The Unflyable Clearance

ATC Controllers are a sharp group of people that guide us unerringly-most of the time. But human and automation frailties can make for problems.


14 CFR 91.123 says, “When a pilot is uncertain of an ATC clearance, that pilot shall immediately request clarification from ATC.” Complying with the reg seems easy enough, but under pressure of time, heavy weather and busy controllers we are tempted to assume that ATC knows its intentions and to accept a clearance as given. Egregious errors appear quickly, subtle ones less so.

In developing this article I asked perhaps a hundred IFR pilots, “Have you ever been given an unflyable clearance and if so how did you resolve it?” Only a few could recount a truly unflyable clearance, which I take to mean cannot be physically flown, is illegal or dangerous. More common were cases of flyable but illogical, inconvenient and even dangerous clearances.

Clearance With No Limit

I was occupying the right seat in a Cessna 421 on an IFR Angel Flight. The owner in the left seat was an experienced, savvy pilot. This was good because I had never been in a 421 before.

ATC cleared us to an intersection short of our destination. I was unconcerned because I think of flying at 110 knots, not 160. Surely ATC knew we needed further clearance, but no, in a heartbeat we reached our clearance limit with no place to go next. We had fallen off the end of the IFR earth.

The rules say to hold at a clearance limit, but the pilot flew beyond it on his present heading while he scrambled to get further clearance. I was sure that ATC was doing a little scrambling of their own. Soon we received further clearance and were on our way, but this event was handled poorly by ATC, the pilot and me— who should have spoken up sooner.

Name Changes

Another pilot said he was cleared to the Vero Beach (VRB) VOR, but there was just one problem. The VOR’s name had very recently been changed to the Treasure VOR with a new identifier, TRV. His G1000 knew this but neither he nor ATC’s clearance machine did. When he entered VRB into the flight plan, the G1000 refused it. Before nagging ATC, he used the MFD cursor to scroll up to what used to be VRB and found the error. He added wryly, “No point in looking foolish to ATC if you can avoid it.”

I found several similar instances of intersections issued that no longer existed. The controllers had been giving out the deleted intersection for so long that they erred through force of habit.

Controllers are almost always, but not invariably, cooperative. One controller insisted a pilot accept an over-water clearance that the pilot refused several times. In exasperation, he declared an emergency. The controller responded, “Say the nature of your emergency.” “Your clearance.” came the frustrated reply.

Wrong Directions

Another pilot was being vectored for an ILS approach. He was told to fly a southeasterly heading when the localizer was northeast. It turned out that the controller was vectoring him for an ILS at another airport. The pilot did not catch the error, but I did because I anticipated a northeasterly heading. Maintaining situational awareness tells you where you are and about what heading you can expect next.

I had a similar disappointment when given an incorrect vector away from an ILS localizer. I queried the controller but he didn’t want to be bothered and switched us to tower. I joined the localizer anyway, called tower and no one said a word.

Automation Surprise

Unflyable clearances can also be the work of automation accepted without question. For example, several web-based flight planners will take you from Palm Beach County (KLNA) right over the top of Palm Beach International (KPBI) to join V3 northbound. It looks nice, but ATC will never permit you into the inner ring of the Class C to join an airway. Instead, you will be vectored around the Class C to join the airway north of the airport.

Accept a preferred route with caution. Canned routes know nothing about malfunctioning facilities. Controllers may catch the error or not. Briefing NOTAMs will inform you of inoperative en route and terminal facilities.

Similarly, a G1000 is unaware of Special Use Airspace or altitudes with respect to its flight plans. It will cut a nice magenta line right through a TFR or a mountain, no problem. Theoretically, ATC will either not give, or will coordinate clearance through, SUA. But it’s always best to ask if it’s hot. It’s up to you to avoid flying at an unsafe altitude if off airways. To be safe, I use the published OROCA or higher.

Some unflyable clearances have blatant flaws, while others have subtle discontinuities. Departures seem ripe for unflyable clearances as in the case where no heading is given after takeoff. Another example is when the pilot is expected to join an airway without ATC specifying an associated fix, or when the pilot is anticipating radar vectors while the controller expects the pilot to fly the departure on his own.

