Effect of Density Altitude on Crosswinds

[vintage cessna]

While it is true that flying uncoordinated by more than a few degrees is unlikely, having a non-slaved DG drift off, or the compass calibration being off, is quite common, and will cause ATC frustration as they try to vector you.
The point again is that when ATC gives you a vector, they expect that to become your flight path though the airmass you are in, which normally should be the direction of your nose relative to magnetic North at your location, in coordinated flight. Any significant deviation from that will cause confusion.

If ATC were to assign you a heading, that wouldn't "normaly " be the direction of your nose relative to magnetic North, that would always be the case. For what ever vector ATC gives you, they are expecting it to produce a certain track over the ground since that is their only reference. If they assign you a heading and don't see the track they want, there is no confusion, they just assign you another heading. Quite often ATC is not sure what the wind is doing to your aircraft so will assign turns specifying that you turn a certain number of degrees left or right. For example if they told you to turn 30 degrees to the left, the comtroller is going to expect to see your track change by 30 degrees. You should be able to comply with that even if your DG is off. The only way for you to comply is to move your nose around 30 degrees to the left.

 

[RotorDude]

If ATC were to assign you a heading, that wouldn't "normaly " be the direction of your nose relative to magnetic North, that would always be the case. For what ever vector ATC gives you, they are expecting it to produce a certain track over the ground since that is their only reference. If they assign you a heading and don't see the track they want, there is no confusion, they just assign you another heading. Quite often ATC is not sure what the wind is doing to your aircraft so will assign turns specifying that you turn a certain number of degrees left or right. For example if they told you to turn 30 degrees to the left, the comtroller is going to expect to see your track change by 30 degrees. You should be able to comply with that even if your DG is off. The only way for you to comply is to move your nose around 30 degrees to the left.

That's true, if they give you a relative heading, "turn 30 degrees left", you should just do that, regardless of how far off you are.
And you are right that in general, they don't know exactly what the wind is doing to you, and just try to work around that.
But a typical problem is when they give you a heading, say 090, and then after a few minutes you discover (with a non-slaved compass) that your DG has drifted off, say by 10 degrees. If you then correct the DG to match the compass, and continue on the assigned heading, you'll end up turning 10 degrees, which will definitely annoy ATC.
So when flying in the ATC environment, you should try your best to always keep your heading as close as possible to what ATC expects, which means frequent DG/compass checks, if applicable.

 

[vintage cessna]

The point again is that when ATC gives you a vector, they expect that to become your flight path though the airmass you are in, which normally should be the direction of your nose relative to magnetic North at your location, in coordinated flight. .

When you make statements like like this, I, for one, am not sure what you are thinking. Like "normally should be". That implies there are exceptions, but there are no exceptions I know of.

Then you say "airmass you are in", as if the properties of various airmass' would make a difference. Maybe you actually understand things better than I think you do, but it is impossible to tell.

 

[RotorDude]

When you make statements like like this, I, for one, am not sure what you are thinking. Like "normally should be". That implies there are exceptions, but there are no exceptions I know of.

Then you say "airmass you are in", as if the properties of various airmass' would make a difference. Maybe you actually understand things better than I think you do, but it is impossible to tell.

"Normally should be" means that they allow some tolerance for small errors.
"Airmass you are in" means that they take into consideration that even though you are moving (say) due North through your airmass, if there is a 30kt westerly wind at your altitude, they'll expect you to track right by X degrees, depending your airspeed. In addition to wind (technically flow rate of your airmass), pressure and temperature of your airmass would affect your TAS vs. IAS, or Mach speed for the flight levels.

 

[vintage cessna]

"Airmass you are in" means that they take into consideration that even though you are moving (say) due North through your airmass,

Here again is a statement that will have people scratching their heads. You use the word "moving" instead of "heading". They have completely different connotations. What ever occupation or activity you are engaged in, the people engaged in that activity all have to use the same accepted definitions or no will know WTF anyone means.

 

[RoscoeT]

Holy hell. This thread proves there is infinite potential in attempting to spin simple and accurate statements into proof that those statements make you a moron.

 

[dtuuri]

This thread proves there is infinite potential in attempting to spin simple and accurate statements into proof that those statements make you a moron.

