"Pilotage" vs. "Dead Reckoning"

[jrenwick]

From the topic, "New 170a Owner":

. Hey, this pilotage stuff really works! ...

If you were completely out of sight of land(marks).... wouldn't that be called "dead reckoning" rather than "pilotage"?

back!

No.

Now listen up, all you folks who want to use the term "dead reckoning": According to American Practical Navigator, 1984 edition (because I haven't really kept up to date), page 59:

Dead reckoning is the determination of position by advancing a known position for courses and distances. A position so determined is called a dead reckoning position. It is generally accepted that the course steered and the speed through the water should be used, but the expression is also used to refer to the determination of position by use of the course and speed expected to be made good over the ground, thus making an estimated allowance for disturbing elements such as current and wind. A position so determined is better called an estimated position. The expression "dead reckoning" probably originated from use of the Dutchman's log, a buoyant object thrown overboard to determine the speed of the vessel relative to the object, which was assumed to be dead in the water. Appparently, the expression deduced reckoning was used when allowance was made for current and wind. It was often shortened to ded reckoning and the similarity of this expression to dead reckoning was undoubtedly the source of the confusion that is still associated with these expressions.

Now, this is from ocean navigation. When I first learned to fly, our navigation technique was called pilotage (never dead reckoning), because there is an important difference. At sea (i.e. out of sight of land), before there were any electronic aids like LORAN or GPS, the only way you could get a fix on your position was by celestial observations, which could only be done during twilight with sufficiently clear skies to catch a good glimpse of a star or three, perhaps augmented by the sun or moon. In between those times, the navigator would estimate a ship's position by advancing the most recent fix on the chart, based on the ship's heading and speed, corrected for drifts due to wind and current.

This is not what we do in our itty-bitty airplanes that don't cross oceans. What we do is pilotage, which is to calculate a heading to fly that we think will get us from A to B, and calculate the time it will take to do that, based on forecast winds aloft. Along the way, we get fixes as they become available by reference to objects on the ground, and use those to correct our pilotage. When eventually we arrive at where we expected to be, that's a fix. And a big sigh of relief, if Lihue was what you were aiming for.

If I had estimated my position at any point during the passage, that would have been dead reckoning. But we don't do that on short flights -- we wait for a fix, then correct the heading we think will get us to the destination. That's pilotage. It's a subtle distinction, really two sides of the same coin. But it's an important difference -- at least to navigation nerds like me!

Speaking of coins, sometimes you put in a nickel and get a lot back -- right George?

[Bruce Fenstermacher]

I agree with you John. To me in simple terms pilotage is all the techniques used whether they are using stars, sighting fixes, using electronic means or just plain old gut feelings plus any corrections calculated to get from one place to another. Pilotage also includes understanding weather and perhaps local weather patterns to anticipate the best course to take including not going at all.

Dead reckoning is a pilotage tool. I most often would use both terms together though most times including the term dead reckoning is not telling the whole story. I consider dead reckoning those times when I'm traveling a course, no matter what vehicle I'm in, that I am primarily using time, distance and heading to navigate from one place to another. This might be from one fix to another if there are no other means to find the fix or it might be from start to final destination while I'm in my airplane. It would also be when I've traveling in my car down an unknown road using my odometer and heading traveled to determine I've gone to far or need to turn at the next intersection.

I know one thing for sure. While I'm flying today I'm sure glad I'm practicing pilotage and GPS rather than pilotage and dead reckoning.

[GAHorn]

We are discussing AIR NAVIGATION and therefore should use the terms appropriate to that activity.

From the Airman's Information Manual (and also from William Kershner's excellent Student Pilot's Manual):

Pilotage: Navigation by visual reference to landmarks.

Dead Reckoning: navigation without the use of landmarks, usually by (determination of) wind-vectors, True Airspeed, heading, groundspeed, and estimated time of arrival at the destination.