Pilots told me they have been given clearances beyond their fuel range, some required performance or navigation beyond the airplane’s capability, and other clearances had designated inoperative navaids which is another good reason to check NOTAMs.

Flexibility of GPS

Controllers today seem to assume that all aircraft have GPS. One pilot was given a clearance direct to an intersection, which was impossible without GPS. She had not filed /G because her GPS was VFR only. Yet the controllers insisted, so she confirmed the GPS heading and distance with ATC and off she went.

Most controllers are not pilots and hence may not be able to recognize an unflyable or illegal clearance. In the end, we are the final arbiters of what is flyable and legal.

The Inconvenient And Illogical

A pilot friend flying a Beech Duke was given a clearance for a northwest departure from Vero Beach (KVRB) to Palm Beach International (KPBI), some 60 miles due south. Oops. Adding insult to injury, ATC wanted to send him southeast to SURFN intersection that is way out over the water and would have added another 50 miles to his trip. He told ATC the magic word, unable and ultimately received a clearance he could safely fly.

When we return IFR from the north looking to land at KLNA just south of KPBI, we are usually diverted way to the west to cross the Pahokee VOR. One day I used the time-honored, “Time for a question?” to ask ATC why.

It turns out that PBI has a Letter of Agreement with Miami TRACON not to permit IFR overflights of PBI within its Class C. Hence your illogical clearance may be the result of such an agreement between adjacent facilities. LOAs are not published, but your unreasonable clearance may be the result.

Weather permitting, I cancel IFR and stay with ATC for advisories. Almost always they take us over the top of PBI and straight into LNA.

A perfectly correct clearance can become inconvenient if not unflyable if an amendment is complex and is read to you at machine-gun speed as in congested busy airspace. One professional pilot flying a Beech C-90 in the New York area told me that they had a mad scramble to enter a complex amendment into their equipment, which they made, but that it would have been so much easier to send them to a nearby intersection and then fly on.

The cure for this is to slow the aircraft, ask for a delaying vector or ask the controller to “say again slowly” or say “unable.”

Are you IFR?

At non-tower airports you can expedite the process by departing VFR (when conditions permit), clearing the pattern and requesting the filed clearance airborne. You will be given a squawk, asked to ident and to remain VFR. Once identified, and given an initial altitude and heading—unless ATC again adds remain VFR you are IFR as ATC has taken responsibility for obstacle clearance and navigation —a full route clearance soon follows. However, in busy airspace ATC may send you to the FSS for the clearance.


There is occasional confusion and even sloppiness in the way, when and why holds are issued. One of my cohorts was issued a hold 85 miles away and far off route—you may query ATC for the reason.

Sometimes controllers delay issuing an EFC time. Without one, if communications are lost, the pilot will not know when to depart the hold.

Several pilots mentioned pop-up holds. The Controller’s Handbook (Section 4-6-1) says that a hold should be issued at least five minutes before the aircraft reaches the holding fix. If the fix is less than that, instructions should be given immediately. Rather unnecessarily it adds that if within the five-minute period, instructions should be given immediately. AIM 5-3-7 (d) adds that pilots should begin reducing speed 3 minutes from the fix so as not to exceed maximum holding airspeed. I bet that many readers have been given holds with only a few minutes warning, especially on approaches.

While the AIM expresses a strong preference for published holds, the Handbook simply notes that most generally used holds are charted.

Summing Up

Read back all clearances carefully and fully. A way out for lost communications is always a factor in any clearance.

The Beech C-90 pilot stressed that the radio is your “lawyer, savior and insurance policy” against a violation because the burden of proof is always on you. Fortunately, most unflyable clearances if not caught result in a violation, not an accident.

Fred Simonds is a Gold Seal CFII, check airman and factory-certified G1000 instructor. See his web page at

This article originally appeared in the April 2013 issue of IFR Refresher magazine.

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