Ground speed vs programmed speed

[Nick Dobda 24]

I'm getting into VATSIM now, and making plenty of rookie mistakes.

 

I flew out of DTW today, on the ACO5 SID.

 

I missed the special instructions "maintain 280K until advised by ATC"

​Controller got me at "390 across the ground at 12,000"

 

I was flying on VNAV SPD so when it crossed 10000 it accelerated as it should...

 

But my question is, to maintain 280K, (I've never did this before so I'm guessing at what I'd have to do) I would have to click SPD INTV and set it at 280K? Isn't this airspeed? Is ATC tracking my airspeed or ground speed? Is that 280K restriction airspeed or ground speed? Sorry if that's a dumb question.

 

More dumb question, how do I then get out of that 280 restriction when I'm cleared and back on to what the FMC has programmed in it?

 

Sorry, these sort of questions are coming up when I am starting to stray from the tutorial and fly in the ATC world. So much more info to digest on every flight.

[bholzer 1]

The speeds noted on the charts are always IAS - Indicated Air Speed.  Make sure your sim is set to display Indicated Air Speed, not True Air Speed, and you'll be good.

 

You could fly this several ways.  You could engage VNAV and engage the SPD INTV at 250KTS through 10,000ft.  Passing 10,000ft, increase speed to 280KTS.  Once ATC clears the speed restriction, then release the SPD INTV.  

 

Or you could fly it with ALT, VS and SPD settings in the MCP - set ALTITUDE to whatever you've been cleared to; VS to +3000 (or whatever you need to use to achieve the climbout) and SPD to 250KTS max.  Maintain that through 10,000ft.  Passing 10K, increase SPD to 280KTS.  Once ATC releases the speed restriction, engage VNAV.

 

That being said, bear in mind that there's more than one way to skin a cat  Get used to flying the airplane and then executing the procedures will become much easier.

 

And welcome to VATSIM!

[sosuflyer 30]

The speeds noted on the charts are always IAS - Indicated Air Speed. Make sure your sim is set to display Indicated Air Speed, not True Air Speed, and you'll be good.

 

You could fly this several ways. You could engage VNAV and engage the SPD INTV at 250KTS through 10,000ft. Passing 10,000ft, increase speed to 280KTS. Once ATC clears the speed restriction, then release the SPD INTV.

 

Or you could fly it with ALT, VS and SPD settings in the MCP - set ALTITUDE to whatever you've been cleared to; VS to +3000 (or whatever you need to use to achieve the climbout) and SPD to 250KTS max. Maintain that through 10,000ft. Passing 10K, increase SPD to 280KTS. Once ATC releases the speed restriction, engage VNAV.

 

That being said, bear in mind that there's more than one way to skin a cat Get used to flying the airplane and then executing the procedures will become much easier.

 

And welcome to VATSIM!

 

VS has no speed protection. You're first method would be what I would choose, but as for a second method, use FLCH with 250 until 10k, then change the speed window to 280.

[Alpha Floor 237]

But my question is, to maintain 280K, (I've never did this before so I'm guessing at what I'd have to do) I would have to click SPD INTV and set it at 280K? Isn't this airspeed? Is ATC tracking my airspeed or ground speed? Is that 280K restriction airspeed or ground speed? Sorry if that's a dumb question.

 

Hi Nick. ATC when giving instructions is always going to talk about either Indicated Airspeed (what you see on your speed-tape) or Mach Numbers at higher altitudes or during the cruise. As Ben said, make sure your sim is set for Indicated rather than True.

 

ATC on his radar tracks Ground Speed though. So it might be possible that even though you're flying at 280 Indicated, the ATC will see 380 GroundSpeed. That's not a problem, the ATC should know that.

 

It has happened to me sometimes when flying online that the ATC did not know the difference between IAS and GS. He would call and say "What's your speed" "280" "My radar says 380" "D'uh..."

 

 

 

VS has no speed protection

 

Let's not start the typical "V/S is a no-no" war please. V/S is one of several modes, is there for a reason, and can definitely be used during the flight if it's deemed convenient.

 

That said, during a climbout I agree with you in that I would rather select FLCH (or LVL CH on the 737). I generally favor "pitch on speed" modes, they feel more "natural" to me.