Why does everything look like a spin to you?

dtuuri

 

[RoscoeT]

Why does everything look like a spin to you?

dtuuri

Done too many I guess, and now have the "wobblies".

 

[RotorDude]

"Airmass you are in" means that they take into consideration that even though you are moving (say) due North through your airmass

Here again is a statement that will have people scratching their heads. You use the word "moving" instead of "heading". They have completely different connotations. What ever occupation or activity you are engaged in, the people engaged in that activity all have to use the same accepted definitions or no will know WTF anyone means.

Actually the difference between the "heading" you read on your DG and the path/direction your aircraft is moving through its airmass is what this issue is about. If you are always in coordinated flight, your DG is always matched to your compass, and your compass is correctly calibrated, there would be no difference, and when ATC tell you to head to 090 they would be able to predict where you'll turn (i.e. your ground track on their scope) based on the winds at your altitude and your airspeed.

 

[vintage cessna]

Actually the difference between the "heading" you read on your DG and the path/direction your aircraft is moving through its airmass is what this issue is about. If you are always in coordinated flight, your DG is always matched to your compass, and your compass is correctly calibrated, there would be no difference, and when ATC tell you to head to 090 they would be able to predict where you'll turn (i.e. your ground track on their scope) based on the winds at your altitude and your airspeed.

See , you describe the issue as "path through its' airmass" . If we are talking about ATC here, the issue is your track over the ground. That is the only thing they know about your "path" .

I'm not trying to split hairs here, you just phrase things in ways I'm not familiar with. First time I went to England, a guy asked me if I had a "fag" . I totally misconstrued what he meant also.

 

[RotorDude]

See , you describe the issue as "path through its' airmass" . If we are talking about ATC here, the issue is your track over the ground. That is the only thing they know about your "path" .

I'm not trying to split hairs here, you just phrase things in ways I'm not familiar with. First time I went to England, a guy asked me if I had a "fag" . I totally misconstrued what he meant also.

Well, if you have another term to describe the direction (relative to magnetic north) of your aircraft's actual path through its airmass, tell us what it is.
Remember this cannot be your "indicated heading", as indicated on the DG, since that could be off, depending on compass calibration, DG drift, and slip/yaw attitude.

 

[vintage cessna]

Well, if you have another term to describe the direction (relative to magnetic north) of your aircraft's actual path through its airmass, tell us what it is.
Remember this cannot be your "indicated heading", as indicated on the DG, since that could be off, depending on compass calibration, DG drift, and slip/yaw attitude.

How about "track" or "course". All pilots and air traffic controllers should have the same understanding of those words.

 

[RotorDude]

How about "track" or "course". All pilots and air traffic controllers should have the same understanding of those words.

No, both "track" and "course" refer to path over the ground, not in the air (those could be 30 degrees off with a good crosswind). When ATC tells you to head 090, they don't mean you should track that way, or go on that course.

 

[vintage cessna]

No, both "track" and "course" refer to path over the ground, not in the air (those could be 30 degrees off with a good crosswind). When ATC tells you to head 090, they don't mean you should track that way, or go on that course.

I know, and ATC will know that your "heading" may differ from your course. When ATC says "fly heading 090" they just want you to point the nose to 090. They are just trying to place you on a desired course which may or may not match your heading. You keep talking about movement through an airmass. ATC's only reference for your movement is the ground, that is one reason why definitions of heading , track and course have been established in aviation.

 

[RotorDude]

I know, and ATC will know that your "heading" may differ from your course. When ATC says "fly heading 090" they just want you to point the nose to 090. They are just trying to place you on a desired course which may or may not match your heading. You keep talking about movement through an airmass. ATC's only reference for your movement is the ground, that is one reason why definitions of heading , track and course have been established in aviation.

Yes, ATC is aware that your path through your airmass (loosely your "heading") is different from your ground track, but they try to compensate for it when they issue vectors.
They expect your "heading" to be (roughly) aligned with your path through the airmass you fly in. As example, if you have uncorrected DG drift or a big compass calibration error, that may mess with their expectations, and can annoy them, esp. if you suddenly discover and correct the DG drift while on a vector (as I noted above).

