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Origins of Knot and Nautical Mile

by Jeremy Cox 1. June 2006 00:00
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On June 26th it will be the sixtieth anniversary of the day that the United States Army Air Forces and the United States Navy officially adopted the ‘Knot' and ‘Nautical Mile' as the official measurement for Speed and Distance in the air. With this auspicious historical event in mind, have you, like me, ever wondered what the origins are of these perplexing measurement units?


According to a free online Encyclopedia, a Knot is a unit of speed… it is not a Standard International (SI) unit, and although discouraged, its use is accepted for use around the world for Marine and Aviation purposes… …Although knots do not fit within the SI system their retention for nautical and aviation use is important for navigational reasons because the length of a nautical mile is almost identical to a minute of latitude. I.e. if you slice Earth into two equal halves right through its centre along the equator for example, then divide the perimeter (its circumference) into three hundred and sixty degrees, then each degree into sixty arc minutes, the resultant length is approximately one nautical mile. Therefore one nautical mile is the arc distance of about one minute of a degree (or one sixtieth of a degree) of the Earth. As a result distance in nautical miles on a navigational chart can easily be measured by using dividers and the latitude indicators on the side of the chart.

It goes on to provide the following definition:… 1 knot = 1 nautical mile/hour = 1.852 km/h exactly. This is based on the internationally agreed length of the nautical mile… …Knot is sometimes mistakenly used to refer to the nautical mile itself, but this is incorrect…

Okay, so how did a ‘Knot' come into being?

This is where it really gets interesting.

Shortly after the invention of the sailing vessel, early sailors wanted to determine how fast their vessels were travelling as they sailed out of sight of the land. Ingeniously they achieved this by throwing a wooden log into the water and then observing how fast the vessel moved away from it. This method was named" 'Heaving the Log' and was not improved upon until the Sixteenth Century when the 'Chip Log' method came into being. This improved method of speed determination employed the use of a weighted wood panel tied to a reel of knotted rope. This rope had knots tied in it at approximately every fifty feet. When the Chip Log went over the side, the number of Knots that slipped through the hands of the sailor holding the rope, would be counted off during the time that it took for the grains of sand in an inverted ‘Hour-Glass', Sand-Timer to completely leave the time bulb that was calibrated to time the elapse of thirty seconds. This simple method provided a fairly accurate measurement of the number of nautical miles per hour that the vessel was traveling. For example, if ten knots went overboard in thirty seconds, then the ship was moving forward at the speed of ten knots or ten nautical miles per hour.

Another free encyclopedia site tackles the issue of how the approximation of the ‘Chip Log' Knot was tightened up, as follows: …We say approximate because if you choose to slice Earth along the line that goes through the North and South poles you would get a slightly different result due to the fact that Earth is not a perfect sphere - it is slightly flattened at the poles. The difference between the polar and equatorial diameter being about twenty three point four nautical miles out of six thousand, eight hundred and eighty nautical miles. The exact value for the nautical mile is taken to be the average of the two (i.e. polar and equatorial) which equals:

1 nautical mile = 1.15 miles = 1,852 meters = 6,067 feet

Since the majority of the world now uses the Metric System, interestingly enough, in the seventeenth century the Meter came into being and was defined as one part in ten million of the distance from the North Pole to the Equator along the meridian (an imaginary circle perpendicular to the horizon) that passes through the city of Paris.

Staying with the Knot, or Nautical Mile, later on in naval history, the hour-glass, sand timer was recalibrated to measure twenty eight seconds, and the knots were spaced out at exactly forty eight feet (which is equivalent to eight fathoms.) Under this arrangement a vessels speed was pretty much ‘spot-on'.

How about that!?!

As an aside, did you know that the term ‘Cockpit' comes from the Royal Navy of the Seventeenth Century? The cockpit was the area where the junior officers were stationed. Eventually this lead to the word being used to refer to the area towards the stern of a small decked vessel that houses the rudder controls.

Equally of interest, did you know that the name: ‘Pilot' comes from the Dutch word "pyl-lood". According to the encyclopedia at Wikipedia.org …The word pilot is supposed to have been derived from the word "pyl" and "lood". The word "pyl" stands in Dutch for everything vertical or straight as well as the height of the water. The word "lood" stands for "lead"; the dense metal used when making soundings. The combination of the two words describes "the person who is using the lead in a vertical way to obtain the water depths". In very ancient Dutch also the word "lodes-man" is sometimes used, having more or less the same implication.

As the great actor Michael Caine sometimes says: "Not a lot of people know that!"

So what other nautical terms do you know that have made it into the vocabulary of our aviation industry? Any input that you care to make will be of great interest to all of the readers here at Globalair.com. So please don't be bashful and go ahead and write your comments and suggestions here. Please don't forget that whatever you write here, can be seen publicly by everyone that visits this page, so please be funny, be inspired, but most importantly of all, please be nice. ‘Au revoir' until next Month.