Celestial navigation: Navigation by using a sextant to measure angles to heavently bodies to determine position.

(For those insistent upon using the methods prescribed for boating or naval operations, I believe that "Chapman's Piloting" is an established reference, and on page 444 of th 57th edition it states: "..a technique of navigation known as DEAD RECKONING , usually abbreviated to DR. This is the advancement of the boat's position on the chart from its last accurately determined location, using the courses steered and the speeds through the water. No allowance is made for the effects of wind, waves, current, or steering errors."
On the subsequent page: "Dead reckoning is the basic method of navigation to which you will apply corrections and adjustments from other sources of information."
Chapman's does not expressly use the term "pilotage" but instead uses the term "piloting" and defines it on page 32: "Piloting, which is navigation using visible references,..." )

Therefore, I submit that "DEAD RECKONING" is navigation using time and speed to compute distance travelled and heading to project desired course, without the use of landmarks.
"PILOTAGE" is navigation by the use of visual landmarks.
For the period of time in which the aircraft is navigated out-of-sight-of-landmarks over unmarked WATER (no buoys or other objects) using a compass and time.... the primary method of navigation would be DEAD RECKONING.
Subsequent to the sighting of a landmark such as a lighthouse, and between that determined position and the next visually confirmed position, the method would have been defined as PILOTAGE. IMO

(I will also submit that use of any radio receiver, whether VOR, TACAN, satellite, or inertial navigation system is "electronic-means" navigation.)

[jrenwick]

OK, George, I think you're right. We don't plot positions on a chart by dead reckoning, as would be done at sea, but just the act of estimating the remaining time to reach shore is, in essence, estimating present position by dead reckoning -- the calculations all having been done prior to takeoff.

[GAHorn]

Yes, Lindbergh used both methods in his New York to Paris flight. From Long Island Roosevelt Field (now a shopping center parking lot) to St. Johns, Newfoundland he used pilotage as he confirmed his positions by visual references to landmarks. This was important to him in order to confirm his groundspeed and accuracy of heading predictions.
After leaving the coast at Newfoundland, he utilized dead-reckoning for almost 19 hours until sighting the southern coast of Ireland and the English channel. (He briefly circled a fishing boat and attempted to communicate with them in order to determine the direction to Ireland. This was probably an action he took prompted by both fatigue and relief to see another object of recognition. But the boat did not constitute a "landmark" or other known position as he was unable to make his question understandable to the fishermen and also unable to elicit an understandable response from them. I suspect he was desperate to update his known position and for all he knew he was shouting over the noise of engine and wind at non-English-speaking people.)
After sighting land he continued on his flight-planned path and again used pilotage (including the sighting of a bonfire built upon an adjacent hill by Parisioners) to locate Le Bourget at night. His "great circle" path was actually a series of 500 mile long straight lines which, at the end of each, he made a small compass-course correction to the right, and flew another 500 mile straight line. At the time very few lights would be visible at night, and his feat was truly remarkable not only for his navigational skills but also for his endurance. (I don't know how many of us arm-chair-aviators would really be willing to risk such a flight in our single-engined airplanes. Jamie told me she'd take Air France and wait for me at the Louvre.)
This is an actual chart he used to plan his flight which he donated to the Geographical Society ten years later.



From the Charles Lindbergh society website, quoting from the Ryan technical specifications report to NACA, Lindbergh planned the entirety of his flight to be dead reckoning.
"During four weeks practically all his waking hours were occupied by this study of navigation and the preparation of charts and data for use in a dead reckoning flight. It should be borne in mind that he had practically no technical knowlege of the art of navigation prior to this time with the exception of such aerial navigation as he had had in his Army and Air Mail experience."
In other words, Lindbergh was very concerned that his lack of navigation experience would present a problem to his Atlantic crossing. He had absolutely no experience in long distance or great circle navigation and He planned entirely to rely upon dead reckoning for the vast majority of his flight.

Here is a copy of that document:

spirit.pdf