 

[vintage cessna]

Yes, ATC is aware that your path through your airmass (loosely your "heading") is different from your ground track, but they try to compensate for it when they issue vectors.
They expect your "heading" to be (roughly) aligned with your path through the airmass you fly in. As example, if you have uncorrected DG drift or a big compass calibration error, that may mess with their expectations, and can annoy them, esp. if you suddenly discover and correct the DG drift while on a vector (as I noted above).

Last post, I have to go. But again, I'm not sure what you are trying to convey. ATC doesn't think in terms of "path through an airmass" . And why do say "loosely your heading" ?

 

[MAKG1]

Last post, I have to go. But again, I'm not sure what you are trying to convey. ATC doesn't think in terms of "path through an airmass" . And why do say "loosely your heading" ?

That has me scratching my head, too.

Your heading (and airspeed and climb rate) IS your path through the airmass, precisely. Your DG only reads your heading if you are coordinated. Your compass only reads your heading if you are coordinated, straight, level, and unaccelerated (plus a few weird corner cases like speeding up while exactly northbound).

When ATC tells you to follow a heading, that's what they mean. For avoiding other aircraft, they are all affected by the same wind. Sometimes ATC gets it wrong; I've been in high crosswinds double those forecast, in Class B at 3500, before. Then they will correct the instruction if needed.

 

[RotorDude]

That has me scratching my head, too.

Your heading (and airspeed and climb rate) IS your path through the airmass, precisely. Your DG only reads your heading if you are coordinated. Your compass only reads your heading if you are coordinated, straight, level, and unaccelerated (plus a few weird corner cases like speeding up while exactly northbound).

When ATC tells you to follow a heading, that's what they mean. For avoiding other aircraft, they are all affected by the same wind. Sometimes ATC gets it wrong; I've been in high crosswinds double those forecast, in Class B at 3500, before. Then they will correct the instruction if needed.

Yes, and since your DG may not be slaved, it may drift over time, between manual corrections. That could introduce a significant difference between the heading ATC expects from you and the one on your DG.

 

[RotorDude]

Last post, I have to go. But again, I'm not sure what you are trying to convey. ATC doesn't think in terms of "path through an airmass" . And why do say "loosely your heading" ?

I explained the reasons for "loosely" in the same message (and others).

 

[MAKG1]

Yes, and since your DG may not be slaved, it may drift over time, between manual corrections. That could introduce a significant difference between the heading ATC expects from you and the one on your DG.

If you have an unslaved DG, that's true. However, quite a number of aircraft (i.e., glass panels, remote compasses, INS's, etc.) have automatically adjusted DGs.

"Significant" to ATC seems to be 5 deg. If you've let your heading get that far off, you've screwed up. My adjustments are generally just a few degrees.

The point is your DG is not your heading. It is an estimate of your heading subject to a number of errors. Your heading is your path through the airmass.

 

[RotorDude]

Sure. And rather than a lot of mental gymnastics (like this thread), they'll often instruct "turn 20* left" or something like that to get their product (separation).

Yes, if they tell you "turn 20 degrees left", you should do just that, based on your current DG reading.
But if they tell you "turn left to a heading of 090", you should first double check your DG matches your magnetic compass, assuming non-slaved.

 

[RotorDude]

If you have an unslaved DG, that's true. However, quite a number of aircraft (i.e., glass panels, remote compasses, INS's, etc.) have automatically adjusted DGs.

"Significant" to ATC seems to be 5 deg. If you've let your heading get that far off, you've screwed up. My adjustments are generally just a few degrees.

The point is your DG is not your heading. It is an estimate of your heading subject to a number of errors. Your heading is your path through the airmass.

We are in full agreement.

 

[vintage cessna]

If you have an unslaved DG, that's true. However, quite a number of aircraft (i.e., glass panels, remote compasses, INS's, etc.) have automatically adjusted DGs.

"Significant" to ATC seems to be 5 deg. If you've let your heading get that far off, you've screwed up. My adjustments are generally just a few degrees.

The point is your DG is not your heading. It is an estimate of your heading subject to a number of errors. Your heading is your path through the airmass.

Why would you say " your heading is your path through an airmass" ? Your heading ( actual magnetic heading, taking in account any errors) is the nose of the aircrafts' displacement from magnetic north.

 

[MAKG1]

Why would you say " your heading is your path through an airmass" ? Your heading ( actual magnetic heading, taking in account any errors) is the nose of the aircrafts' displacement from magnetic north.

No, it isn't. Not if you're in a slip or a skid. ATC will not compensate for lack of coordination, and neither will any flight planning application. Your heading is your direction within the airmass. This will be equal to the direction of your nose if you pilot with any degree of precision.

 

[RoscoeT]

Last post...

Don't tease us.

 

[vintage cessna]

No, it isn't. Not if you're in a slip or a skid. ATC will not compensate for lack of coordination, and neither will any flight planning application. Your heading is your direction within the airmass. This will be equal to the direction of your nose if you pilot with any degree of precision.

Well, the ol' FAA Airplane Flying Handbook defines heading as " the direction in which the nose of the aircraft is pointing during flight." That's it. So whether the aircraft is straight and level, slipping or skidding, that is the definition.

Granted, if you are in a wild slip or skid, your " track" or "course" will not be what ATC expected.

 

[Silvaire]

...Your heading is your path through the airmass.

This discussion just continues to get more and more bizarre. What on Earth is your "path through the airmass"? In reference to what exactly?

There is heading (what you read on the compass) and track (your course across the ground) The difference between the two is the wind correction angle. The third element in the triangle is your speed so aircraft going different speeds are going to have different headings to achieve the same track. ATC is going to assign you a heading to achieve the desired track they want you on. Doesn't matter to them if your compass is off or you are flying in a constant slip, if they want you 20 degrees to the left they can tell you that.

This is basic, fundamental navigation 101. You had to do this stuff as a student pilots.

What happened?

 

[taters]

who cares just fly the plane

 

[Lindberg]

Well at least everyone seems to be acknowledging now that an airplane can move laterally irrespective of any turning. That's some progress. For some reason I am having flashbacks to downwind turn discussions on rec.aviation.

 

[RotorDude]

This discussion just continues to get more and more bizarre. What on Earth is your "path through the airmass"? In reference to what exactly?

There is heading (what you read on the compass) and track (your course across the ground) The difference between the two is the wind correction angle. The third element in the triangle is your speed so aircraft going different speeds are going to have different headings to achieve the same track. ATC is going to assign you a heading to achieve the desired track they want you on. Doesn't matter to them if your compass is off or you are flying in a constant slip, if they want you 20 degrees to the left they can tell you that.

This is basic, fundamental navigation 101. You had to do this stuff as a student pilots.

What happened?

What happened is that IF you actually use the real unadulterated compass heading, and IF your nose points to where you flying (i.e. directly into the relative wind), THEN your wind correction angles will be correct and ATC will be happy.
But in real life, if you mess up your unslaved DG by forgetting to correct for drift, or fly uncoordinated, or your compass calibration is off, then the above is no longer true. So to make ATC happy and fly right in general, you need to make sure you fly coordinated and verify your DG heading matches your properly calibrated compass.

 

[MAKG1]

This discussion just continues to get more and more bizarre. What on Earth is your "path through the airmass"? In reference to what exactly?

The air. You have a speed and direction (in three dimensions) within the air. Unless you're flying in interstellar space or magnetic-dominated fluids, every point in space has a single well defined comoving velocity.

Those of us who calculate aircraft physics deal with this all the time. It is not at all an ambiguous definition, and it's not different conceptually from true airspeed.

If you wish to calculate the wind triangle in a slip, is the direction of the nose corrected for compass errors what you put into your E6-B? If you take the AFH as complete and perfect Gospel, that's the conclusion you would draw. You would be wrong by tens of degrees. In reality, the AFH is targeted at student pilots and doesn't consider the off nominal case for pedagogical reasons.

 

[RoscoeT]

Well at least everyone seems to be acknowledging now that an airplane can move laterally irrespective of any turning.

Wrong. Fly along straight and level and coordinated and then try to make the airplane move "laterally" (new flight path) without producing an intial turning (curving) flight path, slip or no slip. Cannot happen. Please post video. Have never seen this.

Now there will be 500 more posts arguing over what lateral movement means...which of course will be different with the air mass vs. ground reference, which hemisphere you're in, which direction the Coriolis effect is going, which eye you have open, and which ass cheek you're leaning on. Might also depend on the day of the week. We will all be proven slobbering idiots.

