Cross Country Planning and Flying
Part One

There is much more to making a cross country flight than simply "gas and go". This article presents many of the things you should consider in planning a route from fuel availability and accommodations, to making educated judgments as to what conditions you may expect on the flight.

A rule of thumb for estimating the effect that altitude has on your aircrafts performance is also given. This can be very important if your flight will have you operating at high altitudes.

1. Flying Cross Country in a Challenger is an Adventure:

The FAA considers a flight that exceeds 25 miles from the point of origin to be a "cross country". However, for the purposes of this article, I'm talking about flights exceeding one landing for refueling and continuing on to one or more destinations other than the point of origin.

Our planes and we are subject to the elements on a "cross country" flight and dependent on things that are made more important by the relatively low speed and short cruising range of our planes. Things such as the lack of storage space aboard the Challenger, fuel availability, repair facilities, possible ground transportation, food, toilet facilities, and a place to spend the night or to sit out bad weather along the way may present problems. All these must be addressed in planning a flight.

If flying from one friend's airfield to that of another friend, it may be as easy as calling and making the request for arrangements. If an airport has ultralight type aircraft operating on the field, be creative in trying to contact one of the ultralight owners to get the lowdown on any local help to be had with your planning. This can really be a great way of meeting some very fine folks.

Keep in mind that these flights are an adventure and not really a viable means of traveling long distances. But with proper planning and preparations you will enjoy the adventure and all the fabulous sights it will present!

2. Things to consider:

Familiarize yourself with the departure, enroute points, and destination airfields.

Record names of the airfields, their identifiers, communications frequencies and services available.

Note the layout of the runways and taxiways at each field. Pay attention to the orientation, length, elevation, and any obstacles on the approach to or departure from the field.

Gather the following data:

    Your fuel on board or capacity ______ Gals.
    Your average block/block fuel burn rate ______ GPH
    Your normal block/block cruise speed _______ MPH

Figure the approximate length of time you can stay aloft with 80% of the fuel on board.

    Stay time = .8 x fuel on board / Fuel burn rate = ______ Hrs.

Figure the approximate distance you can cover at your cruise speed and stay time.

    Distance = cruise speed x stay time = _______Miles

    (This must be considered the MAXIMUM leg length for preliminary planning as the wind direction and speed may adversely affect your ground speed)

Make a list of all personal belongings and equipment you will be taking on the flight with each item's weight and where it will be stowed in the airplane (arm) .

3. Map work

    1. Locate departure and destination airfields
    2. Locate possible alternate landing sites
    3. Familiarize yourself with enroute terrain features such as:

        Towns         Roads         Railroad tracks         Waterways
        Valleys         Mountain peaks         Mountain passes         Airfields
        Forested and open spaces         Restricted and Prohibited airspaces

Plan your route to take full advantage of the safety afforded by:

        Major roads         Railroad tracks         Towns
        Airfields         Valleys         Mountain passes

4. Insights relating to Flying the Weather

Changes in Terrain Elevation

Generally when flying from an area of lower elevation that is experiencing marginal weather to a higher area, conditions tend to worsen as the land elevation rises. The reverse is true going from higher to lower elevations.

Here are four things, nice to know, that can give a pilot a heads up on what to expect up ahead on his planned flight path:

    1. The temperature lapse rate of the standard atmosphere is approximately three degrees per 1,000 ft of elevation. This means that if the temperature at take-off is 59 F and your planned flight will have you climbing 6,000 ft higher, the temperature should drop by approximately 18 degrees to 41 F:

      • 3 x 6 = 18         59 - 18 = 41

    2. The pressure lapse rate of the standard atmosphere is approximately 1/2 psi per 1,000 ft. in the chunk of atmosphere we fly in. This means that on the above flight the atmospheric pressure can be expected to drop by 3 psi (6 x .5 = 3). There is approximately an 8 psi drop in pressure from sea level through about 16,000 ft.

    3. Assuming a sea level rate of climb of 750 ft/min and a take-off run of 300 ft, the calculation of multiplying factors for the rate of climb and takeoff run at that altitude would look something like this:

    4. Rate of Climb

        Pressure drop = 6 x 0.5 = 3 psi (altitude increase of 6,000 ft)

        1.0 - (Pressure Drop / 8) = 1 - (3 / 8) = 1 - 0.375 = 0.625

        0.625 x 750 ft/min = 469 ft/min (15% of this must be subtracted)

        15% of 469 = 70 ft/min

        Rate of climb at 6,000 ft = 469 -- 70 = 399 ft/min

      Takeoff Run

        1.0 - (Pressure Drop / 8) = 1.0 - ( 3 / 8 ) = 0.625 (as above)

        1.0 / 0.625 = 1.6

        1.6 x 300 = 480 ft (15% of this must be added)

        15% of 480 ft = 72 ft

        Takeoff Run at 6,000 ft = 480 + 72 = 552 ft

    5. True air speed (TAS) increases, over that of your indicated air speed (IAS), by 2% per 1,000 feet of density altitude.

