Nautical Air Miles (NAM)

[NoPax]

A few months ago, while studying towards my ATP written, there was a couple of flight planning questions relating to Nautical Air Miles.

Recently, I got to fly in a CJ1, from Austin to Dallas, and we climbed to FL220. The pilot wanted to climb higher - maybe FL280, and new to the whole jet experience, I didn't say anything (& we didn't get higher).

Its about 165NM, and I seem to recall the NAM chart for the 737 recommending a lower altitude (?).

What exactly are Nautical Air Miles, and how could a pilot flying Part 91 use this to their advantage - ie how can I explain that FL280 would be a waste of time?

Thanks

 

[Stby One]

NAM is Nautical Ground Miles corrected for wind.

Example, 1 hour flight, ground distance 400NGM, headwind component 50kt = 450NAM

What you are thinking of is optimum altitude for short flights. For the B737 there is a short cruise table that gives you an optimum altitude for that gives you at least 1 minute at cruise level.

FL 280 may be a waste in a 737, but i might be closer to optimum for a light jet, you'd have to go into the performance manuals to get the exact answer for that aircraft.

Hope that answers your question

 

[NoPax]

NAM is Nautical Ground Miles corrected for wind.

Example, 1 hour flight, ground distance 400NGM, headwind component 50kt = 450NAM

Thanks.

I'll have to do a little digging in the manuals to find the optimum altitude for short cruise flights.

Now I just have to learn what all the buttons do!

 

[FlyDouglasJets]

Nautical air miles or often called ESAD (equal still air distance) is the NGM (nm ground miles) corrected for wind.

formula for NAM is;

NAM = NGM * (avg TAS/avg GS)

AUS-DAL = 200 nm (NGM)

TAS = 400 kts
Wind = 30kts headwind -
GS = 370 kts

NAM = 216 nm

 

[FlyDouglasJets]

Higher is not always better, if it decreases your Groundspeed substantially, due to a strong jetcore headwind.

 

[FlightOpsAB]

Higher is not always better, if it decreases your Groundspeed substantially, due to a strong jetcore headwind.

Yes, and that concept compltely escapes some of the pilots. There have been far too many times that I have planned a flight at say 340 and at the first position report they say they're at 410......... The fact that you can go that high does not necessarrily mean you're gonna burn less gas. Just fly the damn flight plan already....
Whew, sorry

 

[FlyDouglasJets]

Yes, and that concept compltely escapes some of the pilots. There have been far too many times that I have planned a flight at say 340 and at the first position report they say they're at 410......... The fact that you can go that high does not necessarrily mean you're gonna burn less gas. Just fly the dang flight plan already....
Whew, sorry

True dat, and niether is going great-circle direct the most efficient path from A-B. "Ahh....my FMC planned arrival fuel is showing less than :30 minutes, after I took that giant 1000nm direct routing about 2hrs ago". Where should I land?

You can't train stupid.

The Dude

 

[Bart Simpson]

...edited for no factual content

 

[NoPax]

niether is going great-circle direct the most efficient path from A-B. "Ahh....my FMC planned arrival fuel is showing less than :30 minutes, after I took that giant 1000nm direct routing about 2hrs ago".

OK, I think I'm missing something. I thought the shortest distance between two points was direct.

If you are talking about jet-stream winds, then I can see that, or am I missing something else?

 

[FlightOpsAB]

OK, I think I'm missing something. I thought the shortest distance between two points was direct.

If you are talking about jet-stream winds, then I can see that, or am I missing something else?

You got it, a direct might be a good idea some of the time, but def not ALL the time. Jetstream, tropopause, etc. Of course the change in fuel burn might not be all that great, but it adds up.

 

[Gorilla]

We often deviate from the flight plan based upon two primary tools... the FMC fuel burn computation, and PIREPS. The goal of the flight is safety, comfort, on-time, and economy, in that order.

Situation 1: FP is 340. Cargo drops off significantly in the chocks. Winds aloft don't vary much from FL to FL. Higher = better

2: FP 360. Level 360, we "plug" 380 into the box. FMC says "yes fool, 380 will save 200 lb of fuel at destination." All else being equal, up we go.

3: FP 380. The ride is abominable. Pirep says 340 is smooth. Down we go to keep our flight attendants safe and passengers' lunches in their stomachs, where they belong.

