Cannot Comply with an ATC Clearance: Unable



When you cannot comply with an ATC clearance, the magic word to use is “unable”. Simply saying “unable”, and nothing else, might not get you completely off the hook with ATC. I’ll explain why, and what to do about in this month’s edition of IFR Flight Radio.

Show Resources

From the Aeronautical Information Manual’s Pilot/Controller Glossary:

UNABLE− Indicates inability to comply with a specific instruction, request, or clearance.

§ 91.123 Compliance with ATC clearances and instructions.
(a) When an ATC clearance has been obtained, no pilot in command may deviate from that clearance unless an amended clearance is obtained, an emergency exists, or the deviation is in response to a traffic alert and collision avoidance system resolution advisory. (Ed. Note: More follows but is irrelevant to this discussion.)

§ 91.185 IFR operations: Two-way radio communications failure.

(c) IFR conditions. If the failure occurs in IFR conditions, or if paragraph (b) of this section cannot be complied with, each pilot shall continue the flight according to the following:

(1) Route.

(i) By the route assigned in the last ATC clearance received;
(ii) If being radar vectored, by the direct route from the point of radio failure to the fix, route, or airway specified in the vector clearance;
(iii) In the absence of an assigned route, by the route that ATC has advised may be expected in a further clearance; or
(iv) In the absence of an assigned route or a route that ATC has advised may be expected in a further clearance, by the route filed in the flight plan.




I have examples of how to apply AVEF in my book, Radio Mastery for IFR Pilots available at

Your Question of the Week:

If you have ever departed IFR from an uncontrolled airport, ATC probably gave you a Clearance Void Time. The controller said to you, for example, “Void if not off by 10:15, time now 10:01 and one half. Basically, this meant ATC had approved your takeoff any time before the Clearance Void Time on 10:15 Zulu.

Here’s your question. What is a “Release Time” and how might ATC use it for your flight?

I’ll have the answer to that question, along with more topics to help you work with ATC while flying IFR, in the next edition of the IFR Flight Radio Show.


Full Route Clearances

“Cessna 9130 Delta, Ardmore Clearance, I have a full route clearance. Advise when ready to copy.”

Uh oh. A fire hose of information is about to come across the radio. Are you ready to take it all in and write it down?


I would argue, copying a full route IFR clearance is one of the hardest communication skills pilots face. The problem boils down to: Can you listen, comprehend and translate the clearance to paper at the same pace as the controller gives it to you? In this show, I’m going to reveal how to completely circumvent the problem and get your clearance copied correctly. I’ll show you how to do this no matter how complicated the clearance.

Show Resources

(FRC = Full Route Clearance)

J.O. 7110.65 Air Traffic Control (Manual)


e. When a filed route will require revisions, the controller responsible for initiating the clearance to the aircraft must either:

1. Issue a FRC/FRC until a fix; or

2. If it reduces verbiage, state the phrase: “Cleared to (destination) airport, or cleared NAVAID, intersection, or waypoint (type if known), (SID name and number and SID transition, as appropriate), then as filed, except …” Specify the necessary revision.


Your Filed Route

SZW        OTK

Your Cleared Route



clearedRouteSZW2 CEWrss

Your Filed Route

CEW     V241      RSS

Your Cleared Route


Clearance Magic: Copy IFR clearances with ease and accuracy every time.

Clearance Magic at

Your Question of the Week:

You are flying northeast on Victor Airway 17 between the San Antonio Vortac and the Centex Vortac. The controller at Houston Center says, “Cessna 30 Delta, turn right 20 degrees, vectors for traffic.” As you turn to the right, you read back, “Cessna 30 Delta, right 20 degrees.” The controller follows up with, “Cessna 30 Delta, expect direct . . .” And then the radio goes silent.

Since that next transmission was cut off, you say, “Cessna 30 Delta, say again.” There’s no response. In fact, you hear no other transmissions from the controller or from other aircraft.

You look at your radio control heads and notice the entire stack of radios and your transponder appears unpowered. You try contacting Houston Center again and not only do you not get reply, you can’t even hear a sidetone of your own voice as you transmit.

You run through every procedure you can think of to revive your radios but nothing works, and you do not have a portable battery operated radio on board to act as a backup. Without question, you are radio out, or NORDO if you prefer.

At this point, do you turn left to rejoin Victor 17 and continue along your previously cleared route of flight, or do you turn left and proceed from your present position direct to the Centex Vortac?

I’ll have the answer to that question, along with a full explanation in the next edition of the IFR Flight Radio Show.


Cleared for the Visual Approach, Or Not

  1. You are taking radar vectors to an ILS approach.
  2. The controller points out traffic you are following.
  3. You report the traffic in sight.
  4. ATC tells you to follow the traffic and clears you for a visual approach.
  5. Two minutes later, you lose sight of the traffic you were supposed to follow.
  6. Now what?!

Also in this week’s show:

We can talk all day about the correct way to use your call sign in a radio transmission. All that talk doesn’t add up to a hill of beans if pilots aren’t using their call sign at all when talking to ATC.

The answer to the Question of the Week asked in your last show, plus a brand new question to ponder.

Show Resources:

AIM 5−5−11. Visual Approach

b. Controller.

1. Do not clear an aircraft for a visual approach unless reported weather at the airport is ceiling at or above 1,000 feet and visibility is 3 miles or greater.

2. Issue visual approach clearance when the pilot reports sighting either the airport or a preceding aircraft which is to be followed.

3. Provide separation except when visual separation is being applied by the pilot.

4. Continue flight following and traffic in- formation until the aircraft has landed or has been instructed to change to advisory frequency.

5. Inform the pilot when the preceding aircraft is a heavy.

6. When weather is available for the destination airport, do not initiate a vector for a visual approach unless the reported ceiling at the airport is 500 feet or more above the MVA and visibility is 3 miles or more. If vectoring weather minima are not available but weather at the airport is ceiling at or above 1,000 feet and visibility of 3 miles or greater, visual approaches may still be conducted.

a. Pilot.

5. Advise ATC immediately if the pilot is unable to continue following the preceding aircraft, cannot remain clear of clouds, needs to climb, or loses sight of the airport.

I have a complete discussion about why using your call sign in every transmission to ATC is absolutely critical. Check out the first 10 minutes of the Radar Contact Show episode “We’d Be Thrilled if You Simply Used Your Call Sign!”

Your Question of the Week:

You are on a long, wide base leg, taking radar vectors to an ILS approach. The approach controller asks you if you have the airport in sight. You do have the airport in sight but due to hazy visibility you don’t see the landing runway.

You know if you report the airport in sight, the controller is probably going to clear you for the visual approach. Due to your lack of orientation to the runway, you would prefer to continue with radar vectors to intercept the ILS.

Do you have the option to continue with vectors to the ILS approach even if you have the airport in sight? If so, what would you say to the approach controller?

I’ll have the answers to those questions, along with a full explanation, in your next edition of the IFR Flight Radio Show.

If you are in the process of researching a new radio headset, check out my Headset Buyer’s Guide at


Enroute ATC: How to Request Direct to a Point

Cutting a corner by requesting direct to a point further along your route of flight could save time and fuel. An enroute air traffic controller will try to honor your request if circumstances permit. First and foremost it pays to know how to make a request direct to a point. We’ll discuss all the particulars of requesting direct in this edition of the IFR Flight Radio Show.


Show Resources:

AIM 4−4−4. Amended Clearances

c. Pilots have the privilege of requesting a different clearance from that which has been issued by ATC if they feel that they have information which would make another course of action more practicable or if aircraft equipment limitations or company procedures forbid compliance with the clearance issued.

AIM 5−1−8. Flight Plan (FAA Form 7233−1)− Domestic IFR Flights

c. Direct Flights

4. Increasing use of self-contained airborne navigational systems which do not rely on the VOR/VORTAC/TACAN system has resulted in pilot requests for direct routes which exceed NAVAID service volume limits. These direct route requests will be approved only in a radar environment, with approval based on pilot responsibility for navigation on the authorized direct route.

J.O. 7110.65V Air Traffic Control**

3. Issue a clearance “direct” to a point on the previously issued route.
CLEARED DIRECT (fix,waypoint).

Clearances authorizing “direct” to a point on a previously issued route do not require the phrase “rest of route unchanged.” However, it must be understood where the previously cleared route is resumed. When necessary, “rest of route unchanged” may be used to clarify routing.

**(The reference manual for air traffic controllers. Pilots are not required to know the contents of this manual.)

Check out the Headset Buyer’s Guide at for help choosing an aviation radio headset.

Your Question of the Week:

You are flying at your filed cruise altitude on a Victor Airway 159 inbound to the Ocala Vortac in North Central Florida. After crossing over the top of Ocala, your cleared route of flight has you making a 46-degree turn to the right to continue on Victor 441 to the Gainesville VORTAC*. With 30 miles to go to the Ocala VORTAC, you decide you’d like to save time and fuel by proceeding direct Gainesville.

Checking your enroute chart (see the chart segment above), given your present position, even if you cut the corner and proceed direct right now, your new route of flight will keep you well clear of the Palatka MOAs northeast of your position.

You get on the radio and say to Jacksonville Center, “Skyhawk 30 Delta requests direct Gainesville*.” The controller replies, “Skyhawk 30 Delta, I have your request.”

Four minutes pass. The controller has said nothing further to you about your request to proceed direct Gainesville*. Instead, he says, “Skyhawk 30 Delta, contact Jacksonville Center on 127.8.” Here are your questions.

First, why do you think the controller never approved your request? Second, will you have to make the same request of your next controller, or will he have your request in his todo list when you check in.

I’ll have the answers along with complete explanations in your next show.


In this week’s question, I incorrectly identify the Gators VORTAC as the Gainesville VORTAC. I graduated from the University of Florida at Gainesville, so one of two things is true. Either my education was inadequate, or I recalled the name of the VORTAC as it was _____ years ago when I attended college.


Enroute ATC: Traffic and Radar Handoffs

If your IFR training was like mine, you spent a lot of time taking radar vectors to instrument approaches using approach control service. Less time was spent working with enroute center controllers.


Communicating with an enroute controller at an air route traffic control center (ARTCC) is its own special skill. In today’s show, we’ll look at ARTCC communication during traffic avoidance vectors and during radar handoffs.

Show Notes and Resources:

AIM 5−3−1. ARTCC Communications

2. An ARTCC is divided into sectors. Each sector is handled by one or a team of controllers and has its own sector discrete frequency. As a flight progresses from one sector to another, the pilot is requested to change to the appropriate sector discrete frequency.

Notice how the following statement in the AIM has no requirement to repeat the numbers of an assigned radio frequency.

AIM 4−2−3. Contact Procedures

d. Acknowledgement of Frequency Changes.

1. When advised by ATC to change frequencies, acknowledge the instruction. If you select the new frequency without an acknowledgement, the controller’s workload is increased because there is no way of knowing whether you received the instruction or have had radio communications failure.

More info about: Radio Mastery for IFR Pilots Everything you need to know to talk to Air Traffic Control while flying IFR

Trying to decide which radio headset to buy? Check out my Headset Buyer’s Guide at


Hanging On to ATC Clearances

How good are you at hanging on to an ATC clearance that is long and complicated?

Houston Center says, “Commanche 448 Juliette Mike, reduce speed to 160, then descend and maintain 9,000 thousand. The Galveston altimeter is 29.86.”

In this week’s edition of IFR Flight Radio, I’ll give you tips and techniques for recording and reading back a long, complicated ATC clearance.

Add-On Instrument Bugs

Add-On Instrument Bugs

We’ll consider the answer to the Question of Week presented in our last show.

I’ll also have a brand new Question of the Week for you to chew on.

Pull the chocks and get ready to taxi. IFR Flight Radio’s is on the move again.

Supplements and References for this week’s show:

Short Term Memory References

Add-On Aircraft Instrument Bugs

At Sporty’s Pilot Shop

At Aircraft Spruce and Specialty

AIM 5-4-1 2. “DESCEND VIA.”

