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Route planning

Revision: May 08, 2012, at 05:22 PM

Module content

The four elements of navigation are

  • position
  • direction
  • distance
  • and time

And distance by time is ground speed.

There are four systems or techniques of air navigation

  • pilotage
  • dead reckoning
  • position fixing
  • and homing


Pilotage, dead reckoning and (with the introduction of GPS) homing are the primary navigational techniques for pilots of light recreational aircraft and, like many air navigation terms, they are centuries old nautical terms.

The first steps in flight planning entail

  • ascertaining general weather conditions
  • selection of a safe route
  • plotting it on a chart
  • checking the status of airfields along the route
  • and calculating preliminary fuel requirements.

This is somewhat iterative- you will first have an idea of your destination and route options, and will refine these based on weather, airfields and fuel requirements. But these plans may well change on the day or in flight due to weather or other considerations. It is always prudent to have a Plan B and Plan C up your sleeve should you need it.

3.1 The four navigation techniques

Pilotage (map following)

Pilotage is navigation by visual reference to landmarks – the art of visual track keeping – which thus requires that the ground is, more or less, continually in sight. In the early days all air navigation was by pilotage with some crude dead reckoning, indeed the first Pilots' Directions published by Elrey B. Jeppesen in the 1920s, for the early air mail pilots in the USA, were just notes about the landmarks along a route. As accurate aerial charts became available then aerial dead reckoning became much more refined.

Map reading is the essence of pilotage.
It entails

  • a continuous in-flight survey of the planned route (pre-plotted on the chart);
  • identification of the upcoming chart features on the ground, i.e. reading from map to ground in continuous contact;
  • and determining the actual location relative to the planned position.

Following the determination of that position (and thus the actual path over the ground) dead reckoning is then used to determine the "navigation solution", i.e.

  • the ground speed and the track error (the angular difference between the intended route and the actual path)
  • the subsequent course correction(s) necessary to regain and maintain the intended route
  • and a revised arrival time.

Only when uncertain of your position will it be necessary to note prominent ground features – and their relative positions – and then find such juxtaposition of features on the map, i.e. reading from ground to map. Map interpretation is an acquired skill; inability to relate the map to the ground features below is not an uncommon experience on the initial attempts. Some people find it very difficult to master. In more remote, and rather featureless, areas what seem to be the major features on the surface may not be discerned on the chart, and vice versa.

Dead reckoning

Dead reckoning [DR] is deriving the current position, or a future position, mathematically from a planned position or the last known position. DR for light aircraft is, or should be, essentially simple navigation by clock, compass and mental arithmetic. Most of the DR for RPT and military aircraft is done within the electronic circuitry of advanced navigation systems such as inertial navigation systems [INS] which calculate a new spatial position, from the previous position, about 100 times per second.

DR was born in the early days of oceanic sailing vessels: every hour or two during the voyage the log (a quadrant shaped piece of wood weighted to float upright with an attached log-line knotted at intervals) was dropped over the stern of a vessel under way and the vessel's speed was reckoned from the amount of line paid out over a particular period of time. In 1637 an English mathematician and navigator, Richard Norwood, calculated that the spacing between knots should be 47.25 feet with a 28 second sand glass being used as the timer. If you do the calculation, using the then estimated 6075 feet to the nautical mile, you will see that the number of knots that passed over the stern rail during the 28 second period equals the ship's speed in nautical miles per hour: hence knots. The log was presumed to be 'dead in the water' i.e not dragged by the ship or affected by tide or current. Each reading was marked on a log-slate and, during each watch, the course, speed and distance reckonings – adjusted for tide and current – were entered in the logbook.

Dead reckoning has a limitation in that errors in plotting, wind velocity estimation, course steering and timing etc are cumulative and the true position of the aircraft can't be verified unless it can be determined by pilotage [landmark reference] or some other position fixing technique.

Position fixing

Position fixing navigation techniques are usually radio based and encompasses simple techniques such as plotting the intersection of the bearings from two radio beacons through more complex systems such as VOR/DME to Loran, Decca, Omega and GPS which are both position fixing and homing. Such systems usually incorporate some degree of electronic dead reckoning.

The typical GPS unit uses continuous position fixing (GPS) plus electronic dead reckoning to calculate a new bearing, distance and time to the next waypoint.

