Why TAS instead of GS on flight plan form?

[flhrci]

I am looking for the answer to this question and I can't find it any where. Any one know why we don't use ground speed on a flight plan? I think that info would help in a SAR effort more than TAS.

Thanks,

David

 

[jesse]

I am looking for the answer to this question and I can't find it any where. Any one know why we don't use ground speed on a flight plan? I think that info would help in a SAR effort more than TAS.

Thanks,

David

Kind of hard to fill in a value that's impossible to know before you're in the air. Groundspeed before flying is just a prediction that is often more wrong than it is right. It also changes a lot (often dramatically) during any flight of distance.

 

[frfly172]

Kind of hard to fill in a value that's impossible to know before you're in the air. Groundspeed before flying is just a prediction that is often more wrong than it is right. It also changes a lot (often dramatically) during any flight of distance.

Good answer ,Jesse

 

[poadeleted20]

For IFR operations, TAS is more important, as that gives the controller the information needed to separate you from preceding/succeeding aircraft regardless of the actual vs forecast wind. For VFR, it really doesn't matter -- they have your route and ETE, and that's enough to help find you.

 

[flhrci]

Kind of hard to fill in a value that's impossible to know before you're in the air. Groundspeed before flying is just a prediction that is often more wrong than it is right. It also changes a lot (often dramatically) during any flight of distance.

I agree with you but if the proper flight planning is done prior to flight then you have a predicted ground speed already. As for not knowing the ground speed until in flight, you are only goign to get that info from a GPS which came after the invention of the flight plan form. There is no way without a GPS to accurately get the wind information while in flight to make the proper ground speed calculation.

And TAS is based on calculations that are realistically educated guesses based on weather guessing and aircraft performance numbers that once leaving the factory aren't 100% reliable.

So for right now, I don't have a satisfactory answer to m question.

David

 

[Everskyward]

I agree with you but if the proper flight planning is done prior to flight then you have a predicted ground speed already. As for not knowing the ground speed until in flight, you are only goign to get that info from a GPS which came after the invention of the flight plan form. There is no way without a GPS to accurately get the wind information while in flight to make the proper ground speed calculation.

What are you going to fill in for the GS if you are going a long way and the wind changes?

 

[flhrci]

What are you going to fill in for the GS if you are going a long way and the wind changes?

Ok, that makes sense!

The TAS is a static number that is not expected to change through out the flight that would give someone an idea how far you would have gone. Got it! So simple. That is basically what I was looking for.

David

 

[dmspilot]

What are you going to fill in for the GS if you are going a long way and the wind changes?

Or you fly to a VOR and change course.

Or file with a brief stop at an intermediate airport.

 

[Wheels]

As for not knowing the ground speed until in flight, you are only goign to get that info from a GPS which came after the invention of the flight plan form. There is no way without a GPS to accurately get the wind information while in flight to make the proper ground speed calculation.

It is easy to determine ground speed without a GPS and accurate wind information isn't required to compute it. If you know how far apart your checkpoints are all you need to do is time how long it takes you to get from one to the next. Distance divided by time equals ground speed.

 

[jordane93]

Kind of hard to fill in a value that's impossible to know before you're in the air. Groundspeed before flying is just a prediction that is often more wrong than it is right. It also changes a lot (often dramatically) during any flight of distance.

This.

 

[Silvaire]

...There is no way without a GPS to accurately get the wind information while in flight to make the proper ground speed calculation....

 

[EdFred]

You and me both. I guess crossing radials, and all those intersections on charts with distances between them don't mean anything. Just for decoration, I suppose.

 

[Silvaire]

And why did these things look so complicated if you couldn't do anything with them?

 

[flhrci]

You and me both. I guess crossing radials, and all those intersections on charts with distances between them don't mean anything. Just for decoration, I suppose.

I was waiting to get beat up on this. I simply forgot there were other ways to calculate it. I am not a math whiz so I forget about things like time and distance formulae.

Such critics in here. Should have just spent another year or two to find the answer on my own. Next time I just won't ask a question.

David

 

[Silvaire]

Don't take it so hard David, it was just the manner in which you said it "there is no way without a GPS" that practically begged for a lashing but to be honest, I've been flying for over 45 years and if I were to pull out an E-6B right now I'd have to have the user manual as well. We've all become slaves to the magenta line to some degree whether we want to admit it or not.