 

[vintage cessna]

The air. You have a speed and direction (in three dimensions) within the air. Unless you're flying in interstellar space or magnetic-dominated fluids, every point in space has a single well defined comoving velocity.

Those of us who calculate aircraft physics deal with this all the time. It is not at all an ambiguous definition, and it's not different conceptually from true airspeed.

If you wish to calculate the wind triangle in a slip, is the direction of the nose corrected for compass errors what you put into your E6-B? If you take the AFH as complete and perfect Gospel, that's the conclusion you would draw. You would be wrong by tens of degrees. In reality, the AFH is targeted at student pilots and doesn't consider the off nominal case for pedagogical reasons.

The FAA has established certain definitions for words or phrases used in air navigation. So, if you want to communicate with and comply with ATC instructions or FAR's you have no choice but to use those definitions. And if you want to communicate with a community of pilots and use definitions contrary to what has been established and accepted ( like your definition of heading) good luck.

 

[MAKG1]

Wrong. Fly along straight and level and coordinated and then try to make the airplane move "laterally" (new flight path) without producing an intial turning (curving) flight path, slip or no slip. Cannot happen. Please post video. Have never seen this.

How do you fly slips coordinated?

 

[MAKG1]

The FAA has established certain definitions for words or phrases used in air navigation. So, if you want to communicate with and comply with ATC instructions or FAR's you have no choice but to use those definitions. And if you want to communicate with a community of pilots and use definitions contrary to what has been established and accepted ( like your definition of heading) good luck.

It's not contrary to what ATC expects. Following your badly coordinated nose would fall into that category.

Just like ATC wants true airspeed, not what your ASI reads. If your DG is precessed, or broken or your coordination sucks, they expect you to follow a specific direction with respect to the air when they give you a "heading" for separation. They don't know what your DG reads.

 

[RoscoeT]

How do you fly slips coordinated?

Welcome to the spin zone. You don't. People are saying the airplane starts moving laterally as soon as you slip. If you're in coordinated flight, and want to move "laterally", to me this means the airplane "jumps" to a different flight path. You cannot change your flight path without turning, either coordinated turn or slipping turn.

If I was a more sensible person, I would not bother going in this circle for the N'th time. But I am not.

 

[vintage cessna]

It's not contrary to what ATC expects. Following your badly coordinated nose would fall into that category.

Just like ATC wants true airspeed, not what your ASI reads. If your DG is precessed, or broken or your coordination sucks, they expect you to follow a specific direction with respect to the air when they give you a "heading" for separation. They don't know what your DG reads.

ATC was my chosen profession. When I asked a pilot for his airspeed, I wanted his indicated airspeed. If you are queried by ATC for your airspeed, you better reply with what your ASI is indicating. The only time I ever asked a pilot for his TAS is when he was air filing a flight plan. The TAS in a flight plan is only useful so that the ATC computer can apply the forecasted winds at your filed altitude and then estimate your ground speed.

 

[Silvaire]

Wrong. Fly along straight and level and coordinated and then try to make the airplane move "laterally" (new flight path) without producing an intial turning (curving) flight path, slip or no slip. Cannot happen. Please post video. Have never seen this...

If you enter a slip while keeping the nose on a constant heading are not now going to be moving laterally?

If you enter a slip while keeping your ground track constant are you turning?

I'm not following you, a slip is a slip, the aircraft flys laterally in reference to it's longitudinal axis. When you land in a crosswind the aircraft is flying laterally in a slip to eliminate the drift caused by the crosswind?

It boggles my mind trying to figure just exactly what you guys think is happening when you are in a slip? Is the aircraft not flying laterally in regards to it's longitudinal axis?

Again, I feel as though I am at Cheers listening to multiple Cliff Clavens tell us all about Air Traffic Control and the intricate complexities of the simple aerodynamic slip.

 

[FastEddieB]

Just like ATC wants true airspeed, not what your ASI reads.

They do???

On a flight plan, maybe, but where else?

 

[RotorDude]

They do???

On a flight plan, maybe, but where else?

That's right, ATC want TAS on flight plan, IAS in flight.