The non-radio based position fixing techniques are celestial; star sights or sun sights.

Homing

Homing is radio based and encompasses non directional beacon [NDB] and VHF omnirange [VOR] homing through to Instrument Landing Systems [ILS] and Global Positioning System [GPS].

The pages of this navigation guide cover the essentials of pilotage and manual DR but a section on supplementary navigation techniques provides an introduction to NDB, VOR and GPS for VFR recreational pilots. In addition there is a module describing electronic planning and navigation systems for light aircraft.

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3.2 Fuel planning

Fuel related accidents or incidents are a common occurrence, caused by fuel exhaustion [all fuel on board consumed] or fuel starvation [pilot mishandling of the fuel system so that available fuel is blocked from delivery to the engine] — please ensure you are not this week's statistic.

Before undertaking a cross country flight the pilot must know the total usable fuel capacity and the rate of consumption at the planned cruising speed. The fuel consumption rates supplied by engine/aircraft manufacturers, unless contained in a formal pilot's operating handbook, must be viewed somewhat sceptically, they may be achievable with an 'as new' engine cruising at the best endurance power setting but not reflective of the consumption at a more useful cruise speed, say that at 75% power.

Fuel must be allowed for consumption at the departure airfield, for the climb and for circuit delays and landing at the destination. In addition the pilot is required to plan a fixed fuel reserve.The amount planned is a matter of personal discretion but should not be less than 30 minutes in good flying conditions but a greater amount if there is any doubt about the wind velocities or other conditions. This reserve should not be planned for use, i.e. wherever the aircraft is landed there ought to be at least 30 minutes fuel in the tanks.

It is vital to be able to measure fuel consumption during flight so a reasonably accurate fuel contents gauge, sight gauge or an inflight view of the fuel tank content is necessary. It is good practice to maintain a history log in the aircraft where the actual fuel consumption per flight hour is entered at the conclusion of each flight. Such a history log, showing fuel consumption history, provides valuable information both for future flight planning and for monitoring engine performance.

When planning a cross country flight the objectives are to arrive at the planned destination safely, with a reasonable reserve of fuel in hand and without affecting the safety of others whilst enroute; or even creating a possibility that safety might be affected. But remember the first rule of aviation – fly the aeroplane at all times, navigate when able and always be a few minutes ahead of the aeroplane. When navigating a light aircraft, and particularly an open cockpit ultralight, a person's capacity for mental arithmetic is not as good as it is when sitting at home. Nor is it easy, or maybe even possible, to manipulate navigational tools in flight and it is very difficult to handle charts, pencils and notepads in the cockpit: thus preflight preparation should be directed towards reducing and simplifying the inflight work load.

You should have a good acquaintance with the flight envelope of the aircraft, both with and without a passenger. In particular you must know the optimum cruise speeds obtained when cruising at say 75% power plus the proven fuel consumption, in litres per hour – at that throttle setting and aircraft weight.

Calculate the maximum sector time allowed as follows

CalculationExample
Total Usable Fuel64 litres
divided by Fuel Burn16 litres/hour
equals Fuel Endurance4 hours
less Reserve30 minutes
equals Maximum Advisable Sector Time3 hours 30 minutes

Never equate fuel consumption with distance- it is TIME you have in your tank.

Light aircraft consume 40% to 50% more fuel in a maximum power climb than at a normal cruise setting. It is normal practice to initially climb away at best rate of climb speed [Vy] until a safe height is reached, then airspeed is allowed to increase to a suitable enroute climb speed, while maintaining maximum allowed climb power, until the cruise altitude is reached. The extra fuel consumption during the climb can be estimated from the normal rate of climb achieved e.g. rate of enroute climb 250 feet/minute = four minutes per 1000 feet, then extra fuel consumed [~50%] is two minutes fuel per 1000 feet climbed. This extra fuel will be used whatever power setting is used in the climb, it is the chemical energy exchanged for the potential energy of height.

You should know these numbers for your aircraft from memory-
Flight planning

  • Fuel capacity- total usable fuel
  • Fuel burn- rate that it is burnt at cruise
  • Fuel endurance- total time in the tank

During flight

  • time remaining in your tank

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3.3 Airspace and Airfield check

Ultralights (or any aircraft) may not enter controlled airspace or land at airfields within controlled airspace without clearance from ATC- this may be prearranged by telephone for NORDO aircraft or via radio for radio equipped aircraft.