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Jeremy Cox

NTSB Decision Makes Difference in SB's Compliance

by Greg Reigel 1. June 2006 00:00
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© 2006 All rights reserved.

In a recent article I wrote about compliance with mandatory service bulletins. The article raised, but did not answer, the question of whether a manufacturer's specification that its maintenance manual includes all service bulletins creates an obligation under the Federal Aviation Regulations ("FAR's") to comply with those service bulletins. A recent opinion by the National Transportation Safety Board ("NTSB") has answered that question in the affirmative and, in the process, has raised potentially serious implications for both aircraft owners and aircraft mechanics.

In Administrator v. Law, the FAA issued an order suspending the mechanic's airframe and powerplant certificate for 180 days for violations of FAR's 43.13(a) and 43.2(a)(1) and (2). The order followed an inspection performed by an FAA air safety inspector after one of the mechanic's customers notified the FAA that he believed the work the mechanic had completed on his aircraft's engine rendered the aircraft unairworthy.

According to the FAA, the mechanic sent the crankshaft, connecting rods, and pistons from a Textron Lycoming engine to a non-certified facility for balancing and then approved the engine for subsequent service. The FAA's complaint also alleged that Lycoming had no approved process for balancing crankshafts, connecting rods, or pistons in the field and that the mechanic ordered a non-certified employee to perform a magnetic particle inspection of the engine's crankshaft, and that the mechanic's employee did not follow the inspection requirements of a Lycoming Service Instruction bulletin. Finally, the FAA claimed that the mechanic performed a ground run-up of the engine that was not consistent with any approved standard or technical data acceptable to the Administrator.

The mechanic appealed the FAA's order to the NTSB. At the hearing, the FAA offered into evidence the service bulletin at issue, Textron Lycoming Service Instruction No. 1285B (May 23, 1997), which required that "[p]ersonnel performing Magnetic Particle Inspection shall be qualified and certified in accordance with ASNT Personnel Qualification SNT-TC-1A or MIL-STD-410." Although the mechanic did not dispute that his employee did not hold any certificates when he completed a magnetic particle inspection on the Lycoming engine in question, the mechanic argued that manufacturers' service instructions do not apply to mechanics performing maintenance on Part 91 aircraft. At the close of the hearing, Administrative Law Judge Geraghty held that the mechanic had violated each of the FAR's cited by the FAA. However, he reduced the suspension of the mechanic's A & P certificate from 180 to 120 days based upon the mechanic's apparent misunderstanding of the FAR's violated by the mechanic. The mechanic then appealed the ALJ's decision to the full NTSB board.

One of the mechanic's arguments on appeal was again that a mechanic is not required to comply with manufacturer's service bulletins, instructions, or letters in the absence of an Airworthiness Directive mandating such compliance. The Board disagreed and held that "[w]hile compliance with service instructions or service bulletins may not be mandatory in the absence of an Airworthiness Directive, a manufacturer may legitimately incorporate such service publications into a manual by reference." In this case, the Lycoming overhaul manual incorporated all future service instructions by reference: "In addition to this manual and subsequent revisions, additional overhaul and repair information is published in the form of service bulletins and service instructions. The information contained in these service bulletins and service instructions is an integral part of, and is to be used in conjunction with, the information contained in this overhaul manual." Based upon this language, the Board found that the mechanic's use of a non-certified person to perform the inspection and failure to use the manufacturer's prescribed inspection technique violated the FAR's as alleged by the FAA.

The Board's decision on this issue is interesting in that it does not cite to any precedent to support its position. Nor does a cursory search of NTSB opinions disclose any such precedent. Yet the Board has definitely sent a signal to manufacturers that they can require compliance with service bulletins that may previously have been ignored by aircraft owners/operators because they were not mandated by an airworthiness directive simply by incorporating the service bulletins by reference into their manuals. Keep in mind that not all manufacturers' manuals include this type of "incorporation by reference" language. However, many do. And it is likely that many more manufacturers will include this language in the future. As a result, a conservative analysis of this decision reveals potentially serious and far-reaching implications that will affect both aircraft mechanics and aircraft owners.

For aircraft owners, it will no longer be enough to perform a cost benefit analysis to compare the cost of compliance (How much will the labor or parts required by the service bulletin cost?) with the benefit obtained by complying with the service bulletin (Will compliance enhance the safety or value of the aircraft or limit the aircraft owner's liability exposure to third-parties?). If the manufacturer's manual includes the "incorporation by reference" language, compliance will be mandatory in order to have an airworthy aircraft. Unfortunately, this will likely raise the cost of maintaining an aircraft. However, failure to comply will expose the aircraft owner/operator to potential FAA enforcement action.