The first three above rules of thumb, your actual performance numbers may vary by + or - 20% from those calculated by this method. Also if the temperature is higher than the lapse rate would suggest, the performance will be further degraded.

It should be noted that take-offs from other than hard surfaces will also increase the takeoff distance required. Numbers so calculated should only be used in the absence of the appropriate actual performance numbers, charts, tables or graphs.

Density Altitude Effects

When flying a long cross country requiring many hours, remember as the day goes by, the density altitude will almost always go up. This is especially true during the summer or when going from an area of lower land elevation to a higher one. Be sure you know and understand what this means to the airplane (hint, less performance all-round).

When flying in mountainous areas it would serve you well to check your density altitude as your airplane may be trying to operate at a much higher altitude than the altimeter is indicating.

It is easier to get yourself into this position than you may think. Then you will have a job on your hands just to maintain a decent cruising speed.

Another thing to remember about changing altitude is that the airplane will always fly by the indicated airspeed. That is, if the airplane stalls at 35 mph indicated at sea level, it will stall at 35 mph indicated at 10,000 ft.

If it climbs best at 50 mph at sea level, it will, within a mile or three, climb best at 50 mph at 10,000 ft. The point here is this: Do not confuse yourself with a lot of performance numbers for different altitudes and density altitudes, use the speeds you usually use.

It is true that the speeds do actually change, but by so little as to be meaningless for all practical purposes unless you are a very accomplished pilot. Remember also that the airplane will take longer to reach take-off speed at higher altitudes and will appear to be moving faster relative to the ground than you would expect.

FLY THE AIRSPEED, not your visual clues!

Relating to winds and movements of an air mass, the "gradient level" is by definition 2,000 ft above the ground where it is no longer subject to local terrain features such as man-made objects, hills, trees, rivers, and so forth.

If the wind direction and speed at the gradient level is blowing from lower toward higher elevations, you can expect a lifting of the air mass making it easier to climb over ridges and mountains whenever you are flying with the wind.

If unsure of the wind direction and speed, never approach a mountain ridgeline at 90 degrees. The wind may be in your face and spilling over the ridge like a waterfall. This air may be falling at a rate greater than your plane's ability to climb, especially at high altitude or at a high density altitude. It's best to approach at 45 degrees as this gives you the most recovery options, one of which is as easy as simply turning away from the ridgeline.

Everyone knows to avoid thunderheads. One thing to remember about them though is the anvil at the top will be pointing in the direction that the storm cell and the wind are moving. Any hail formed in the cell will at times fall down wind of the cell, that is on the side the anvil is pointing, from what may appear to be "clear skies".

Also beware of clouds that look like these:

They like to form over mountain ridges and appear to be of little consequence but in fact, they are very dangerous and are to be avoided. These clouds are called lenticular clouds and are formed by much the same forces that create those vapor clouds around fast flying aircraft. That is fast moving, turbulent air. If you see these clouds in your flight path give them a wide berth.

A few observations about the wind:

If you put the wind to your back, there will usually be a low pressure area to your left. It may be 1,000 miles out there but it is usually there. Likewise a high pressure area may be somewhere to your right.

"Why is this good to know?" you may ask. Well for one thing, it will help you understand the bigger weather picture. For instance, air (wind) moves from high pressure toward low pressure, and in the northern hemisphere counter clock wise (CCW) around the low and clock wise (CW) about the high. In the southern hemisphere the flow directions around a high or low are reversed.

As far as wind is concerned, a high is like a mountain and a low like a valley. The wind direction for the most part will be about 15 degrees across the "contour lines" of equal pressure, outward on the high and inward on the low.

Just think of all that can be discerned from these simple observations.

In your minds eye, picture these lows and highs along with their normal flow patterns. Now place yourself on the map facing generally in the direction you will be flying.

Then, using the "wind to your back" rule, place the low pressure area to your left and the high to your right. Remember also that the closer together these areas are and the deeper the low and the higher the high, the stronger the wind will be.

The wind will bring along with it many of the elements, such as moisture content, cloud cover and such, that were present in the area from which it came. Remember also that you will be moving through these air masses, not just along with them. Pretty neat info for only starting with "The Wind to your Back".

Now I don't mean this to replace a good weather briefing, but in cases where one is not available it will prove to be far better than nothing. So remember the phrase "THE WIND TO YOUR BACK" and all that this can tell you about what you might expect on your flight.

In part two, the actual planning and a couple of "how to" flight aid tips.

Author:   Ralph Shultz