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I know it means “I have understood the instruction and will comply.” However, any instruction that

  • is a clearance,
  • concerns runway use or
  • contains altitude/level, heading, speed or squawk code

should be read back. And that seems to cover most instructions.

So what is an instruction, but does not require a read-back and may be instead answered by just ‘wilco’ (+ callsign)?

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  • $\begingroup$ Allowable use of wilco will vary by jurisdiction. $\endgroup$ – J Walters Nov 25 '16 at 1:27
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When instructed to report something.

ATC: Cimber 626 turn left heading 120, cleared ILS approach runway 09, report established

Pilot: Heading left 120, cleared ILS approach runway 09, WILCO, Cimber 626


ATC: OYABC airborne time 33, report passing Dalhem

Pilot; (Roger), WILCO, OYABC


ATC: Lufthansa 135, traffic is a Boeing 737 on 5 miles final for runway 09, report in sight

Pilot: WILCO, Lufthansa 135

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  • $\begingroup$ The only one of these that I would use is the last one. On the first one, you’ve already read back the required parts of the instruction and Wilco just confuses things. On the second one, you don't need both Roger and WIlco. however, unless I was in really busy airspace, I would read back the reporting point. $\endgroup$ – JScarry Nov 24 '16 at 18:48
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    $\begingroup$ @JScarry The example I've used are in compliance with the ICAO Manual of Radiotelephony (Doc 9432). I'm not saying this is exactly how pilots are doing it - but it's how they should be doing it. $\endgroup$ – J. Hougaard Nov 24 '16 at 18:53
  • $\begingroup$ Off the top of my head, the only times that I use 'wilco' are when I'm issued 'report established' or 'report airport in sight'. I don't even think @JHougaard's example of 'report passing Dalhem' is appropriate. If a fix is included in the instruction, you need to repeat the name of the fix. Even if that's not required by regs, I'm repeating it so that I know that I got the name of the fix correct. I think it's better to be absolutely clear that you're on the same page, even if the mic is keyed for 2 seconds longer. $\endgroup$ – Dustin Aug 16 '17 at 22:46
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According to the Pilot Controller Glossary:

WILCO− I have received your message, understand it, and will comply with it.

ROGER− I have received all of your last transmission. It should not be used to answer a question requiring a yes or a no answer.

If you are a general aviation pilot, ATC wants to be sure that you have understood the instruction that you have been given and will expeditiously comply with it. If you are given a heading for traffic, altitude, clearance to land, hold short instruction, or clearance into Class B airspace, you should always repeat it back. I would not mix and match Roger and Wilco in readbacks.

Some examples:

At my home airport when given a taxi instruction:

Tower: 90J Taxi to parking via Echo, Juliet, Mike. Remain this frequency.

I could reply Wilco, and my abbreviated callsign. e.g.

Wilco, 90J

At an unfamiliar airport, unless the taxi instructions were very simple, I’d read them back.

When ATC can immediately see that I have complied with the instruction and it is fairly lengthy, I could use Wilco.

Tower: 90J Make a 360 to the right for spacing, watch for birds on final, follow the Cessna on left base.

Tower: 90J Extend your downwind. I’ll call your base.

On the other hand, if it involves a safety of flight issue, I’ll read back what I am going to do.

Tower: 90J Follow the Cessna entering left base.

90J: Looking for the Cessna 90J.

I don’t know that I have ever used Roger. It is usually simpler to just repeat the information or respond with what you are going to do.

ATC: 90J traffic 12 o'clock 7 miles north bound 3,500'

I could respond with Roger, but I want them to know that I ether have the traffic in sight or that I am looking for it. So I would respond with either "Traffic in sight" or "Looking".

ATC: 90J Santa Barbara altimeter 29.92

I suppose you could respond with Roger, but repeating the setting is the preferred response.

I have heard the tower and flight following use Roger—although it’s often “Roger that”.

I am in the practice area and then let ATC know that I am going to fly somewhere else.

Examples:

When I’m starting my VFR descent to the airport.

Reporting birds near the airport.

If you listen to Live ATC, you will hear airline pilots use Wilco in busy airspace, but in my experience as a general aviation pilot, it is quite rare.

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    $\begingroup$ As a controller, I would very much like to stress that you should not use Wilco in lieu of a readback when a readback is required. Taxi instructions or instructions to fly a certain procedures (e.g. a 360) must absolutely be read back. Every rule book says so. This applies even on a busy frequency. We will not issue instructions to you unless we have time to listen to the readback. Replying with Wilco will only add doubt as to whether you have actually understood the instructions given, and could easily result in extra workload for the controller. $\endgroup$ – J. Hougaard Nov 24 '16 at 20:01
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    $\begingroup$ @JHougaard In my experience, the only taxi instructions that controllers insist on hearing read back are 'hold short of runway XX'. And that is relatively recent, maybe 5 years or so.. I’ve been re-reading the AIM and in 4−3−18. Taxiing it states “1. Good operating practice dictates that pilots acknowledge all runway crossing, hold short, or takeoff clearances unless there is some misunderstanding, at which time the pilot should query the controller until the clearance is understood.” It does not explicitly state that you must read back the taxi instruction. Do you have another reference? $\endgroup$ – JScarry Nov 24 '16 at 21:23
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    $\begingroup$ @JScarry J. Hougaard is a controller in Europe; standards are often slightly different there. $\endgroup$ – Pondlife Nov 24 '16 at 22:47
  • $\begingroup$ In some situations I'll acknowledge a controller by just replying my callsign, like when they are telling me that new weather information is available. Obviously this is VFR only. At some extremely busy airports/times we also reply just by keying our mic. $\endgroup$ – Ron Beyer Nov 25 '16 at 2:28
  • $\begingroup$ Replying 'wilco' for taxiway instructions sounds like a great way to frustrate a ground controller at a busy airport with lots of active taxiways. Off the top of my head, the only times that I use 'wilco' are when I'm issued 'report established' or 'report airport in sight'. I don't even think @JHougaard's example of 'report passing Dalhem' is appropriate. If a fix is included in the instruction, you need to repeat the name of the fix. $\endgroup$ – Dustin Aug 16 '17 at 22:43

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