[scandinavian13 5,192]

 

 

But my question is, to maintain 280K, (I've never did this before so I'm guessing at what I'd have to do) I would have to click SPD INTV and set it at 280K? Isn't this airspeed? Is ATC tracking my airspeed or ground speed? Is that 280K restriction airspeed or ground speed? Sorry if that's a dumb question.
 
More dumb question, how do I then get out of that 280 restriction when I'm cleared and back on to what the FMC has programmed in it?

 

You would use SPD INTV. This is IAS, yes. ATC tracks ground speed, but the likelihood that you have a 110 knot tailwind at 12,000 is pretty slim (give or take a few knots for IAD>TAS conversion).

 

As long as you've only used SPD INTV, press SPD INTV again. Pretty sure this is covered in the tutorial.

 

I avoid setting open restrictions into the FMC. If it said "maintain 280 until FIXAA," then I'd put the speed in at FIXAA, but "until advised," to me, means use SPD INTV.

 

 

 

ATC on his radar tracks Ground Speed though. So it might be possible that even though you're flying at 280 Indicated, the ATC will see 380 GroundSpeed. That's not a problem, the ATC should know that.
 
It has happened to me sometimes when flying online that the ATC did not know the difference between IAS and GS. He would call and say "What's your speed" "280" "My radar says 380" "D'uh..."

 

Highly doubtful. I've been fussed at for 280 under 10 because the controller didn't understand how wind affected GS, but 110 knots is pretty extreme and will draw a question from a controller unless there is an observed trend (other aircraft are following the same trajectory, which lends to the idea that it's weather, and not an errant pilot).

[kevinh 409]

 

 

Let's not start the typical "V/S is a no-no" war please. V/S is one of several modes, is there for a reason, and can definitely be used during the flight if it's deemed convenient.

He's right though. VS has no speed protection. It's not that it shouldn't be used but it should be used with caution. If you are being asked to maintain an airspeed while changing flight level FLCH is surely your first choice mode. If you are asked to achieve a particular level over a waypoint then VS would probably be better. Horses for courses.

[Alpha Floor 237]

Highly doubtful

 

Kyle,

 

Those numbers might very well vary. It's an actual experience that happened to me when flying ONLINE on IVAO with a novice controller. If you're flying, say, at FL200 and 280 indicated, GS will be around (I did the calculation) 380 knots. At FL120 it would be 340 (maybe those 50kts difference was the wind) Someone who doesn't know the difference between IAS and GS might commit this mistake.

 

Yes: It's highly likely that once he reached 10.000 feet the aircraft accelerated to a climb speed of 320 or whatever, which could have granted that GS of 390. I was just exploring another possiblity and telling my own personal experience.

 

And honestly, I find it slightly offensive that you question my word like that. Maybe you didn't mean it like that and I didn't interpret your message correctly. If that's the case, I'm sorry in advance.

 

 

 

If you are being asked to maintain an airspeed while changing flight level FLCH is surely your first choice mode. If you are asked to achieve a particular level over a waypoint then VS would probably be better

 

Agreed!

[Nick Dobda 24]

Pretty sure this is covered in the tutorial.

 

I didn't find anything on spd intv. Tutorial talks about alt intv a few times. I realize I have the manuals do dig through to find an answer, but sometimes its easier to come here, and I tend to learn more insight from folks here anyway.

 

 

Make sure your sim is set to display Indicated Air Speed, not True Air Speed

 

Similar to the above, I could find the answer if I dug the internet, but on a brief google search the answer wasn't plain as day so I'll ask it here - how do I ensure that I am seeing indicated air speed?

 

ATC on his radar tracks Ground Speed though. So it might be possible that even though you're flying at 280 Indicated, the ATC will see 380 GroundSpeed. That's not a problem, the ATC should know that.

 

The controllers quote of "across the ground" got me confused. To me it sounded like he was tracking ground speed, which raised all those question marks about how speed restrictions are determined in the air if the winds are constantly changing.

 

 

but "until advised," to me, means use SPD INTV.

 

I think I'd agree with you in this scenario. So it seems click once on SPD INTV, set to the restriction, then click SPD INTV again to get out of it and back on the FMC program.

