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Plotting the Hawaii "Romeo" Routes

More about this: Plotting 101

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Photo: Plotting Required, from 8900.1, Vol 4, Ch 1, ¶4-80

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Dear Eddie,

Please settle a bet for us. We fly from California to Hawaii almost every other week and have all the Romeo Routes memorized. We all agree that we need to plot over the North Atlantic because those tracks change twice a day. But the Hawaii tracks have been set in stone as long as any of us can remember. So we think there is no need to plot when flying the fixed tracks between California and Hawaii. And that also means we don’t have to do the ten-minute post position plot either. That’s right, isn’t it?”

Signed, R. Fader
Fort Lee, New Jersey

Mister Fader

No, that’s not right. Just because the route doesn't change on a daily basis doesn't mean you or your FMS will not make mistakes. The distance between ground-based navigation aids between California and Hawaii far exceeds those required by FAA Order 8900.1, Volume 4, Chapter 1, Paragraph 4-80.A, which says you must plot.

What the regulation says is that, “Plotting procedures are required for all turbojet operations where the route segment between the operational service volume of ICAO standard ground-based navigational aids exceeds 725 NM.” If you are flying a turboprop, the distance decreases to 450 nautical miles.”

So what is the service volume on an ICAO standard ground-based navigational aid? Depending on your altitude, that can be anywhere from only 25 nautical miles for an NDB or up to 130 nautical miles for a VOR.

So, as a rule of thumb, I’ve always plotted if I was further than 800 nautical miles from the nearest usable VOR.

That same regulation, by the way, also specifies the 10-minute post position plot, so the same rule applies. You do need to do a post position plot.

Eddie

On Course or Established

Dear Eddie,

When can I consider myself “on course” or “established” for an approach? Everyone says just wait until the CDI is “off the wall” and you will be okay. I want to descend as soon as possible but how can I be sure I have obstacle clearance?

Signed, R. Fader
Fort Lee, New Jersey

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Photo: Proceeding Direct, from AFM 51-37.

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Mister Fader

I flew my first ILS looking at a course indicator and was told the same thing: I could consider myself on course when the CDI came "off the wall."

On a procedure turn, for example, it was okay to descend to the inbound altitude once the CDI was no longer fully deflected.

Years later I adopted a "centered or nothing" attitude, thinking I was better than a nearly fully deflected needle.

But it begs the question, do we have the required obstacle clearance when the needle just comes off the wall. If not, what about one dot?

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Photo: Localizer final trapezoid, from Eddie's notes.

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FAA Handbook 8083-15B, Instrument Flying Handbook, says one-quarter scale deflection means the airplane is aligned with the runway and full-scale deflection shows when the aircraft is 2.5° either side of centerline.

You cannot come up with a one size fits all rule about what full scale CDI deflection means. But doing the math, there are times when the needle comes off the wall a little early. I show that math on this website page: http://code7700.com/ils.htm#oncourse

So full scale is too much, waiting until the needles are centered can leave you too high for the procedure. But the FAA guidance is ambiguous. I think you should look at the ICAO Regs on this, ICAO Doc 8168, Procedures for Air Navigation Services, or PANSOPS, to be specific.

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Photo: ICAO "On Course," from ICAO Doc 8168.

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That regulation says the tracking tolerance of the localizer/azimuth is much more narrow than for non-precision approaches and gives us the worst case scenario. In that scenario, “half scale deflection” keeps you in the protection area.

So in my opinion, that’s a good time to consider yourself on course or established: half scale deflection.

Eddie

Half of What Wind and All of What Gust?

More about this: Landing.

Eddie,

We all know we have to add half the wind and the full gust increment to our approach speeds. But do you add half the wind, or half the headwind?

Signed, R. Fader
Fort Lee, New Jersey

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Photo: Crosswinds, MROC, 21 Feb 2012, Bernal Saborio

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Mister Fader,

This has vexed me for a long time, but there is a more important question. But first, to answer your question. It depends on your manufacturer. Most simply state the wind itself, they don't want you doing the headwind component. Gulfstream, for example:

[G450 Airplane Flight Manual §5.11] If gusty wind conditions are present, add ½ of the steady state wind plus the full gust value to a maximum additive of 20 knots (VREF + 20). VREF will still be the target speed at the threshold.

Bombardier aircraft have a similar statement.

The other method is used by Boeing, in the 737NG, for example:

[Boeing 737 GN FCTM, p. 1.11] If the autothrottle is disconnected, or is planned to be disconnected prior to landing, the recommended method for approach speed correction is to add one half of the reported steady headwind component plus the full gust increment above the steady wind to the reference speed. The minimum command speed setting is VREF + 5 knots.

Dassault has a similar method and they have an even better explanation:

[F900EX CODDE2, ] Approach speed (VAPP) is the result of: VREF + wind correction. For wind correction (maximum 20 kt): apply half headwind + full gust increment. COMMENTS: The gust value should be taken into account whatever the wind direction is. For example for RWY 18, wind 120/20G30 given by the ATC: the steady state headwind component is 10 kt (crosswind component is 17 kt) and the full gust is 10 kt so the wind correction should be 15 kt (which is less than 20 kt).

So the technical answer depends on your aircraft manuals, but I think the right answer, the one that takes physics into consideration, has more to do with my bigger concern: stall speeds and stopping distance.

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Photo: Landing flare energy, from Eddie's notes.

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Most aircraft use a VREF that is 1.3 times the stall speed, though some aircraft get as low as 1.23. You might think that 30 or 23 percent above stall speed is ample, but keep in mind the airplane has a downward vector which is aimed usually 3 degrees along the acceleration of gravity. You will need energy to stop that acceleration and that energy comes from your forward velocity. As you pull back on the yoke or stick, you are trading excess airspeed for a decreased downward vector.

Here's where it gets tricky. Your landing distance is more than likely based on touching down at VREF. Some manufacturers are explicit about this. Even though they want you to make the wind additive, they want you landing at VREF.

So let's say you do that. You are just a few feet off the ground at VREFand your negative gust hits. Now you have less energy to flare. Or lets say the positive gust hits. Now you are too fast for your landing data. What to do?

If I were writing the manual, I would recommend using half the headwind component plus all the gust, and then I would base my landing distance performance number on the highest possible touchdown speed. My AFM only provides for a 10 knot additive when computing landing distances and in a typical scenario that adds between 15 and 25 percent to my landing distance. If I know my required landing distance is more than 3/4 of the available runway, I know I will have to worry about the gust additive and perhaps find someplace else to land.

Eddie

References

Air Force Manual (AFM) 51-37, Instrument Flying, 1 December 1976

Air Force Manual (AFM) 51-40, Air Navigation, Flying Training, 1 July 1973

Boeing 737 NG Flight Crew Training Manual, Revision 12, June 30, 2013

Dassault Falcon 900X Crew Operational Documentation for Dassault non EASy (CODDE), Original, March 26, 2010.

FAA-H-8083-15, Instrument Flying Handbook, U.S. Department of Transportation, Flight Standards Service, 2001.

FAA Orders 8400 and 8900

Gulfstream G450 Airplane Flight Manual, Revision 35, April 18, 2013

ICAO Doc 8168 - Aircraft Operations - Vol I - Flight Procedures, Procedures for Air Navigation Services, International Civil Aviation Organization, 5th edition, 2006

Revision: 20170915
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