(a) Clearance to “descend via” authorizes pilots to:

(1) Vertically and laterally navigate on a STAR/RNAV STAR/FMSP.

(2) When cleared to a waypoint depicted on a STAR/RNAV STAR/FMSP, to descend from a previously assigned altitude at pilot’s discretion to the altitude depicted for that waypoint, and once established on the depicted arrival, to navigate laterally and vertically to meet all published restrictions.


What You are Required to Read Back to ATC

Do you know what you are required to read back when ATC issues a clearance to you? Apparently a lot of pilots–including high-time pros–don’t know what they are required to read back.


A contact of mine at Chicago Approach Control said he is pulling his hair out because many pilots do not read back his clearances as expected. He asked me if there are any regs to control what and how a pilot reads back an ATC clearance. Here’s my answer to him in the very first episode of the IFR Flight Radio Show.

Supporting Notes for this Show:

Questions? Write to me at

Or add a comment below the notes for this show.

Or follow me at

91.123 Compliance with ATC clearances and instructions.

(a) When an ATC clearance has been obtained, no pilot in command may deviate from that clearance unless an amended clearance is obtained, an emergency exists, or the deviation is in response to a traffic alert and collision avoidance system resolution advisory. However, except in Class A airspace, a pilot may cancel an IFR flight plan if the operation is being conducted in VFR weather conditions. When a pilot is uncertain of an ATC clearance, that pilot shall immediately request clarification from ATC.

(b) Except in an emergency, no person may operate an aircraft contrary to an ATC instruction in an area in which air traffic control is exercised.

(c) Each pilot in command who, in an emergency, or in response to a traffic alert and collision avoidance system resolution advisory, deviates from an ATC clearance or instruction shall notify ATC of that deviation as soon as possible.

(d) Each pilot in command who (though not deviating from a rule of this subpart) is given priority by ATC in an emergency, shall submit a detailed report of that emergency within 48 hours to the manager of that ATC facility, if requested by ATC.

(e) Unless otherwise authorized by ATC, no person operating an aircraft may operate that aircraft according to any clearance or instruction that has been issued to the pilot of another aircraft for radar air traffic control purposes.

AIM 4−4−7. Pilot Responsibility upon Clearance Issuance

b. ATC Clearance/Instruction Readback.

Pilots of airborne aircraft should read back those parts of ATC clearances and instructions containing altitude assignments, vectors, or runway assignments as a means of mutual verification. The read back of the “numbers” serves as a double check between pilots and controllers and reduces the kinds of communications errors that occur when a number is either “misheard” or is incorrect.

My New Book:

Radio Mastery for IFR Pilots. Available now at *

Your Question of the Week:

You are inbound to an airport with a published Standard Terminal Arrival called the Candy Five. As you approach the VORTAC the defines the beginning of the arrival, the controller at Chicago Center says, “Twin Cessna 553 UM, proceed via the Candy 5. Descend and maintain 9,000.” You readback this clearance and navigate along the route for the Candy 5. You also begin a descent to 9,000. Then you notice, 20 miles ahead there is an intersection with a published crossing restriction of 8,000 feet. Would you descend to cross that intersection at 8,000?

*I receive a small commission when you use this link to make a purchase at


The Book Lives!

Radio Mastery for IFR Pilots

“Everything you need to know to talk to Air Traffic Control while flying IFR.”
You know how long it takes to write a book that makes that claim? A year and a half. How long did I think it would take? Oh, only about 6 months.

I missed my deadline by 1 year. In geological time that’s a blink of an eye.

It was worth it though. In that time, I got some great help from pilots, certified flight instructors, and certified professional controllers. Even the FAA chimed in on one topic.

The result is:

  • A very readable book filled with easy this-is-how-to-do-it
  • Sprinkled with (my idea of) humor
  • That will make you a pro communicator on the radio.

Radio Mastery for IFR Pilots is available right now at*

Update for Oct 31: The “Search Inside this Book” feature has been added to the listing at The listing for the book at just went online today (Oct 26). They have yet to add the full “Search Inside this Book” feature to the listing. If you would like a peak inside portions of the book that aren’t shown at, you can do it right here.