 

I have another question on this INTV button... from tutorial #2:

 

"Be very careful with this function [ALT INTV] as every press of it when not

in VNAV ALT deletes the next restriction along the route for the

current phase of flight (climb or descent). You could seriously

mess up your route if you pressed it a bunch of times and had a

lot of restrictions get removed accidentally."

 

does clicking SPD INTV delete speed restrictions, or does it simply override the speed restriction - as in it is a temporary state that doesn't change the FMC program. I don't want to potentially delete speed restrictions that have been so deliberately programmed into the SIDS and STARS.

 

 

And I'll slide in one more question about VATSIM control-

 

I crossed my T/D on my route, and let it slide for about 5 mins till I finally had to ask the controller if I could descend. At that time he did clear be to begin descent. But it forced me to ride the spoilers down and descend much faster to try and catch back to the VNAV path... I never did catch it, and when I was instructed to cross certain points along my STAR at certain altitudes... and speeds... things got really stressful. If I was following the FMC everything would have worked out automatically with a whole lot less stress. When is it appropriate to remind a controller that I've passed my preferred T/D? Why did he miss it and does this happen often?

 

And another curiosity - when I passed the T/D, eventually the speed decayed down to just above flaps up. The FMC commanded the plane to slow down. I'm assuming this was on purpose, but why? Does the FMC know the further beyond T/D I go, the worse off I am, so it commands to slow down to minimize the trouble I'm going to have descending? If so thats pretty slick I guess..?

[scandinavian13 5,192]

 

 

Those numbers might very well vary. It's an actual experience that happened to me when flying ONLINE on IVAO with a novice controller. If you're flying, say, at FL200 and 280 indicated, GS will be around (I did the calculation) 380 knots. Someone who doesn't know the difference between IAS and GS might commit this mistake.

 

The numbers may vary, yes, but this wasn't FL200, it was 12,000. In the United States - where the incident occurred - our TRACONs rarely get into the Flight Levels. Given the amount of work that it generally requires to get to the level of experience required for a Center certification, a controller will understand TAS increase, and the interaction of wind by that point. A TRACON controller might miss the concept early on because a tower controller does not usually focus on it (at least on VATSIM). Given that TRACONs are usually kept down below the flight levels, it's not as likely that you're going to get a lesser experienced person who unfamiliar with the concept of TAS and wind.

 

Now, I did not make the TAS calculation in my earlier post. That calculation would get us about 347 for a compliant aircraft (flying 280 IAS), which would mean that there would have to be a tail wind of 43 knots to get 390 across the ground. That's not entirely unreasonable at 12,000 heading eastbound on a normal day, but it may draw the attention of the controller if it was the first aircraft he'd seen through that corridor. As such, a quick query is neither unreasonable, nor is it implicitly accusatory.

 

A query from the controller should be relatively simple:

 

Compliant

Controller: "[ACID], say indicated airspeed."

Pilot: "280 indicated, [ACID]."

Controller: "[ACID], roger."

 

Non-compliant

Controller: "[ACID], say indicated airspeed."

Pilot: "310 indicated, [ACID]."

Controller: "[ACID], roger. The ACO5 SID has a speed restriction of 280 knots until advised. [Corrective action as necessary.]"

 

 

 

And honestly, I find it slightly offensive that you question my word like that. Maybe you didn't mean it like that and I didn't interpret your message correctly. If that's the case, I'm sorry in advance.

 

Offense is all what you want to be, or allow yourself to be, offended by. There's no need to be offended by my disagreement with your representation of the situation. I'm disagreeing with the point you tried to make - that the controller was somehow missing the wind component - which is nothing to be offended by. If it is, then you might want to reconsider what you've been posting, since a lot of it has been heavy on opinion (re: your other thread). Emotion does not belong in discussion.

 

 

does clicking SPD INTV delete speed restrictions, or does it simply override the speed restriction - as in it is a temporary state that doesn't change the FMC program. I don't want to potentially delete speed restrictions that have been so deliberately programmed into the SIDS and STARS.

 

Nope. SPD INTV is simply a toggle: into speed override and out of speed override.

