There is an all-encompassing rule in instrument flying, the “11th Commandment,” which says, “Thou shalt not enter IFR conditions in controlled airspace without a clearance from ATC.” A clearance, once accepted and acknowledged, is your authorization to proceed to a certain point, via a certain route, and at a certain altitude. With the majority of today’s IFR flights under radar surveillance, the clearance becomes less a separation tool and more a means of ensuring con- tinued safe operation when communications fail.
Clearances must conform to aviation’s three-dimensional environ- ment and therefore must always specify: (1) a point to which you are cleared, (2) a route by which you are expected to get there, and (3) an altitude assignment. Amendments to previously issued clear- ances may change any or all of these, but prior to entering IFR condi- tions in controlled airspace, you need all three. If the point to which you are cleared falls short of your destination airport (and this is some- times encountered because of heavy IFR traffic), one more instruction must be added: a time to expect further clearance. The same holds true for any interruption (such as a hold) in your instrument flight.
In general, pilots are required to comply with ATC clearances (or instructions) on receipt. But the controller’s use of words will provide a clue as to the timing that’s expected. Suppose Center wants you to go to a lower altitude: “Barnburner 1234 Alpha, descend to and main- tain 4000.” You are expected to acknowledge the new clearance and then begin descending; there’s clearly no urgency about this change of altitude. But when a controller says, “1234 Alpha, descend to and maintain 4000 immediately! ” you’d better be on your way down even before you pick up the mike — that controller wants you out of your present altitude right away. When there’s no traffic conflict and there’s no major concern about when to descend, you’ll hear, “1234 83
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Alpha, descend to and maintain 4000 at pilot’s discretion.” Acknowl- edge the clearance and, when it suits your situation, start down. (It’s wise to advise the controller when you commence the descent.)
So, when you hear:
“Descend to and maintain…”— Comply upon receipt. “Descend to and maintain…immediately”— Do it now!
“Descend to and maintain…at pilot’s discretion.”— Do it when you’re ready.
Copying Clearances
Time was when a pilot had to have executive secretary shorthand skills to copy a clearance like this, delivered at machine-gun speed by a ground controller with a warped sense of humor:
ATC clears Barnburner 1234 Alpha to the River City Airport via Victor 21 to the Maple intersection, Victor 418 Stone, Victor 25 to the Lewis intersection, direct Elmville VOR, Victor 182 Downy intersection direct, climb to and maintain nine thousand, cross the Hometown 23-mile DME fix at or above 4000, cross the Smithville 120 radial at or above 5000, cross Maple intersection at or below 6500, expect higher altitude at Lewis intersection, contact Hometown Center on 123.8 when established on Victor 21, squawk one one zero zero; read back.
There are several ways to handle a situation like this. You can de- velop a clearance shorthand and hope for the best, or you can sub- merge your pride and say, “Ready to copy; take it slow.” The second way is the better because it will result in fewer errors, less repetition, and more important, will contribute to a safer operation. Both parties will have a complete understanding of all parts of the clearance; mis- takes of routing, altitudes, or frequencies will stand out like an oil leak on a new paint job. Before accepting an invitation to copy a clearance at a strange airport, take a few moments to listen to other clearances and study the chart of the local area — you will reduce the element of surprise when the controller reels off some obscure inter- section or VOR.
Pilots must somehow acknowledge receipt of a clearance before it is considered accepted. Remember that Ground Control, Clearance Delivery, Center, Flight Service Station, or any ATC facility from which you might receive a clearance is people, and is subject to human error. If the controller really wanted you to proceed via Victor 47 to 84
Maple intersection but cleared you down Victor 21 through force of habit, the error might go unnoticed if you acknowledge the clearance with a simple “roger.” Just like filing an IFR flight plan over the tele- phone or from the air, you can read back most of today’s relatively simple ATC clearances with “numbers” alone. For example, when you’re cleared “to the River City Airport via Victor 21, Victor 418 Elmville, maintain 9000, contact departure control on 123.8, squawk 4032,” the readback might be simply “34 Alpha is cleared to River City, Victor 21, Victor 418 Elmville, 9000, 123.8, 4032.” And the con- troller knows you’re both in agreement on the important items.
The clearance delivery controllers at Chicago’s O’Hare Interna- tional (the busiest airport in the world) carried communications effi- ciency to a new height some years ago when they began a procedure to reduce the time required for clearance readbacks. The last item on the ATIS broadcast instructed pilots to acknowledge clearances by re- peating nothing more than the assigned transponder code — for example, “Transglobal 1465, 4356.” This put the monkey squarely on the pilot’s back because, when a controller heard that code, it was as- sumed that the clearance had been received, was acceptable, and would be complied with. This procedure seems to work quite well at other airports when outbound traffic is heavy, but a controller is completely justified in requesting a complete readback. Don’t argue; just read it back. When you use the transponder shortcut, be ab- solutely certain you have all the names and numbers straight. And just in case the controller didn’t train at O’Hare, you might make your code clearer by saying, “34 Alpha copied all, 2371.”
The nature of your IFR trips will have a bearing on the mechanics of copying clearances; if you frequently fly the same routes, your clearances will not deviate much from a pattern, and you’ll know what to expect. But when you’re trying to taxi a castering-gear taildragger in a 20-knot crosswind on solid ice, busier than a DC-3 copilot at gear- up time and wishing you had another hand and foot to help, that’s not the time to say “go ahead” when Ground Control says your clearance is ready. Tell the controller to “stand by” and, when you have the air- plane stopped in the runup area and your wits collected, indicate that you are “ready to copy.” Now you can devote yourself 100 percent to the business of copying the clearance correctly, noting changes in routing or altitudes.
And while you’re at it, why not copy the clearance in soft, erasable pencil right on the chart? It gives you a record of the clear- ance in the handiest possible place, available for instant reference as you fly, and eliminates another piece of paper in the cramped
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confines of your flight deck. You’ll find plenty of blank space for this purpose on every chart.
When the controller comes to “.…contact El Paso departure con- trol on…,” you know that the next item will be a communications frequency, and you can save more time by “writing” that frequency on the radio you’re not using. The same technique holds good for transponder codes; when the controller speaks the numbers, “write them down” on the transponder itself. Writing on radio sets and transponders makes them the world’s most expensive notepads.
Your clearance will usually come through with route and altitude just as you requested, and if you plan to fly that way again, make a note of the routing; you have probably hit on a combination that ATC will buy next time around. But if the airways you have chosen don’t fit into the computer’s assessment of the traffic situation, the con- troller will “suggest” another route. Despite what you may on occa- sion feel is an attempt to see how much out of your way they can make you fly, variations from requested routes are sometimes neces- sary. It is the controllers’ expression of the best they can do for you at the time.
Here’s where it’s good to have the enroute chart handy to see if the suggested route is compatible with you, your airplane, and the weather. Treating the clearance as a suggestion (a strong one to be sure, but still a suggestion), turn it down if you don’t like the looks of it. There may be a delay, but that’s immensely preferable to find- ing yourself loaded with ice, losing altitude, and headed toward a squall line on an airway with an MEA 5000 feet higher than you can possibly fly, all because you accepted a clearance that you didn’t want. Always refuse a clearance that will fly you into trouble! This philosophy assumes your complete knowledge of existing and fore- cast weather conditions along the route.