*The fine print: I earn a commission from when you use this link to order.


Top 5 Time-Wasting Phrases Pilots Use

Is your radio vocabulary littered with garbage?

Is your radio vocabulary littered with garbage?

“And Oakland Center, Beach Ball 373GK, 17,000.”

5.”And” is one of those filler sounds, similar to “Uh” and “Um” that sprinkles some pilots’ vocabularies. It’s a lousy habit. The only cure is to become conscious of it and cut it out.


“Cleveland Center, Serious 749NE, with you, at Flight Level 330.”

4.”With you.” Really?! Where else would this pilot be? Floating on the fifth plain of consciousness, phoning it in by mental telepathy? You hear this extraneous phrase so often from pilots you’d swear it was in the AIM’s Pilot/Controller Glossary.


ATC: “Twin Chessnut 36W, say your heading.”

Pilot: “Twin Chessnut 36W heading 185 at this time.”

3. “At this time.” Huh. I could have sworn the air traffic controller asked the pilot to say his heading. He must have thought the controller asked him what he thought his heading will be further along the space-time continuum.


“Norcal Approach, Pied Piper 802VX with a request.”

2. “With a request.” Oh, I’m sorry. Didn’t the pilot think his controller was listening to his frequency? After all, that’s a controller’s job. What’s that? You think he was just trying to be courteous? You know what would be courteous? If he quit tying up the radio with an extra radio transmission and just made his request.

Seriously, I’ve asked several controllers what they think about pilots saying, “With a request.” Most don’t care for it. They consider it a poke in the ribs that they don’t need. They all told me, if you have a request, make it without an introduction.

One Exception

There’s one exception to the no-introduction-necessary school of thought. If you have complicated request, tell your controller about what you are going to request. For example, if you have a long and complex route change request, it would pay to say, “Pied Pier 802VX with a route change request.” This gives the controller time to grab a pen. He’ll also select a reasonable break in his routine let you state your extensive request. It’s similar to Clearance Delivery saying, “I have your clearance. Advise when ready to copy.”

Note the difference between this and a generic wake-up call. Stating the nature of your request has substance that helps the controller prepare. Simply saying, “With a request” is uninformative, unnecessary, and maybe a little insulting.


ATC: “Falcone 5TY, say your airspeed.”

Pilot: “Falcone 5TY, 210 knots. Whatta ya need?”

ATC: “I needed you to say your airspeed, which you did, so thank you.”

1. “Whatta ya need?” No kidding, the conversation above represents an actual radio exchange I heard recently. I know, and most air traffic controllers know, a pilot who says, “Whatta ya need?” is trying to sound cooperative. Controllers already know pilots will cooperate with them.

The real problem with “Whatta ya need?” is it forces the controller to reply. In most cases, when a controller asks a pilot about his speed, it’s to help the controller plan his spacing between aircraft. The controller needs a moment to think, not reply.

The Takeaway

I’m not trying to sound like a grumpy old pilot. “Hey you brats! Get off my lawn or I’ll call the cops!” The point of this exercise is to get you thinking about streamlining your transmissions. There are words and phrases that have crept into the pilot vocabulary which take up time on the radio and accomplish nothing.


Take a moment to analyze your own repertoire of responses to ATC. Is there anything you say that is fluff? If so, I recommend cutting those time-wasting phrases off at the knees. If you recognize that an aviation frequency is a time-share commodity, then make a conscious effort to be efficient on the radio.


Yes, You’re IFR, But Keep Clearing for Traffic

Yes, I know you’re IFR.

Yes, I know ATC has you covered with traffic advisories and alerts.

Yes, I know you have TCAS or ADS-B In.

It wasn't nearly this close, but it still got our attention. (stock photo.)

It wasn’t nearly this close, but it still got our attention.
(stock photo.)

When you’re in VMC, keep clearing for traffic. You wouldn’t believe what can pop up as unannounced traffic, in the most unexpected place. I wrote about a surprise encounter with a VFR aircraft at

P.S. When ATC says, “Turn right immediately,” turn right immediately.