Aircraft may not land at airfields in a Mandatory Broadcast Zone MBZ unless radio equipped or flying in loose formation with a radio equipped aircraft. Radio calls must be made prior to entering the MBZ and at the designated intervals.

NORDO aircraft may land at any uncontrolled airfield, exercising due care and lookout. Some uncontrolled aerodromes have a locally operated facility, a Universal Communications facility [UNICOM] which provides information on local conditions. Where such a facility is operating it is vital for NORDO aircraft to maintain a careful lookout, as other radio equipped aircraft operating in the area may not be as vigilant as they should.

All civilian airfields can be classified as public or private. Public airfields are usually owned by the local government body and landing permission is generally not required although it is always wise to check. Private airfields usually cannot be used without prior permission from the owner, except in an emergency, even then there may be problems with trespass. Landing and parking charges apply at many airfields.

There is much to be considered when planning a landing at an unfamiliar airfield or, indeed, a familiar airfield. The current landing charts from the Visual Flight Guide (NZAIP Section 4) and NOTAMS should be fully consulted, particularly to check the circuit procedures and stated hazards.

For unlisted airfields, it is always wise to precheck with the owner/operator about the airfield conditions. (It is too late to find out the surface has been softened by rain when you are up to the axles and about to tip over.)

Hazards

You must be aware of your aircraft's landing (and subsequent take-off) performance in normal, soft field and short field conditions and you should perform a safety audit of the destination and alternate airfields for length, slope, surface condition, approach and go-around hazards, stock and wildlife hazards, tyre and wheel hazards, and any commonly occurring micro-meteorological hazards.

Check runway directions and expected wind conditions and be wary of airfields with single runways= crosswind conditions may be beyond your aircraft's capability. Be particularly wary of airfields with 'one-way' strips, they are extremely tricky, if not outright dangerous, for those not familiar with the atmospheric conditions which could exist.

The availability, and location, of suitable fuel should be checked.

Remember, just because your assessment concludes that you can safely land at a particular airfield it does not guarantee that you will be able to take-off safely.

Local knowledge

Local pilots are a valuable resource when planning flights into unfamiliar territory or airstrips. They know the best way to do things- the easiest routes, easily identifiable reference points, places to avoid, local procedures, and where that rabbit hole is on the field. And they can provide weather reports from a microlight pilot's point of view. Make use of them- they are generally happy to help.

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3.4 Route construction

The route you choose will depend a lot on the capabilities of you as a pilot and the facilities, equipment and performance of your aircraft.

  • If you have a low performance aircraft with limited endurance and no radio, you will tend to choose a route that sticks to class G airspace and uses VFR transit lanes around controlled airspace. Your route will be a series of shorter legs (limited by endurance) with fuel availability at each waypoint being important. If there is any wind, you will need to consider the terrain and chose a route that minimises the adverse effects of wind (headwinds, turbulence). You would also choose a route with plenty of options of alternate airfields or land-out options.
  • If you have a higher performance aircraft with good endurance and radio and transponder equipped, your route options will be less restricted. Longer legs, using controlled airspace when required, with less consideration of wind.

But in both cases the weather- particularly incoming fronts, cloudbase and wind- are an important factor in your final choice of route, and may force a change of plans enroute- be prepared.

Having decided a destination the first step is a rough calculation to ascertain

  • the track – the path over the ground;
  • the 'distance to run' from your departure point;
  • the approximate sector time
  • and the viability of the proposed flight.

The charts needed are a current VNCs.

Route construction is often done the day before planned departure, or even earlier if an extensive cross country flight is planned.

With a soft pencil and a rule draw a preliminary line on the VNC between your departure and destination – you may have to overlap charts– and then check along the line for areas to be avoided – 'tiger country' i.e. rough or heavily forested or hilly areas where there is a limited availability of open, cleared, flat land for an emergency landing. If possible avoid long stretches of featureless terrain and also terrain exceeding 3500 feet elevation.

Note any other airfields near the line.

Now decide which areas of terrain to avoid and find a suitable diversion around them. If that diversion takes you quite a distance from the direct line then so be it; it won't make that much difference to the total distance flown. If there are areas of scenic, or other, interest evident on the chart you might plan to overfly them even if it does makes a zigzag path.