 

[philiplane]

ATC provides separation services, and they need TAS to determine how to separate planes of different performance. Estimated ground speed is not helpful to them since they are watching dots on a radar screen under changing wind conditions. TAS allows predictions of conflicts, then radar tracks confirm that those predictions are or are not accurate, ATC then adjusts assigned headings and altitudes to maintain separation.

 

[EdFred]

I was waiting to get beat up on this. I simply forgot there were other ways to calculate it. I am not a math whiz so I forget about things like time and distance formulae.

Such critics in here. Should have just spent another year or two to find the answer on my own. Next time I just won't ask a question.

David

Aren't you a CFI though? I thought you were.

 

[flhrci]

Aren't you a CFI though? I thought you were.

I am but I don't teach a whole lot and I forget stuff like any other human. I actually was never taught a reason why we use TAS on flight plan forms. I am prepping to teach x-c planning here soon to my current student. He is about to solo. So I just happened to think up that question that he may ask me.

Wether or not I am a CFI doesn't mean I know everything about flying, that's for sure.

David

 

[EdFred]

I am but I don't teach a whole lot and I forget stuff like any other human. I actually was never taught a reason why we use TAS on flight plan forms. I am prepping to teach x-c planning here soon to my current student. He is about to solo. So I just happened to think up that question that he may ask me.

Wether or not I am a CFI doesn't mean I know everything about flying, that's for sure.

David

I don't think any of us know everything. I just hold those of us who allow others to terrorize a skies to a little bit higher standard. We should know a bit more....should. I don't recall going into much detail during learning about it either, I think that might have just been one of those things that made sense from the beginning to me. On the other hand why VA went down when weight went down took me a long time ti really get why. I usually just nodded my head and went along with it. It was probably well into my commercial training before the light bulb went off on why.

 

[Clark1961]

And why did these things look so complicated if you couldn't do anything with them?

They are just to impress the unwashed masses...

 

[Stewartb]

I've always planned for duration, not MPG. But what the heck, I rarely plan.

 

[Henning]

I agree with you but if the proper flight planning is done prior to flight then you have a predicted ground speed already. As for not knowing the ground speed until in flight, you are only goign to get that info from a GPS which came after the invention of the flight plan form. There is no way without a GPS to accurately get the wind information while in flight to make the proper ground speed calculation.

And TAS is based on calculations that are realistically educated guesses based on weather guessing and aircraft performance numbers that once leaving the factory aren't 100% reliable.

So for right now, I don't have a satisfactory answer to m question.

David

I can't remember once when winds matched forecast.

 

[Everskyward]

I actually was never taught a reason why we use TAS on flight plan forms.

I don't specifically remember being taught that either but guessing it is/was used as a guide for separation of IFR traffic. But with radar more available now I don't know how much it is used. Maybe a controller can enlighten us.

 

[Brad Z]

I agree with you but if the proper flight planning is done prior to flight then you have a predicted ground speed already. As for not knowing the ground speed until in flight, you are only goign to get that info from a GPS which came after the invention of the flight plan form. There is no way without a GPS to accurately get the wind information while in flight to make the proper ground speed calculation.

And TAS is based on calculations that are realistically educated guesses based on weather guessing and aircraft performance numbers that once leaving the factory aren't 100% reliable.

So for right now, I don't have a satisfactory answer to m question.

David

As others mentioned, winds aloft change along your route. But there's another part of your premise that's flawed:

1) flight plans are routinely filed days before the flight is conducted. TAS doesn't change significantly, so there's no need to do ground speed calculations prior to filing flight plans. It also helps with flow control, and is less prone to calculation errors.

2) you suggest that a GPS is required to determine ground speed. I'm not that old, but when I learned to fly in 1993, we used our nav logs and visual checkpoints to calculate ground speed using a watch. Not much different then how GPS does it now, albeit quite a bit slower.

FWIW, as a CFI, I'll be the first to admit I don't have all of the answers. But with the experience and training of a CFI comes the expectation of applying critical thinking. If a student asked me the question you asked, I'd suggest to the student we give it a try. After our first course change, or recalculation of winds aloft because of distance, or a flight delay, I think the answer would be real apparent. I'm not beating up on you...just giving you another way to approach the issue.

Some of my best learning moments were when a pilot asked me a question I didn't readily have an answer for.