For aircraft mechanics, it will no longer be enough to simply expect the aircraft owner/operator to supply any pertinent service bulletins. The aircraft mechanic will need to be aware of applicable service bulletins and to communicate the information to the aircraft owner/operator. This may mean increased subscription costs to add service bulletin databases to the aircraft information maintained by an aircraft mechanic. If the aircraft owner/operator does not authorize the work, the aircraft mechanic will not be able to sign the aircraft off as airworthy or return the aircraft to service. Relying upon an aircraft owner/operator's representation that he or she has provided you with all applicable service bulletins or claiming that the aircraft owner/operator did not authorize compliance with a service bulletin will not be defenses for an aircraft mechanic's returning an aircraft to service in an unairworthy condition due to non-compliance.

As always, an aircraft owner/operator's decisions regarding maintenance are best made after discussion and consultation with a trusted aircraft mechanic. This NTSB opinion may well take some of the discretion out of the decision-making regarding whether or not to comply with a service bulletin. In the future, it will be in both the aircraft owner/operator's and aircraft mechanic's best interests to be informed regarding service bulletin applicability and compliance.

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Greg Reigel

Cost Saving Methods

by David Wyndham 1. June 2006 00:00
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Fuel costs are rising once again. Insurance costs never seem to fall. Even if business is good, those bills seem to be increasing faster than revenues. (If business is poor, that's fodder for a different article). How do you fly the same and not spend more?

One thing is to look at your current flying schedule. Can several trips be combined into one? Can the Monday trip to Des Moines be combined with the Tuesday trip to Cedar Rapids? If Kansas City is on the way to Omaha, maybe you can drop off someone? While technically this is flying less, you are still accomplishing the same mission. This will require the folks who use the aircraft to agree to some schedule adjustment. If the "big boss" dictates this, others will follow along.

Save in fuel costs. All operators have a choice in where they purchase fuel. While choosing an FBO based solely on fuel price (or any other single requirement) isn't necessarily the best, work with the FBO's you frequent most often to negotiate the best prices. When traveling to new destinations, make use of fuel surveys and handling agents to see where the savings are. Ask for a discount - if you don't ask you'll never get one. Go to https://www.globalair.com/airport/ and get up to date fuel prices for your destination airport. Call the FBO to confirm the price and other fees before leaving home.

In addition to negotiating with the FBO's directly, investigate fuel discount programs. It may be by using a fuel card or a professional association discount. These programs and discounts change, so it is best to review these on some sort of scheduled basis, at least annually.

Maintenance is one of your biggest cost areas and one where you do have the most control. Evaluate how you do your repairs and overhauls. Using loaner parts while yours are repaired may be less costly than exchanging for new. As you get your own part returned, you'll know the history of that part.

Maintenance tracking software is a valuable aid in determining where your maintenance expenses are and in managing your maintenance. You can't manage what you can't see. What about warranty? On a new aircraft, we all keep very careful track of what repairs are in warranty. But even older aircraft have many new parts installed. Those parts typically carry some sort of warranty. Tracking their ages/hours/cycles can result in savings should they need replacement and is something ready made for automation.

Guaranteed Maintenance Programs can be both a savings and an increased expense. They can be an effective way to manage your costs and avoid high expense years such as when the engine(s) are due for an overhaul. The also offer an insurance against unexpected expenses and may add value to the aircraft at resale. Still, the programs do have you pay now for future expected expenses. They warrant careful consideration, especially if acquiring a new aircraft.

Replace your aircraft with a newer one. OK, I know we are talking of saving money so how can getting a new aircraft save money? If the newer aircraft requires a lot less time in maintenance than your current one, then you (a) save in maintenance costs and (b) get increased utilization due to increased availability.

We've done numerous aircraft replacement studies and over time, newer aircraft tend to cost less to own and operate than older ones. There are always exceptions, but when you take into account how much time is lost by having your older aircraft in for maintenance, the numbers favor newer aircraft. This can be a tough sell, so you'd better have your reliability and availability data together, plus do your homework on costs before even bringing it up.

One last item is to make sure to communicate to management what you are doing and how to interpret your costs correctly. Paying out for a major phase inspection or an engine overhaul may make it look like your costs are too high. Educate the CFO as to the nature of aircraft costs. That $250,000 overhaul might have taken eight year's worth of flight hours to accrue. Don't assume they realize that. Let them know you are concerned about managing costs and keep them informed as to what you are doing to minimize costs while maintaining the highest levels of safety and service.

This is an interactive article and we would appreciate you adding any of your cost savings tips no matter how large or small, corporate operator or piston owner. Your suggestions on cost saving could possibly save enough for another owner/operator to keep their aircraft!

Work SMARTER, not harder. You already work hard!


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