basic aircraft navigation

introduction

Navigation is the art and science of getting from point "A" to point "B" in the least possible time without losing your way. In the early days of aviation, navigation was mostly an art. The simplest instruments of flight had not been invented, so pilots flew "by the seat of their pants". Today, navigation is a science with sophisticated equipment being standard on most aircraft.

The type of navigation used by pilots depends on many factors. The navigation method used depends on where the pilot is going, how long the flight will take, when the flight is to take off, the type of aircraft being flown, the on-board navigation equipment, the ratings and currency of the pilot and especially the expected weather.

To navigate a pilot needs to know the following:

Starting point (point of departure)

Ending point (final destination)

Direction of travel

Distance to travel

Aircraft speed

Aircraft fuel capacity

Aircraft weight & balance information

With this information flight planning can commence and the proper method of navigation can be put to use.

Basic Navigation

Pilotage

For a non-instrument rated, private pilot planning to fly VFR (Visual Flight Rules) in a small, single engine airplane around the local area on a clear day, the navigation is simple. The navigation process for such a local trip would be pilotage. (Bear in mind, however that the flight planning and preflight for such a trip should be as thorough as if the pilot is preparing to fly cross-country.)

The pilotage method of navigation developed naturally through time as aircraft evolved with the ability to travel increasingly longer distances. Flying at low altitudes, pilots used rivers, railroad tracks and other visual references to guide them from place to place. This method called pilotage is still in use today. Pilotage is mainly used by pilots of small, low speed aircraft who compare symbols on aeronautical charts with surface features on the ground in order to navigate. This method has some obvious disadvantages. Poor visibility caused by inclement weather can prevent a pilot from seeing the needed landmarks and cause the pilot to become disoriented and navigate off course. A lack of landmarks when flying over the more remote areas can also cause a pilot to get lost.

Using pilotage for navigation can be as easy as following an interstate highway. It would be difficult to get lost flying VFR from Oklahoma City to Albuquerque on a clear day because all a pilot need do is follow Interstate 40 west. Flying from Washington, DC to Florida years ago was accomplished by flying the "great iron compass" also called the railroad tracks.

Dead Reckoning

"Dead" Reckoning (or "Ded" for Deductive Reckoning) is another basic navigational method used by low speed, small airplane pilots. It is based on mathematical calculations to plot a course using the elements of a course line, airspeed, course, heading and elapsed time. During this process pilots make use of a flight computer. Manual or electronic flight computers are used to calculate time-speed-distance measurements, fuel consumption, density altitude and many other en route data necessary for navigation.

The estimated time en route (ETE) can be calculated using the flight distance, the airspeed and direction to be flown. If the route is flown at the airspeed planned, when the planned flight time is up, the destination should be visible from the cockpit. Navigating using known measured and recorded times, distances, directions and speeds makes it possible for positions or "fixes" to be calculated or solved graphically. A "fix" is a position in the sky reached by an aircraft following a specific route. Pilots flying the exact same route regularly can compute the flight time needed to fly from one fix to the next. If the pilot reaches that fix at the calculated time, then the pilot knows the aircraft is on course. The positions or "fixes" are based on the latest known or calculated positions. Direction is measured by a compass or gyro-compass. Time is measured on-board by the best means possible. And speed is either calculated or measured using on-board equipment.

Navigating now by dead reckoning would be used only as a last resort, or to check whether another means of navigation is functioning properly. There are navigation problems associated with dead reckoning. For example, errors build upon errors. So if wind velocity and direction are unknown or incorrectly known, then the aircraft will slowly be blown off course. This means that the next fix is only as good as the last fix.