Difference between clearance and instruction?

[yrp]

I've always been a bit unclear on the practical difference. Figuring out when it is an instruction vs clearance is straightforward. If ATS says "clears", "cleared" or similar, it is a clearance. An instruction has a verb in the imperative mood.

But for a pilot, they amount to the same thing, don't they? You have to follow both clearances and instructions unless unable for some reason, in which case (for both) you inform ATC.

Is the difference just who initiates the request - ie for a clearance, ATC is approving a pilot's request whereas for an instruction ATC initiates it? If so, once issued, what difference does it make to the pilot? Is it that with a clearance, you (the pilot) can request a change (if a different route/alt/change of dest is preferred for example) but you wouldn't for an instruction unless unable to comply?

[invertedattitude]

I try to only use the word "cleared" for route clearences, we do it every day giving Oceanic clearences, I know some people use "cleared" for a climb or descent, which some pilots often interpret as pilots discretion.

An instruction for an altitude change should be issued as an instruction, especially for foreign pilots if you expect them to start moving in that direction now.

Any pilots reading this, a small somewhat related note, if ATC says "soandso123, descend flight level 290"

Please don't come back with "Ok, 290 is that pilots discretion?"

If it's PD we'll tell you.

Also if you request descent and you're given descent, vacate your altitude now, not in 15-20 miles.


I think from a pilots view there shouldn't be much difference, if ATC says "Cleared to toronto via, YSO, WASIE2" It's not as if you can then make your own route anyway.

[CCR]

Have to disagree with you inverted. Many times I have asked if it was PD when my TOD was still ahead of me by a distance and was told "yes" it is. I'm only asking when it does not make sense and the controller hasn't provided me with any other info. If you are stepping me down early for traffic let me know and I won't ask...

As far as direct clearances, (i.e. YHZ direct BUF) I know it seems to be the norm, but we have been told by our higher ups to only accept a direct clearance if it's in the first or last 200nm or it makes absolute no difference to track line. Otherwise we are to turn it down or talk to DXP first. Too many guys not thinking and were turning into wind to achieve a shorter distance but ultimately a higher fuel burn.So, if you are giving guys a direct without them asking for it, you may have a pause before they answer and they may ask if it is for ATC reasons because otherwise the answer is no. You can help negate this pause by giving us the reason, if there is one, prior to issuing the clearance.

[Pygmie]

The basic difference between a clearance and an instruction is that an instruction must be followed unless safety will be compromised, whereas a clearance can be turned down by the pilot for other reasons.

For example, if an instruction such as "fly heading 310" is issued, unless that heading will put the aircraft into a CB or something similar the pilot must comply with it.

On the other hand, if a clearance such as "cleared direct YYZ, flight planned route" is issued, the pilot can choose not to accept the clearance.

[C-GGGQ]

Bingo

[thatdaveguy]

The basic difference between a clearance and an instruction is that an instruction must be followed unless safety will be compromised, whereas a clearance can be turned down by the pilot for other reasons.

For example, if an instruction such as "fly heading 310" is issued, unless that heading will put the aircraft into a CB or something similar the pilot must comply with it.

On the other hand, if a clearance such as "cleared direct YYZ, flight planned route" is issued, the pilot can choose not to accept the clearance.

ATC instructions must be complied with subject to the PIC's final judgement if safety is endangered
ATC Clearances must be complied with if accepted subject to the PIC's final judgement if safety is endangered

[yrp]

On the other hand, if a clearance such as "cleared direct YYZ, flight planned route" is issued, the pilot can choose not to accept the clearance.

ATC instructions must be complied with subject to the PIC's final judgement if safety is endangered
ATC Clearances must be complied with if accepted subject to the PIC's final judgement if safety is endangered

Thanks guys. Now that I look closer, I found it in the the TC-AIM (RAC 1.7) and FTGU. It's the "if accepted" part which I'd missed.

[invertedattitude]

Regarding directs, we see some pretty wonky routes do to upper winds.

If I'm not busy, I'll sometimes ask a pilot if he would like direct XXX, 8/10 it's a yes, but sometimes it's a no for various different reasons.

Also there's many times, where a direct will fix a traffic problem without having to move airplanes out of their flight levels, in this case I'll tell an aircraft "Proceed direct" instead of cleared. That being said if the pilot comes back and says "We'd like to stay on route" it's at that point I'll move that airplane into another flight level.

If I'm not busy I'll throw out some options if there are some that work for me as well.


Anyway I'm blabbering now, long story short if a controller needs something done now it will be issued as an instruction.

Have to disagree with you inverted. Many times I have asked if it was PD when my TOD was still ahead of me by a distance and was told "yes" it is.

Indeed theres been times when a pilot has asked me, and I will say yes if it fits my plan, my only point is that sometimes we need you to start down now. Normally I'll include something like "to accomodate your arrival" or "for traffic" to avoid such questions.

Just keep in mind there's no requirement for a controller to advise you of why he's descending you, challenging a controllers decision to descend you could end you up in hot water if separation could/would have been affected.

[CCR]

If me asking a question causes a seperation loss, there was a problem from your side a long time before you asked me to descend...no?

[FamilyGuy]

If me asking a question causes a seperation loss, there was a problem from your side a long time before you asked me to descend...no?

Agreed - I think there is a phrase for that..."no shite sherlock" or similar.

Pilots can not accept an instruction as well - just better make sure it's for a REALLY good reason.

If need be ATC can also say "ATC instructs CGXXX to descend NOW". Kinda gets the seriousness across now don't it.

[invertedattitude]

If me asking a question causes a seperation loss, there was a problem from your side a long time before you asked me to descend...no?

You're thinking a little too on the short term.

If I have an airplane crossing your descent path at FL320, you will cross in 4-5 minutes, you are at say FL350 my initial plan is to wait until the "normal" area you would ask for descent, and thus pass you overtop of that airplane before issuing your descent.

However you request descent earlier than most, I can get you down through that aircrafts level safely if you vacate now so I issue your descent, but if you plan to wait 15-20 miles for the TOD on your FMS, now that messes up my new plan for you, rather than if you had vacated your flight level immediately, it may now require a vector for you or the other aircraft, or levelling you off, which as we all know pilots don't normally like to do.

Those numbers are just random to try and paint a picture but you see my point?

As family guy said however, giving the instructions in the imperitive mood definately helps.

"Soandso Requesting descent"

"Roger, descend NOW FLxxx"

Long story short here, if a controller says "Now" anywhere in a transmission, I wouldn't recommend coming back and asking if it's PD. I can't vouch for every controller out there, but in my case I will always issue descents at PD well ahead of time when able, but generally if I give you descent and I don't say PD, 95% of the time I want you to vacate the altitude now.