Tracking around and beneath controlled airspace

Note all controlled airspace (boundaries and lower levels, transit lanes, danger and restricted areas, MBZs, MOAs and SPZs). You may elect to enter rather than go around/under controlled airspace, but ensure that you have the necessary equipment (VHF radio, possibly transponder) or prior clearance.

When planning to track near a CTR be aware that you must avoid incursion into controlled airspace without clearance from ATC. A VHF radio is advisable when planning to operate close to a CTR- if you do get caught between rising terrain and a lowering cloud base you can always call Air Traffic Control and request clearance to track through the edge of the CTR because of deteriorating weather. ATC are always very helpful but unauthorised entry into the CTA or CTR ( the dreaded 'violation of controlled airspace' or VCA) is a safety hazard and may earn a substantial fine.

Waypoint selection

You need to find suitable, i.e. readily recognisable, point locations or waypoints for monitoring flight progress and/or to mark the points of diversion and consequent turning points.

Suitable waypoints are

  • airfields
  • major road junctions
  • small towns
  • intersecting line features (road, rail, transmission lines)
  • water features (lakes, rivers, coasts)
  • distinctive hills, ridges, peaks
  • microwave and radio towers

You may also see some highly visible linear features – roads, railways, transmission lines, rivers, beaches – that roughly parallel your intended track for a reasonable distance. Plan a track divergence to intercept and then follow such line features – and be aware that the 'Rules of the Road' require aircraft to track to the right of a line feature or when flying within a valley or any air traffic lane.

Mark all the turning points on the chart, joining them to form the route segments of the required track. These turning points will also be used as fuel consumption checkpoints. Generally speaking a route that provides the best visual fixes and reasonably short segments is the best option.

Measure the total track distance using the scale (in nautical miles) printed on the map or alternatively use the latitude graticule printed along the meridians, each mark is one minute of latitude or one nautical mile. The printed scale is easier to read and thus less prone to errors. You can buy a ruler scaled in nautical miles for use with VNCs and you might buy a protractor at the same time.

Divide the total track distance by the cruise speed to get an approximate total time required. If the total time required is greater than the known maximum sector time then the flight must be broken into two or more sectors, by introducing refuelling stops at appropriate distances. This probably necessitates replanning the waypoints so that one or more coincide with an airfield with assured and suitable fuel supplies. Replot the route if necessary.

If the total time required is less than the maximum sector time then the first cut plan for the route to be followed may be viable but we have not yet taken into account the effects of wind, which may be considerable and are covered in the next module.

Forecast weather and winds should be ascertained as close to the planned departure time as possible but it is advisable to obtain a preliminary weather forecast the evening before the flight. If a very long flight is planned it is advisable to watch the weather patterns for a few days prior to the trip. Any Notams applicable to the area in which you intend to operate should also be obtained at that time.

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3.5 Plotting the route on a chart

Shown above is the route we plan to fly from an airstrip on a rural property – Koputaroa– to an airfield at Feilding (Taonui). The direct track is shown as a solid red line, with a track distance of 23NM measured against the tick-marks on vertical lines of longitude.

Looking at the terrain, the track presents no problem- the surrounding terrain is flat, Feilding is the highest point at 214 ft elevation! The high country to the east (2800ft) is well clear of our track. Provided there is not a strong easterly wind (unusual), there should be be no turbulence form the hills. We should be wary of strong westerly winds (common), as we are close to the coast- but provided we maintain a reasonable height AGL we should remain above any low level turbulence. A westerly wind may have a significant affect on our drift, so our heading may have to be somewhat west of the desired track.

But we have a problem with airspace! This is a complicated piece of airspace, so it is important to study it carefully.