 

 

 

I crossed my T/D on my route, and let it slide for about 5 mins till I finally had to ask the controller if I could descend. At that time he did clear be to begin descent. But it forced me to ride the spoilers down and descend much faster to try and catch back to the VNAV path... I never did catch it, and when I was instructed to cross certain points along my STAR at certain altitudes... and speeds... things got really stressful. If I was following the FMC everything would have worked out automatically with a whole lot less stress. When is it appropriate to remind a controller that I've passed my preferred T/D? Why did he miss it and does this happen often?

 

A controller usually uses an order of magnitude above the pilot rule of thumb. The pilot rule of thumb is 3 x Distance to Required Altitude. The controller rule of thumb is 4 x the Distance to Required Altitude. That being said, the instruction - in a normal situation - should come well in advance of the T/D marker. If you're coming up on the T/D, simply say "[FACID], we're coming up on our T/D - any chance for lower?" They'll usually give it to you on the spot. It usually happens when you have a VATSIM controller who is covering all kinds of airspace on their own (having to cover for a busy TRACON as an example).

 

"Unable" is also a word that pilots forget about way too much. Note how you said "stressful." Why was it stressful? It was stressful because by someone else's fault, you were put in a tougher spot to meet requirements.  You can very easily say "I got a late descent so I'm above profile." The controller will likely just say "roger" (implicit acceptance of being above profile, though you may clarify if you wish), or they may say "roger, descend and maintain [X]," which cancels all altitude restrictions published. Don't put yourself in a bad spot because someone else forgot about you. Speak up and let them know. If it's during an event, I very rarely forget to pass a message "down line" to the next controller (or two) to let them know that I [screwed] up and that you'll be above profile. They'll just need to be a little more vigilant about crossing traffic flows that cross above the STAR profile (the TERPZ SID out of BWI and the HYPER into IAD, as an example).

 

 

 

And another curiosity - when I passed the T/D, eventually the speed decayed down to just above flaps up. The FMC commanded the plane to slow down. I'm assuming this was on purpose, but why? Does the FMC know the further beyond T/D I go, the worse off I am, so it commands to slow down to minimize the trouble I'm going to have descending? If so thats pretty slick I guess..?

 

Energy compensation. You can "make up" the difference in profile by increasing your rate of descent. This, of course, will "overspeed" your IDLE PATH. In other words, you will descend fast enough such that you will also increase your speed even with idle throttles. Because of this, being below the IDLE PATH speed gives you an additional amount of time to overspeed your IDLE PATH to get increased descent rates.

[Nick Dobda 24]

I got stressed mostly because it was still only my 8th flight on VATSIM. I've yet to have a perfect flight. And the controllers speak fast and not always very clearly. Im still unable to anticipate what is going to be said, so when they blurt something out, sometimes I miss it, or have to think for a few seconds as to what it is likely that they said. In time I'll get the hang of it, but its still way early.

 

I was trying to make up the profile, so I descended on idle and played with the V/S with spoilers up. As you mentioned, my speed was creeping up... and up... and I was getting closer to my point in space (10,000') I knew I was going to have to scrub the speed back down to 250. I had the altitude prediction ring on the main display right where I wanted it to, but knew that because I would have to level out and scrub off that speed before I actually hit that altitude, it would put me high on the next target... I was seeing that things were going to snowball and it was going to be a fight all the way in. I just wasn't used to it

 

Other random questions keep coming up, like he had me on vectors to final..... so I was on HDG select on the heading he gave me, but he didn't instruct me to intercept the ILS, he cleared me on the visual - and let him know when the runways in sight- so I'm coming in on his heading, then the ILS becomes active, and im in VOR mode, so the plane starts to turn to intercept the ILS (while IM still looking out the window trying to identify the runway). Of course now I'm thinking great, I'm going off his heading without his clearance, so I click off VOR and back onto his heading... at which time he finally instructs me to turn and clears me still on the visual on a heading towards the runway. So its back to clicking on the VOR to get back on the ILS. Then eyes back out front to find the runway.

 

SO then I'm thinking I must have did something wrong, or maybe its normal to be cleared for a visual approach (why would it be when i just flew an IFR route, you'd think it would be obvious I'd be taking advantage of ILS).

 

Like I said.. just stressful while still in the learning phase of this deal.

[JoeDiamond 67]

 

 

But my question is, to maintain 280K, (I've never did this before so I'm guessing at what I'd have to do) I would have to click SPD INTV and set it at 280K? Isn't this airspeed? Is ATC tracking my airspeed or ground speed? Is that 280K restriction airspeed or ground speed? Sorry if that's a dumb question.