4: FP 380. The forecast winds don't show up. PIREP says lower/higher is better. Once again, we change altitudes.

5: FP 370. Center says, upon initial climb-out, "The ONLY available altitudes due to traffic are 410 or 330. Pick one." This happens quite often.

It's like a battle. No plan survives first contact with the enemy. There are so many variables, it is surprising to me if we fly the flight plan exactly as it is printed.

edited: My language was inappropriate in the original post! :0

 

[FlightOpsAB]

Agreed, Gorilla. Those are all good reasons and that's my point. The key is communication. If you are deviating from your planned FL why not tell your friends back in DX why you did that, so we can plan accordingly. We all plan for the same team, right?

 

[Gorilla]

Agreed as well, but the impression I got from the thread so far was "Why don't the pilots fly the flight plan as it is printed, preflight?" Most of us assume that automatic position reports tell dispatch and others where we are, and at what FL. It seems about the only info not automatically sent is the ride conditions.

 

[pilotyip]

Get out your sextant

A NAM is one minute of elevation of a celestial body upon a great circle. 60 minutes of evaluation equals on degree. When shooting the North Star it will very closely approximates your latitude in degrees, it is on the horizon at the equator, and 90-degree overhead at the North Pole. This made it very easy for a navigator to convert celestial sighting to distances upon the surface of the earth.

 

[NoPax]

A NAM is one minute of elevation of a celestial body upon a great circle. 60 minutes of evaluation equals on degree. When shooting the North Star it will very closely approximates your latitude in degrees, it is on the horizon at the equator, and 90-degree overhead at the North Pole. This made it very easy for a navigator to convert celestial sighting to distances upon the surface of the earth.

No disrespect but, I think your on an entirely different book, nevermind page.

I was originally asking how a pilot could use the Nautical Air Mile, when planning a flight - specifically what exactly it is (I couldn't remember the formula - NM*(avg. TAS/avg. GS), and how I could explain this to a fairly low-time CJ1 pilot, when suggesting the altitude to fly at for shorter trips.

It would be like flying from Willow Run to Traverse City MI, and requesting FL340 - just because you can get that high, doesn't mean its the most efficient way to do it in your Falcon.

Interesting post anyhow. BTW is a sextant approved for IFR navigation in RVSM airspace, under part 135???

 

[FlyDouglasJets]

primary tools... the FMC fuel burn computation

The FMC fuel burn predictiong, if going DCT TO a fix 1000nm will use the following logic (at least the Honeywell units)

Predicted Groundspeed and thus segment time, and fuel burn will be based on the following;
current wind component, used for a decreasing mix up to 250~500nm ahead of the jet, and then a mix of that wind and the FMC wind for the next down-range FIX (which might be 900+nm in front of the jet).

The summary, the FMC fuel burn, especially during the WINTER, might lull one into a false sense, as this wind "mixing" may perhaps totally overlook (garbage in/out) a polar jetcore on the nose @ 150kts somewhere out near 500nm ahead.

The outcome ain't pretty, the predicted arrival fuel on the FMC may perhaps cause a new seat cushion post-arrival.

DD

 

[FlyDouglasJets]

Nopax- how about the tried and true formula for short-range flts (>300nm).
NAM * 100 = FLxxx

NAM = 200nm fly @ FL200
NAM = 150nm fly @FL150

 

[NoPax]

how about the tried and true formula for short-range flts (>300nm).
NAM * 100 = FLxxx

NAM = 200nm fly @ FL200
NAM = 150nm fly @FL150

I think you meant <300NM [less than], but ok that works too - and keeps him out of the 30s, clearing the way for your boys and girls.

 

[pilotyip]

nopax, the sextent was RNP-25. No one uses them anymore that I know of.

 

[Vector4fun]

Recently, I got to fly in a CJ1, from Austin to Dallas, and we climbed to FL220. The pilot wanted to climb higher - maybe FL280, and new to the whole jet experience, I didn't say anything (& we didn't get higher).

This may or may not be of interest to you, but AUS to DAL you'll likely always get AUS CWK2 NAVYS DUMPY2 DAL; and you'll never get higher than FL220, unless it's middle of the night. That's a Center restriction, and it's published on the CWK2 departure...

And since this is a dispatcher's forum, is it the dispatchers, or the pilots who never notice max altitudes on certain departure transitions, and thus constantly file FL290 and above on a transition that's clearly published for flights at or below 120? :erm: