults up to 9,500 feet even though terrain tops out at just over 2,000 feet. You may also notice at SCRAN the "MRA 3,300" note. This means that the minimum reception altitude to identify that intersection with the two VORs is 3,300 feet.
It is worth noting here that these minimum altitudes for IFR flight are references for the IFR pilot. Although they are helpful to the VFR pilot in choosing an altitude, the hemispherical rule for VFR cruising altitudes still prevails. For example if the MEA is 4,500 feet on an eastbound airway, the VFR pilot should still plan to fly at 3,500 or 5,500 feet msl.
At the DANIL intersection, another common symbol on the IFR chart denotes the changeover point (COP). In general, instrument pilots navigate from one VOR until the halfway point of the airway. At that point he would switch to the VOR to which he is navigating. However, in mountainous areas, or in other places where VOR signals can be degraded by some other influence, a COP is used to tell the pilot to change navaids sooner or later than the normal halfway point. In the case of our route, we should navigate via the Razorback VOR until 75 miles out. At that point we switch to Hot Springs, which is 42 miles ahead.
IFR charts also provide communication frequencies not found on the VFR chart. How many times have you been flying along VFR and wanted to receive radar advisories from a controller — but didn't have a clue as to who the controlling agency would be or what frequency to try? Along our route, the IFR chart has a postage-stamp icon just east of the "V527" label. This stamp denotes Memphis Center's communications frequency in the Fort Smith area. If you don't want to carry IFR charts with you, simply jotting these frequencies down on your VFR chart will come in handy should the desire (or need) to call ATC arise. IFR en route charts also show ATC sector boundaries and can be helpful in determining the controlling agency on your particular route.
So are we telling you to go out and spend hundreds of dollars on an IFR chart subscription for your VFR flight? By all means, no. However, a recently expired set from an instrument pilot friend would be great for planning purposes at the home or office. Current charts are optimal, of course; but if they are used strictly for planning purposes, a set of expired IFR charts will make a great addition to your flight-planning arsenal. In addition, getting familiar with the IFR charts during your VFR days will make instrument training exponentially easier.
MOCA — Minimum obstruction clearance altitude. The lowest published altitude in effect between radio fixes on VOR airways, off-airway routes, or route segments that meets obstacle clearance requirements for the entire route segment and that assures acceptable navigational signal coverage only within 22 nautical miles of a VOR.
MRA — Minimum reception altitude. The lowest altitude at which an intersection can be determined.
MEA — Minimum en route altitude. The lowest published altitude between radio fixes that assures acceptable navigational signal coverage and meets obstacle clearance requirements between those fixes.
MVA — Minimum vectoring altitude. The lowest altitude (in msl) at which an IFR aircraft will be vectored by a radar controller, except as otherwise authorized for radar approaches, departures, and missed approaches. The altitude meets IFR obstacle-clearance criteria. It may be lower than the published MEA along an airway or high-altitude jet-route segment. It may be utilized for radar vectoring only upon the controller's determination that an adequate radar return is being received from the aircraft being controlled. Charts depicting minimum vectoring altitudes are available only to the controllers.
COP — Changeover point. Marked on an IFR en route chart to denote the point at which to switch from one VOR to another.
MSA — Minimum safe altitude. Altitudes depicted on approach charts which provide at least 1,000 feet of obstacle clearance for emergency use within a specified distance of a navigational facility upon which a procedure is predicated.
MAA — Maximum authorized altitude. A published altitude representing the maximum usable altitude or flight level for an airspace structure or route segment. It is the highest altitude on a federal airway, jet route, area navigation route, or other direct route for which an MEA is designated at which adequate reception of navigation aid signals is assured. Be aware, though, above the MAA it is possible to tune in a faraway station that has the same frequency as the desired navaid.
IFR speak — When making your initial call to ATC for VFR advisories, try to reference your position from a prominent IFR waypoint. Since controllers are routinely dealing with airliners and are immersed in the IFR system, they will be much more familiar with an intersection instead of simply, "I'm north of XYZ VOR." In addition, the controller might think you are a more experienced instrument pilot if you are familiar with those fixes. Remember to keep your radio calls brief and succinct; give the controller only the information he needs. If all works well, he may not tell you to "remain clear of the area."
Special VFR — Has weather dropped below standard VFR minimums of a 1,000-foot ceiling and three miles' visibility in the local area but you know it's clear along your proposed route? If there is no note on the chart saying "Special VFR not authorized," you may request a special VFR clearance from the tower or controlling facility to proceed out of the area. If approved, you may operate in visibilities as low as one mile, although we wouldn't recommend it in visibility that poor. Special VFR is permitted within Class B, C, D, or E airspace only. If operating at night, you must be instrument-rated and the aircraft must be equipped for IFR flight. Once clear of the area, ATC no longer has to provide separation services to you, so be doubly sure that the weather is going to clear.
Visit an ATC facility — There is no better way to understand what happens on the other end of the mic than to see it firsthand. There you will see why controllers may need to restrict your altitude in certain areas and learn why your clearance is nothing like the flight plan you filed. Most likely the controller will allow you to plug in a headset and listen in to what's going on as you watch the scope. Call a nearby center or approach control and ask for a tour. Phone numbers for U.S. territory ATC facilities are listed in the 1998 AOPA's Airport Directory on pages 1-28 to 1-30.
Links to all Web sites referenced in this issue can be found on AOPA Online. E-mail the author at email@example.com.
FAA Information and Services,
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