  • Koputaroa is within the Manawatu CFZ which is from the surface to the lower level of class C airspace, frequency 122.6. The border is shown by a chain of diamonds, the details in a blue box just west of the Koputaroa airfield. We are OK to fly in this CFZ, we just need to maintain a watch on that frequency.
  • Koputaroa is beneath class C transponder mandatory airspace with a lower level of 3500ft. The border is marked by the purple lines, with details in purple to the east of Shannon. We need to keep below 3500ft.
  • There is a low flying area L366 just north of the field- we should climb to at least 500ft before transitting this area.
  • The lower level of the class C TM airspace drops to 1500ft just south of Opiki. We need to keep below it.
  • And around Karere we hit the Palmerston North Control Zone from the surface to 1500ft, transponder mandatory, frequency 120.6. We don't want to go through a busy control zone, so we will have to alter our track.
  • Closer to Feilding airfield, we clear the Palmerston North CTR, and are back under class C TM airspace with a lower level of 1500ft.
  • Fielding is also within the Feilding CFZ, surface to 1500ft, frequency 124.1. There is also a special message 6 advising transitting traffic to avoid the Feilding active circuit- but that doesn't apply to us.
  • The western end of the Palmerston North CTR has the Orua VFR Transit Lane T354, surface to 1000ft during daylight hours, frequency 124.1, with special message 17- transponder in mode A and C if fitted, and nav/landing lights on if fitted. T354 also shows arrows indicating to track on the right side if the transit lane to avoid opposing traffic.
  • There are also quite a few red aircraft symbols dotted around the area, indicating high density of VFR traffic. We need to maintain a good visual lookout.



The chart above shows our amended track to avoid controlled airspace and make use of T354 VFR Transit Lane. The short flight is effectively broken into 3 segments as follows...

Note that flying over flat terrain such as this at low level (100ft) with few spot features can be very disorienting! For this flight a useful plan in case you get lost would be to

  • track due north from Koputaroa until you see the transmission lines
  • follow the transmission lines until you intercept the river boundary for T354
  • track up the river (on your right) to Feilding township
  • follow the railway line to Feilding airfield

Checking minimum safe altitude

We now have to decide the minimum altitude at which each segment can be safely flown. In this example the decision is quite easy- the terrain is flat, less than 100ft AMSL, the only obstructions along the track are the transmission lines, the nearest hills are well east of track, and we have a ceiling of 1000ft in the Oroua transit lane. Given minimum altitude is 500ft AGL, flying at 800 AMSL will give us clearance above and below.

If this was more hilly/mountainous terrain, minimum safe altitude should take into account any ridges that need to be crossed, any significant peaks adjacent to track, and any obstructions (cables, aerials, transmission lines) that may be difficult to see in marginal conditions. 500ft clearance is the minimum you should plan for unless the visibility and conditions are very good.

The preliminary flight plan

We have now accumulated the non-variable part of our flight plan (ie assuming nil wind). We can calculate leg times and fuel burn to come up with a preliminary flight plan. Assuming 50kts and 15 l/hr out plan would look like this:

Before we can proceed further we must:

  • Ascertain the weather and the wind that are forecast for the period of our planned flight.
  • Check for Notams which may affect us.
  • Determine the time for Evening Civil Twilight (ECT) if our flight is planned for late in the day.

3.6 Obtaining weather forecasts, Notams, ECT

Weather forecasts

The official source of aviation weather forecasts is MetFlight-GA. This is a user pays service, requiring you to log in with a user id and password. These are issued to you by RAANZ when you first enter the system. Details of how to access weather from MetFlight-GA and interpret the information are detailed in the Meteorology section of the Training Manual.

NOTAMs

The official source of NOTAMs is the Airways IFIS website. This is a free service, but you need to log on with a user id and password to access the information. Once logged in select Area Pre-flight Briefing to get to this page-

Click on the areas for which you require a briefing, check NOTAM and ATIS (if you want the current terminal weather) and click on SUBMIT- your briefing will appear in a few seconds.

You can also select the Specific Pre-Flight Briefing option for a briefing tailored to onl;y those airfields and ares you will be flying to.

Note that these pages also have a link to MetFlight-GA. This is a quick way to get your NOTAMs and weather briefings in one hit.

You should always check NOTAMs before a cross-country flight. There are often cases where a pilot fies into familiar territory and airfields without checking NOTAMs, only to be caught out with an unexpected runway closure or event that he should have been aware of.

ECT

Twilight tables are also available off the Airways IFIS website. Select 'Planning info/Twilight Tables and then which table option you require- the Interactive option is good.

Note that the values for MCT and ECT are in UTC format- you need to add 12 hours (or 13 when in NZDT) to get local time.

The next module deals with the effect of wind on our flight plan.