 

My personal technique would be to put 280 on the climb page prior to departure.  Later, once the restriction is lifted I would either select ECON or whatever speed I wanted on the climb page.

 

Speed intervention would work as well.  If I know about the speed restriction in advance, as you would on a SID like this, I prefer to use the climb page.  Speed intervention requires action later and if I give myself the chance to forget something later I probably will.

[scandinavian13 5,192]

 

 

Other random questions keep coming up, like he had me on vectors to final..... so I was on HDG select on the heading he gave me, but he didn't instruct me to intercept the ILS, he cleared me on the visual - and let him know when the runways in sight- so I'm coming in on his heading, then the ILS becomes active, and im in VOR mode, so the plane starts to turn to intercept the ILS (while IM still looking out the window trying to identify the runway). Of course now I'm thinking great, I'm going off his heading without his clearance, so I click off VOR and back onto his heading... at which time he finally instructs me to turn and clears me still on the visual on a heading towards the runway. So its back to clicking on the VOR to get back on the ILS. Then eyes back out front to find the runway.

 

He's supposed to let you know ahead of time what to expect. Make sure that you're paying attention to that if it's given (if it wasn't, it's a little bit of his fault, but do keep in mind that unless the weather is poor, you're getting the vis). Clearance for the vis does not preclude you from using the ILS if you want to, provided you don't start flying all over the place to capture the LOC.

 

 

 

SO then I'm thinking I must have did something wrong, or maybe its normal to be cleared for a visual approach (why would it be when i just flew an IFR route, you'd think it would be obvious I'd be taking advantage of ILS).

 

Vis is the predominant instruction, unless the weather is poor, even if you're IFR. It's easier for everyone involved. Many operators will specify that the crews supplement visual cues with those provided by the ILS, but it's still a visual approach.

 

 

 

Like I said.. just stressful while still in the learning phase of this deal.

 

To be honest, you're probably better off taking a plane that is simple, or a plane that you have mastered online first. That way, you're not drinking from two fire hoses at once. The 737 is a handful. If you aren't up to speed with all of the tools the MCP has to offer, you're going to get behind the aircraft, which is going to cause a load of stress. Taking a 172 up for a quick jaunt within a controller's coverage area will help you get a feel for when the instructions come at you, and what message they contain.

 

Check out the pilot ratings from ZLA. Even if you don't do them online, the info they contain will really help you, even if you just read the transcripts:

http://pilotcerts.laartcc.org/page/ratings.html

[Ralgh 43]

My personal technique would be to put 280 on the climb page prior to departure.  Later, once the restriction is lifted I would either select ECON or whatever speed I wanted on the climb page.

 

Speed intervention would work as well.  If I know about the speed restriction in advance, as you would on a SID like this, I prefer to use the climb page.  Speed intervention requires action later and if I give myself the chance to forget something later I probably will.

Chicago has a similar 250kt restriction. Putting the speed on the climb page then selecting ECON is the way we typically did it on the 737 when departing there.

[Nick Dobda 24]

Chicago has a similar 250kt restriction. Putting the speed on the climb page then selecting ECON is the way we typically did it on the 737 when departing there.

You folks come through again, thanks for the suggestions.

 

 

Check out the pilot ratings from ZLA. Even if you don't do them online, the info they contain will really help you, even if you just read the transcripts:

 

Thanks Ill look into it.

 

Downside to a simpler plane, none of my simple plans can read the sids and stars. My favorite thing about the NGX is how complicated it is. Trial by fire, sure I'll lose some extra hair and have a little higher blood pressure but ill come out better

[scandinavian13 5,192]

 

 

Downside to a simpler plane, none of my simple plans can read the sids and stars. My favorite thing about the NGX is how complicated it is. Trial by fire, sure I'll lose some extra hair and have a little higher blood pressure but ill come out better

 

Yeah, but it'll help you to understand what a SID and STAR truly are by flying them yourself. The FMC of an aircraft should never be used as a crutch, just as the AP shouldn't be used as a crutch. The FMC may fail in some way, as the AP may fail. The aircraft should still make it safely to the ground.